Opposite regulation of XIAP and Smac/DIABLO in the rat endometrium in response to 17β-estradiol at estrus
© Leblanc et al; licensee BioMed Central Ltd. 2003
Received: 28 July 2003
Accepted: 27 August 2003
Published: 27 August 2003
During rat estrous cycle, the endometrium proliferates in response to sex steroids and specific endometrial epithelial cells undergo apoptosis in absence of embryonic factors. The central executioner of apoptosis is a family of aspartic acid-specific cysteine proteases known as caspases. Smac/DIABLO is released from the mitochondria during apoptosis and its stimulation promotes caspases activation by neutralizing members of the inhibitor of apoptosis proteins (IAPs) family, such as X-linked inhibitor of apoptosis protein (XIAP). The aim of this study was to investigate the involvement of Smac/DIABLO and XIAP in the control of caspases activation in endometrium of cycling rats. Polyoestrus female rats were sacrificed at each stage of estrous cycle (diestrus, proestrus, estrus, and metestrus). Endometrial protein extracts were collected to perform Western Blot analysis. Alternatively, uterine horns were sectioned for immunohistochemistry (IHC). We and others showed previously the presence of apoptosis at estrus in rat uterine epithelium. In the present study, cleaved caspase-3, -6, and -7 fragments were detected at estrus. IHC confirmed that caspase-3 was present only in luminal and glandular epithelium at estrus. XIAP was highly expressed at estrus in both epithelial and stromal cells. In contrast, expression of Smac/DIABLO was elevated at diestrus, proestrus and metestrus but was minimal at estrus. Treatment of ovariectomized rats with 17β-estradiol induced XIAP expression and inhibited Smac/DIABLO protein expression in the endometrium. Cleaved caspase-3, -6, and -7 fragments increased in endometrial protein extracts following 17β-estradiol treatment. Expression of NF-κB and IκB proteins, and IκB phosphorylation status were detected in the endometrium but were not influenced by the estrous cycle. These findings suggest that Smac/DIABLO and XIAP are regulated differently and may play important roles in the regulation of endometrial cell fate. Moreover, this study confirms a key role for executioner caspases in the control of apoptotic processes at estrus in the rat uterus.
In the absence of embryonic factors during pre-implantation period in uterine luminal epithelium, glands and stroma cell death is found in a cycling fashion through the estrous cycle by a mechanism known as apoptosis. Estrogens and progesterone are directly responsible for the histological and morphogical changes in the uterus during estrous cycle. Studies have shown that apoptosis was induced in luminal epithelium at estrus in mouse  and rat [2, 3]. Other studies have shown that estrogen induces uterine epithelial cell proliferation and estrogen withdrawal results in cell death [4–6]. However, little is known about the cellular and molecular mechanisms involved in the regulation of apoptosis in the uterus. Our group has recently demonstrated that Akt, a serine/threonine protein kinase also known as PKB, is an important kinase involved in the control of endometrial cell proliferation and its expression and phosphorylation/activation are regulated during the estrous cycle, particularly through the action of 17β-estradiol . We have further showed a decrease in Akt activity at estrus which was accompanied by an increase in apoptosis in luminal epithelial cells. Whether downstream Akt targets might be involved in the regulation of proliferation/cell death in the endometrium is unknown.
X-linked inhibitor of apoptosis protein (XIAP) is a well known inhibitor of caspase-3, -7 and -9 [8, 9]. XIAP belongs to a family of IAP genes which represent critical regulatory factors of apoptosis signaling and regulation. The IAP family also includes c-IAP1 (HIAP2), c-IAP2 (HIAP1), NAIP and Survivin . Recently, we demonstrated in rat granulosa cells and human ovarian surface epithelial cancer cells that XIAP overexpression induces Akt phosphorylation/activation [11, 12]. Akt is activated by phosphorylation at threonine 308 and serine 473 in response to growth factors or cytokines [13–15] through phosphatidylinositol 3-kinase (PI 3-K). Once phosphorylated Akt has been shown to 1) phosphorylates and blocks the action of several pro-apoptotic proteins such as Bad , and 2) block cytochrome C release from the mitochondria through the regulation of Bcl-2 . The kinase Akt has been shown to induces phosphorylation of procaspase-9, suggesting that caspase processing and apoptosis can be directly regulated by protein phosphorylation . This is supported by the observation that an activated form of Akt is able to block apoptosis .
At the time of apoptosis induction Smac/DIABLO is released from mitochondria into the cytosol, where it binds to IAPs and enables caspase activation . It has been shown that Smac/DIABLO promotes not only the proteolytic activation of procaspase-3 but also the enzymatic activity of mature caspase-3, both of which depend upon its ability to interact physically with IAPs . Smac/DIABLO is synthesized with an N-terminal mitochondrial targeting sequence that is proteolytically removed during maturation to the mature polypeptide. X-ray crystallography has shown that the first four amino acids (AVPI) of mature Smac/DIABLO bind to a portion of the third BIR (BIR3) domain of XIAP . This N-terminal sequence is essential for binding IAPs and blocking their antiapoptotic effects .
Caspases are well known executioners of apoptosis. Once activated from their proactive forms, caspases target important proteins involved in cell proliferation and survival (for a review see ). Caspase-3 is one of the key executioner of apoptosis and induces downstream caspase-6 which in turn target cleavage of important structural proteins such as laminin and keratins [22, 23]. Among other caspase targets, poly(ADP-ribose) polymerase (PARP, 113–116 kDa), a nuclear enzyme which is activated during DNA damage, is known to be cleaved by caspases-3 and -7 . We have recently demonstrated that Akt is also a target for caspase-3 cleavage, indicating that Akt survival pathway inhibition is an important mechanism for apoptosis activation .
Although the regulation and importance of XIAP and Smac/DIABLO has been described in other systems and cell types, their expression has not been reported for the uterus. In the present study, we have investigated the regulation of XIAP, Smac/DIABLO, caspase-3, -6 and -7 during the four stages of estrous cycle (proestrus, estrus, metestrus and diestrus) and further analyses were carried out to determine the possible regulation of XIAP and Smac/DIABLO by 17β-estradiol in ovariectomized rats.
Materials and Methods
XIAP, Smac/DIABLO, NF-κB, IκB, Phospho-IκB and cleaved-caspases antibodies were obtained from New England Biolabs (Mississauga, ON). Vectastain ABC Kit for rabbit IgG was purchased from Vector Laboratories Inc. (Burlingame, CA). Protease Inhibitor Cocktail Tablets, POD and DAB substrate were purchased from Roche (Laval, QC). 17β-estradiol (E2) was purchased from Laboratoire Mat (Québec, QC).
Mature Sprague-Dawley female rats (200–225 g) were obtained from Charles River Laboratories Canada. Animals were maintained on standard chow and water, which were available ad libitum, in animal facilities illuminated on a normal 12 hour cycle. All procedures were performed in accordance with guidelines of the Canadian Council on Animal Care for the handling and training of laboratory animals and the Good Health and Animal Care Committee of the Université du Québec à Trois-Rivières. Stages of the estrous cycle were confirmed by vaginal smears. Rats with three regular cycles of 4 days were used in these experiments and killed at various stages of the estrous cycle (diestrus, proestrus, estrus and metestrus). Uteri were collected and fixed for immunohistochemical staining (IHC) or endometrial protein extracts collected by scraping the endometrium for Western analysis. To determine the effect of estrogen, rats were ovariectomized for at least 10 days and then injected with (17β-estradiol) E2. Animals were treated for a total of 3 days and killed after hormone treatment (72 hours) according to previous preliminary time-course studies done in our laboratory (Leblanc et al., unpublished information) and information found in the literature . E2 was dissolved with sesame oil, and administered by subcutaneous injection. Sesame oil was injected into control animals. The dose administered was 40 μg/kg/day (E2).
The uterus was fixed in 4% paraformaldehyde solution and embedded in paraffin. Tissue sections 7 μm thick were mounted on polylysine-coated slides, deparaffinized, rehydrated, and then heated with 10 mM citrate buffer (pH 6). After two wash with PBS, slides were then incubated with 0.3 % hydrogen peroxide in methanol for 30 min to quench endogenous peroxidase activity. After washing with PBS, tissues were incubated with blocking serum (Vectastain ABC Kit) at room temperature for 1 h. Then, a primary antibody (XIAP 1:200; Smac/DIABLO 1:100; and cleaved caspase-3 1:100) was added to the slides and incubated at 4°C overnight. After washing 5 min in PBS, tissue sections were incubated for 30 min with 3 μg/ml biotinylated antibody (anti-rabbit or anti-mouse). Subsequently, slides were washed with PBS and incubated with avidin-biotin complex reagent containing horseradish peroxidase for 30 min. Again washed with PBS for 5 min and colour development was achieved using DAB substrate. The tissue sections were counterstained with haematoxylin. Negative controls were performed using the same protocol without the presence of primary antibody.
Protein extraction and Western analysis
Endometrium from each uterus was scraped using a glass microscope slide and homogenized using a pipette in the lysis buffer (PBS 1X pH 7.4; 1% Nonidet P-40; 0.5% Sodium deoxycholate; 0.1% SDS; Protease Inhibitor Cocktail Tablets (Roche)). Homogenates were centrifuged (12,000 × g for 20 min at 4°C) to remove insoluble material. The supernatant was recovered and stored at -20°C pending analysis. Protein content was determined with the Bio-Rad DC Protein Assay. Concentrations of reagents found in the lysis buffer were chosen to avoid any interference with the protein assay. Protein extracts (50 μg) were heated at 94°C for 3 min, resolved by 10% SDS-PAGE and electrotransferred to nitrocellulose membranes using a semidry transfer (Bio-Rad, Mississauga, ON). The membranes were then blocked 2 h at room temperature with PBS containing 5 % milk powder, then incubated with XIAP 1:500; Smac/DIABLO 1:500; Caspase-3 1:1000; Caspase-6 1:1000; Caspase-7 1:1000; NF-κB 1:1000; IκB 1:1000; Phospho-IκB 1:500 and subsequently with horseradish peroxidase-conjugated anti-rabbit or anti-mouse secondary antibody (1:3000; room temperature for 45 min). All membranes were reprobed with a antibody specific to β-actin which was used as an internal standard. Densitometrical analyses were performed on both films (protein of interest and β-actin) using the GelDoc 2000 and the Quantity One software (Bio-Rad, Mississauga, ON). Results are expressed as a ratio protein of interest/β-actin to correct for loading for each endometrial sample.
Western analyses of cycling animals were repeated four to six times (one rat per extract/day repeated 4 to 6 different times). Endometrial extracts from each rats was assessed individually. Western blot analyses were performed with samples from ovariectomized rats treated with E2 (4 rats/group). Endometrial extracts from each rats was assessed individually for both studies. Results subjected to statistical analyses were expressed as means ± SEM. Data were subjected to one-way ANOVA (PRISM software version 4.0; GraphPad, San Diego, CA). Differences between experimental groups were determined by the Tukey's test. Statistical significance was accepted when P < 0.05.
Caspases activation during the estrous cycle
XIAP and Smac/DIABLO expression during the estrous cycle
Effect of 17β-estradiol on XIAP and Smac/DIABLO expression and caspases activation
NF-κB pathway regulation through the estrous cycle
We and other have demonstrated the presence of apoptosis in the rat [2, 3, 7] and mouse  endometrium during the estrous cycle. Although our recent study showed that regulation of Akt survival pathway is a key factor involved in the regulation of endometrial cell fate during estrous cycle , molecular and cellular mechanisms involved in the regulation of apoptosis in the uterus are poorly documented in the literature. Since menses are absent in rodent specie, there must be precise intra-cellular mechanisms involved in the regulation of cell fate in the endometrium after estrogen withdrawal in the absence of embryonic factors. We have previously demonstrated in human ovarian cancer cells  and rat granulosa cells  the importance of XIAP and Akt expression/activity. In the present study, regulation of XIAP and Smac/DIABLO have been investigated in rat uterus to determine their importance and their possible influence on endometrial cell survival/death in relation to the stage of estrous cycle.
In the present study, expression of XIAP was maximum at estrus and increased in response to E2 in ovariectomized rats. XIAP was strongly expressed in luminal and glandular epithelia and stroma during estrus, perhaps to protect these cells from apoptosis. Although stimulation of XIAP by E2 is consistent with mitogenic activity and apoptosis inhibitory activity, it is not clear why XIAP expression does not increase during proestrus. A recent study showed that XIAP may be directly regulated by the presence of tumor necrosis factor-α (TNF-α) in rat granulosa cells . Since it has been shown that TNF-α mRNA expression was high at estrus and was regulated by estrogen in the mouse uterus , a similar process may be involved in the endometrium. Thus, action of E2 on XIAP expression might be indirect and might involve specific factors regulated upstream and/or downstream by this hormone. Whether involvement of TNF-α or other growth factors/cytokines might be involved in this process remains to be elucidated.
In contrast, Smac/DIABLO was decreased at estrus and E2 treatment in ovariectomized rats reduced its expression. These results directly support the mitogenic action of estrogens on endometrial cells. Since Smac/DIABLO is a pro-apoptotic protein, its down-regulation may be sufficient to activate XIAP to inhibit caspase activity. Smac/DIABLO down-regulation also support our results obtained at estrus showing apoptosis predominantly in luminal epithelial cells  and suggest that this pro-apoptotic factor might have a key function in triggering apoptosis at this particular time of rat estrous cycle. There is currently no information available in the literature demonstrating that E2 modulates Smac/DIABLO expression and the present findings are the first to demonstrate this mechanism. E2treatment resulted in the cleavage of caspase-3, -6 and -7 in endometrial cells. This results was contradictory to the fact that E2 induces endometrial cells proliferation rather than inducing activation of the caspase cascade and apoptosis. Although it has been shown that E2triggers apoptosis in a preosteoclastic cell line in vitro  and in thymocytes of ovariectomized mice in vivo , it is unlikely that E2 induced apoptosis in the endometrium. This can be explained by the fact that following injection of ovariectomized rats with E2, latent endometrial cells are forced to proliferate and they might be in a situation of stress. Indeed, controlling the balance between survival and death factors is a key mechanism in order to maintain homeostasis in the proliferating endometrium. Increased caspase cleavage is not necessarily a sign of apoptosis activation; caspases activity can be blocked by the presence of high levels of XIAP (or other known or unknown inhibitor of apoptosis proteins such as cIAPs ) and the presence of low levels of Smac/DIABLO. This particular mechanism in endometrial cells might be important in order to rapidly induce apoptosis at the appropriate timing (at estrus for instance) through the simple inhibition or degradation of XIAP protein through its ubiquitin protein ligase activity its degradation in proteasomes in response to apoptotic stimuli .
Another explanation for the induction of caspase activation in response to E2 might be due to the presence and activity of E2 metabolites. For example, 2-Methoxyestradiol (2ME2), a natural metabolite of E2, is a potent antitumor and antiangiogenic agent  and has been shown to induce apoptosis is several cell type (for a review see ). Furthermore, 2ME2 is currently tested in clinical trials for cancer therapies . 2ME2 is a major metabolite of estradiol in human serum and its concentration peaks at mid-cycle, like that of estradiol . Studies have shown that 2ME2 acts through other signaling pathways than E2[38, 39]. A recent study revealed that 2ME2 treatment resulted in up-regulation of death receptor 5 (DR5) protein expression in vitro and in vivo and rendered cells more sensitive to the cytotoxic activities of the DR5 ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) . In addition, the latter study demonstrated that 2ME2-induced apoptosis required activation of caspase-8, caspase-9, and caspase-3 . Another recent study also showed induction of caspase-3 and apoptosis in response to 2ME2 in gastric carcinoma cells . These observation established in other systems and cell types suggest that 2ME2 could be an element of investigation in order to determine how E2 might be involved in the induction of caspase cleavage in rat endometrium and the possibility that activation of caspases observed might not be a direct action of E2.
Recent studies demonstrated that the transcriptional nuclear factor kappa-B (NF-κB) is a direct downstream target of phosphorylated Akt . NF-κB is sequestered (p65 and p50 subunits) in the cytoplasm by the IκBs inhibitors which are phosphorylation targets of Akt. Upon phosphorylation IκBs are released and degradated through ubiquitination and NF-κB enter nucleus for gene expression . In the literature, we found that XIAP promoter is a target for NF-κB [27, 28]. Since we have recently demonstrated the activation of Akt in response to 17β-estradiol in rat endometrium and that Akt has been shown to activate NF-κB signaling pathway , we wanted to know if Akt/ NF-κB/IκB pathway might be involved in the regulation of XIAP expression. Results of the present study showed that there was no difference in the expression of NF-κB and IκB nor IκB phosphorylation during the four stages of estrous cycle which exclude the involvement of this pathway in the regulation of XIAP or Smac/DIABLO expression. Other pathways downstream of Akt known to be regulated by this kinase are currently investigated in our laboratory such as eNOS [44, 45], Bad , glycogen synthase kinase 3β (GSK-3β) [47, 48], and caspase-9 . A recent report further demonstrated that insulin-like growth factor-1 (IGF-1) induced activation of Akt, NF-κB and induced phosphorylation of Forkhead transcription factor (FKHR), which in turn up-regulated a series of intracellular anti-apoptotic proteins such as XIAP . Because, FKHR is also a well known target for Akt action , phosphorylation, activity and regulation of this transcription factor in the uterus needs to be investigated.
In conclusion, the present study showed for the first time the presence and regulation of XIAP and Smac/DIABLO in the rat endometrium and further demonstrated that these two survival factors are regulated in the opposite direction by E2. Further analysis will be necessary to determine more specifically, the intra-cellular and molecular signal transducers involved in the process of apoptosis in the rat reproductive tract and to determine the mechanism by which XIAP and Smac/DIABLO are regulated.
This work has been supported by a grant from NSERC (238501-01). Eric Asselin is a recipient of a fellowship from the Fonds de la Recherche en Santé du Québec (FRSQ). We are grateful to Mrs Rollande Caron who brought a lot technical expertise with animals and gave plenty of her precious time for these studies.
- Dharma SJ, Kholkute SD, Nandedkar TD: Apoptosis in endometrium of mouse during estrous cycle. Indian J Exp Biol. 2001, 39: 218-222.PubMedGoogle Scholar
- Lai MD, Lee LR, Cheng KS, Wing LY: Expression of proliferating cell nuclear antigen in luminal epithelium during the growth and regression of rat uterus. J Endocrinol. 2000, 166: 87-93.View ArticlePubMedGoogle Scholar
- Sato T, Fukazawa Y, Kojima H, Enari M, Iguchi T, Ohta Y: Apoptotic cell death during the estrous cycle in the rat uterus and vagina. Anat Rec. 1997, 248: 76-83. 10.1002/(SICI)1097-0185(199705)248:1<76::AID-AR9>3.3.CO;2-G.View ArticlePubMedGoogle Scholar
- Quarmby VE, Korach KS: The influence of 17 beta-estradiol on patterns of cell division in the uterus. Endocrinology. 1984, 114: 694-702.View ArticlePubMedGoogle Scholar
- Finn CA, Publicover M: Hormonal control of cell death in the luminal epithelium of the mouse uterus. J Endocrinol. 1981, 91: 335-340.View ArticlePubMedGoogle Scholar
- Martin L, Pollard JW, Fagg B: Oestriol, oestradiol-17beta and the proliferation and death of uterine cells. J Endocrinol. 1976, 69: 103-115.View ArticlePubMedGoogle Scholar
- Dery MC, Leblanc V, Shooner C, Asselin E: Regulation of Akt expression and phosphorylation by 17beta-estradiol in the rat uterus during estrous cycle. Reprod Biol Endocrinol. 2003, 1: 47-10.1186/1477-7827-1-47.PubMed CentralView ArticlePubMedGoogle Scholar
- Deveraux QL, Takahashi R, Salvesen GS, Reed JC: X-linked IAP is a direct inhibitor of cell-death proteases. Nature. 1997, 388: 300-304. 10.1038/40901.View ArticlePubMedGoogle Scholar
- Takahashi R, Deveraux Q, Tamm I, Welsh K, Assa-Munt N, Salvesen GS, Reed JC: A single BIR domain of XIAP sufficient for inhibiting caspases. J Biol Chem. 1998, 273: 7787-7790. 10.1074/jbc.273.14.7787.View ArticlePubMedGoogle Scholar
- LaCasse EC, Baird S, Korneluk RG, Mackenzie AE: The inhibitors of apoptosis (IAPs) and their emerging role in cancer. Oncogene. 1998, 17: 3247-3259. 10.1038/sj.onc.1202569.View ArticlePubMedGoogle Scholar
- Asselin E, Wang Y, Tsang BK: X-linked inhibitor of apoptosis protein activates the phosphatidylinositol 3-kinase/Akt pathway in rat granulosa cells during follicular development. Endocrinology. 2001, 142: 2451-2457. 10.1210/en.142.6.2451.PubMedGoogle Scholar
- Asselin E, Mills GB, Tsang BK: XIAP regulates Akt activity and caspase-3-dependent cleavage during cisplatin-induced apoptosis in human ovarian epithelial cancer cells. Cancer Res. 2001, 61: 1862-1868.PubMedGoogle Scholar
- Stephens L, Anderson K, Stokoe D, Erdjument-Bromage H, Painter GF, Holmes AB, Gaffney PR, Reese CB, McCormick F, Tempst P, Coadwell J, Hawkins PT: Protein kinase B kinases that mediate phosphatidylinositol 3,4,5-trisphosphate-dependent activation of protein kinase B. Science. 1998, 279: 710-714. 10.1126/science.279.5351.710.View ArticlePubMedGoogle Scholar
- Hayakawa J, Ohmichi M, Kurachi H, Kanda Y, Hisamoto K, Nishio Y, Adachi K, Tasaka K, Kanzaki T, Murata Y: Inhibition of BAD phosphorylation either at serine 112 via extracellular signal-regulated protein kinase cascade or at serine 136 via Akt cascade sensitizes human ovarian cancer cells to cisplatin. Cancer Res. 2000, 60: 5988-5994.PubMedGoogle Scholar
- Suzuki Y, Nakabayashi Y, Takahashi R: Ubiquitin-protein ligase activity of X-linked inhibitor of apoptosis protein promotes proteasomal degradation of caspase-3 and enhances its anti-apoptotic effect in Fas-induced cell death. Proc Natl Acad Sci U S A. 2001, 98: 8662-8667. 10.1073/pnas.161506698.PubMed CentralView ArticlePubMedGoogle Scholar
- Davies MA, Koul D, Dhesi H, Berman R, McDonnell TJ, McConkey D, Yung WK, Steck PA: Regulation of Akt/PKB activity, cellular growth, and apoptosis in prostate carcinoma cells by MMAC/PTEN. Cancer Res. 1999, 59: 2551-2556.PubMedGoogle Scholar
- Cardone MH, Roy N, Stennicke HR, Salvesen GS, Franke TF, Stanbridge E, Frisch S, Reed JC: Regulation of cell death protease caspase-9 by phosphorylation. Science. 1998, 282: 1318-1321. 10.1126/science.282.5392.1318.View ArticlePubMedGoogle Scholar
- Kennedy SG, Wagner AJ, Conzen SD, Jordan J, Bellacosa A, Tsichlis PN, Hay N: The PI 3-kinase/Akt signaling pathway delivers an anti-apoptotic signal. Genes Dev. 1997, 11: 701-713.View ArticlePubMedGoogle Scholar
- Chai J, Du C, Wu JW, Kyin S, Wang X, Shi Y: Structural and biochemical basis of apoptotic activation by Smac/DIABLO. Nature. 2000, 406: 855-862. 10.1038/35022514.View ArticlePubMedGoogle Scholar
- Liu Z, Sun C, Olejniczak ET, Meadows RP, Betz SF, Oost T, Herrmann J, Wu JC, Fesik SW: Structural basis for binding of Smac/DIABLO to the XIAP BIR3 domain. Nature. 2000, 408: 1004-1008. 10.1038/35050006.View ArticlePubMedGoogle Scholar
- Cohen GM: Caspases: the executioners of apoptosis. Biochem J. 1997, 326: 1-16.PubMed CentralView ArticlePubMedGoogle Scholar
- Prasad SC, Thraves PJ, Kuettel MR, Srinivasarao GY, Dritschilo A, Soldatenkov VA: Apoptosis-associated proteolysis of vimentin in human prostate epithelial tumor cells. Biochem Biophys Res Commun. 1998, 249: 332-338. 10.1006/bbrc.1998.9137.View ArticlePubMedGoogle Scholar
- Caulin C, Salvesen GS, Oshima RG: Caspase cleavage of keratin 18 and reorganization of intermediate filaments during epithelial cell apoptosis. J Cell Biol. 1997, 138: 1379-1394. 10.1083/jcb.138.6.1379.PubMed CentralView ArticlePubMedGoogle Scholar
- Nicholson DW, Ali A, Thornberry NA, Vaillancourt JP, Ding CK, Gallant M, Gareau Y, Griffin PR, Labelle M, Lazebnik YA, .: Identification and inhibition of the ICE/CED-3 protease necessary for mammalian apoptosis. Nature. 1995, 376: 37-43. 10.1038/376037a0.View ArticlePubMedGoogle Scholar
- Nephew KP, Ray S, Hlaing M, Ahluwalia A, Wu SD, Long X, Hyder SM, Bigsby RM: Expression of estrogen receptor coactivators in the rat uterus. Biol Reprod. 2000, 63: 361-367.View ArticlePubMedGoogle Scholar
- Datta SR, Brunet A, Greenberg ME: Cellular survival: a play in three Akts. Genes Dev. 1999, 13: 2905-2927. 10.1101/gad.13.22.2905.View ArticlePubMedGoogle Scholar
- Xiao CW, Ash K, Tsang BK: Nuclear factor-kappaB-mediated X-linked inhibitor of apoptosis protein expression prevents rat granulosa cells from tumor necrosis factor alpha-induced apoptosis. Endocrinology. 2001, 142: 557-563. 10.1210/en.142.2.557.PubMedGoogle Scholar
- Stehlik C, de Martin R, Kumabashiri I, Schmid JA, Binder BR, Lipp J: Nuclear factor (NF)-kappaB-regulated X-chromosome-linked iap gene expression protects endothelial cells from tumor necrosis factor alpha-induced apoptosis. J Exp Med. 1998, 188: 211-216. 10.1084/jem.188.1.211.PubMed CentralView ArticlePubMedGoogle Scholar
- Steffan NM, Bren GD, Frantz B, Tocci MJ, O'Neill EA, Paya CV: Regulation of IkB alpha phosphorylation by PKC- and Ca(2+)-dependent signal transduction pathways. J Immunol. 1995, 155: 4685-4691.PubMedGoogle Scholar
- De M, Sanford TR, Wood GW: Interleukin-1, interleukin-6, and tumor necrosis factor alpha are produced in the mouse uterus during the estrous cycle and are induced by estrogen and progesterone. Dev Biol. 1992, 151: 297-305.View ArticlePubMedGoogle Scholar
- Zecchi-Orlandini S, Formigli L, Tani A, Benvenuti S, Fiorelli G, Papucci L, Capaccioli S, Orlandini GE, Brandi ML: 17beta-estradiol induces apoptosis in the preosteoclastic FLG 29.1 cell line. Biochem Biophys Res Commun. 1999, 255: 680-685. 10.1006/bbrc.1999.0215.View ArticlePubMedGoogle Scholar
- Patel H, Hoffman-Goetz L: Effects of oestrogen and exercise on caspase-3 activity in primary and secondary lymphoid compartments in ovariectomized mice. Acta Physiol Scand. 2002, 176: 177-184. 10.1046/j.1365-201X.2002.01033.x.View ArticlePubMedGoogle Scholar
- Gagnon V, St-Germain ME, Parent S, Asselin E: Akt activity in endometrial cancer cells: regulation of cell survival through cIAP-1. Int J Oncol. 2003, 23: 803-810.PubMedGoogle Scholar
- Yang Y, Fang S, Jensen JP, Weissman AM, Ashwell JD: Ubiquitin protein ligase activity of IAPs and their degradation in proteasomes in response to apoptotic stimuli. Science. 2000, 288: 874-877. 10.1126/science.288.5467.874.View ArticlePubMedGoogle Scholar
- Pribluda VS, Gubish E.R.,Jr., LaVallee TM, Treston A, Swartz GM, Green SJ: 2-Methoxyestradiol: an endogenous antiangiogenic and antiproliferative drug candidate. Cancer Metastasis Rev. 2000, 19: 173-179. 10.1023/A:1026543018478.View ArticlePubMedGoogle Scholar
- Schumacher G, Neuhaus P: The physiological estrogen metabolite 2-methoxyestradiol reduces tumor growth and induces apoptosis in human solid tumors. J Cancer Res Clin Oncol. 2001, 127: 405-410. 10.1007/s004320000233.View ArticlePubMedGoogle Scholar
- Berg D, Sonsalla R, Kuss E: Concentrations of 2-methoxyoestrogens in human serum measured by a heterologous immunoassay with an 125I-labelled ligand. Acta Endocrinol (Copenh). 1983, 103: 282-288.Google Scholar
- Dubey RK, Jackson EK, Keller PJ, Imthurn B, Rosselli M: Estradiol metabolites inhibit endothelin synthesis by an estrogen receptor-independent mechanism. Hypertension. 2001, 37: 640-644.View ArticlePubMedGoogle Scholar
- Dubey RK, Gillespie DG, Zacharia LC, Rosselli M, Korzekwa KR, Fingerle J, Jackson EK: Methoxyestradiols mediate the antimitogenic effects of estradiol on vascular smooth muscle cells via estrogen receptor-independent mechanisms. Biochem Biophys Res Commun. 2000, 278: 27-33. 10.1006/bbrc.2000.3755.View ArticlePubMedGoogle Scholar
- LaVallee TM, Zhan XH, Johnson MS, Herbstritt CJ, Swartz G, Williams MS, Hembrough WA, Green SJ, Pribluda VS: 2-methoxyestradiol up-regulates death receptor 5 and induces apoptosis through activation of the extrinsic pathway. Cancer Res. 2003, 63: 468-475.PubMedGoogle Scholar
- Lin HL, Liu TY, Wu CW, Chi CW: 2-Methoxyestradiol-induced caspase-3 activation and apoptosis occurs through G(2)/M arrest dependent and independent pathways in gastric carcinoma cells. Cancer. 2001, 92: 500-509. 10.1002/1097-0142(20010801)92:3<500::AID-CNCR1348>3.0.CO;2-4.View ArticlePubMedGoogle Scholar
- Kane LP, Shapiro VS, Stokoe D, Weiss A: Induction of NF-kappaB by the Akt/PKB kinase. Curr Biol. 1999, 9: 601-604. 10.1016/S0960-9822(99)80265-6.View ArticlePubMedGoogle Scholar
- Foo SY, Nolan GP: NF-kappaB to the rescue: RELs, apoptosis and cellular transformation. Trends Genet. 1999, 15: 229-235. 10.1016/S0168-9525(99)01719-9.View ArticlePubMedGoogle Scholar
- Dimmeler S, Fleming I, Fisslthaler B, Hermann C, Busse R, Zeiher AM: Activation of nitric oxide synthase in endothelial cells by Akt-dependent phosphorylation. Nature. 1999, 399: 601-605. 10.1038/21224.View ArticlePubMedGoogle Scholar
- Fulton D, Gratton JP, McCabe TJ, Fontana J, Fujio Y, Walsh K, Franke TF, Papapetropoulos A, Sessa WC: Regulation of endothelium-derived nitric oxide production by the protein kinase Akt. Nature. 1999, 399: 597-601. 10.1038/21218.PubMed CentralView ArticlePubMedGoogle Scholar
- Pastorino JG, Tafani M, Farber JL: Tumor necrosis factor induces phosphorylation and translocation of BAD through a phosphatidylinositide-3-OH kinase-dependent pathway. J Biol Chem. 1999, 274: 19411-19416. 10.1074/jbc.274.27.19411.View ArticlePubMedGoogle Scholar
- Pap M, Cooper GM: Role of glycogen synthase kinase-3 in the phosphatidylinositol 3-Kinase/Akt cell survival pathway. J Biol Chem. 1998, 273: 19929-19932. 10.1074/jbc.273.32.19929.View ArticlePubMedGoogle Scholar
- van Weeren PC, de Bruyn KM, Vries-Smits AM, van Lint J, Burgering BM: Essential role for protein kinase B (PKB) in insulin-induced glycogen synthase kinase 3 inactivation. Characterization of dominant-negative mutant of PKB. J Biol Chem. 1998, 273: 13150-13156. 10.1074/jbc.273.21.13150.View ArticlePubMedGoogle Scholar
- Zhou H, Li XM, Meinkoth J, Pittman RN: Akt regulates cell survival and apoptosis at a postmitochondrial level. J Cell Biol. 2000, 151: 483-494. 10.1083/jcb.151.3.483.PubMed CentralView ArticlePubMedGoogle Scholar
- Mitsiades CS, Mitsiades N, Poulaki V, Schlossman R, Akiyama M, Chauhan D, Hideshima T, Treon SP, Munshi NC, Richardson PG, Anderson KC: Activation of NF-kappaB and upregulation of intracellular anti-apoptotic proteins via the IGF-1/Akt signaling in human multiple myeloma cells: therapeutic implications. Oncogene. 2002, 21: 5673-5683. 10.1038/sj.onc.1205664.View ArticlePubMedGoogle Scholar
- Brunet A, Bonni A, Zigmond MJ, Lin MZ, Juo P, Hu LS, Anderson MJ, Arden KC, Blenis J, Greenberg ME: Akt promotes cell survival by phosphorylating and inhibiting a Forkhead transcription factor. Cell. 1999, 96: 857-868.View ArticlePubMedGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original URL.