- Open Access
Involvement of cyclin B1 in progesterone-mediated cell growth inhibition, G2/M cell cycle arrest, and apoptosis in human endometrial cell
- Li Tang†1, 4,
- Yu Zhang†1,
- Hong Pan1,
- Qiong Luo1,
- Xiao-Ming Zhu1,
- Min-Yue Dong1,
- Peter CK Leung3,
- Jian-Zhong Sheng2Email author and
- He-Feng Huang1Email author
© Tang et al; licensee BioMed Central Ltd. 2009
Received: 16 October 2009
Accepted: 7 December 2009
Published: 7 December 2009
Progesterone plays an important role in the proliferation and differentiation of human endometrial cells (hECs). Large-dose treatment with progesterone has been used for treatment of endometrial proliferative disorders. However, the mechanisms behind remain unknown.
To investigate the role of cyclin B1 in proliferation and differentiation of hECs in menstrual cycle, the expression of cyclin B1 throughout the menstrual cycle was evaluated in hECs. To determine the effects of progesterone on the proliferation, cell cycle progression and apoptosis of hECs and to test if cyclin B1 is involved in these effects, progesterone and/or Alsterpaullone (Alp, a specific inhibitor of Cyclin B1/Cdc2) were added to primary hECs. Cellular proliferation was evaluated with MTT test, cell cycle with propidium iodide (PI) staining and flow cytometry, apoptosis with FITC-Annexin V and the expression of cyclin B1 with Western blotting.
The expression level of cyclin B1 in secretory endometria was significantly lower than in proliferative endometria (p < 0.01). Progesterone significantly inhibited the growth of hECs in a concentration-dependent manner (P < 0.01). The treatment with progesterone significantly decreased the expression of cyclin B1, increased the proportions of cell in G2/M phase, and apoptotic cells (P < 0.05 for all). The presence of Alp significantly enhanced the effects of progesterone on cyclin B1 down-regulation, G2/M cell cycle arrest and induction of apoptosis (P < 0.01 for all).
Our findings suggest that cyclin B1 is a critical factor in proliferation and differentiation of hECs. Progesterone may inhibit cell proliferation, mediate G2/M cell cycle arrest and induce apoptosis in hECs via down-regulating Cyclin B1.
Progesterone plays a pivotal role in female reproduction. It modifies the effects of estrogen on the endometrium. Estrogen stimulates proliferation of both glandular epithelial cells and stromal cells, whereas progesterone prevents this effect and induces secretory changes in glandular epithelial cells and decidual changes in stromal cells. The balance between these two hormones plays important roles in regulation of the menstrual cycle, ovulation, implantation and pregnancy.
The potent anti-proliferative effect of progesterone has been utilized for treatment of endometrial proliferative disorders. Clinically, progesterone has been used for contraception and the treatment of endometrial hyperplasia and adenocarcinoma as well as endometriosis [4–6]. It is known that long term and large dose treatment with progesterone analogs may lead to the limitation of endometrial growth, atrophy, apoptosis and even cell death. Therapeutic use of progesterone is often associated with irregular and unwanted bleeding. Recent clinical studies have also raised concern about an increased risk of cardiovascular disease or breast cancer. It highlights the importance of insights from molecular biology of progesterone action on endometrium which may provide us with more precise markers for progesterone actions and thus help avoid side-effects and lead to new therapeutic proposal.
Previous studies have shown that progesterone regulates endometrial cell proliferation and differentiation through a nuclear receptor-mediated mechanism, such as down-regulation of estrogen receptor[9, 10]. The progesterone-induced growth suppression of endometrial cells has also been explained in various ways such as the elevated activity of steroid metabolizing enzymes, growth factors and cytokines. However, the underlying molecular mechanisms by which progesterone negatively regulates the growth of endometrial cells are still not fully understood.
Cell proliferation is restrained through the control of the cell cycle. Cyclin B1 is the key component of the cell cycle machinery. Cyclin B1 binds to Cdc2 at the beginning of G2 phase forming an activated cyclin B1/Cdc2 complex and then phosphorylates its downstream substrates which control the G2 to M transition and promote cell mitotic division. Unscheduled mis-regulation of cyclin B1 during the cell cycle leads to uncontrolled cell growth and aberrant cell function. It is also reported that cyclins are functionally involved in the rhythmic proliferation of normal human endometrial tissue. Moreover, upregulated expression of cyclin B1, cyclin D1 and cyclin E was detected in endometrial carcinomas, which indicated that cyclins might be the major cell cycle regulators involved in endometrial cell proliferation and differentiation. Up to date, it is still unclear whether cyclins are mediated in the negative regulation of the endometrium by progesterone.
As the detection of significantly down-regulated expression of cyclin B1 in secretory endometria strongly suggests that cyclin B1 plays an important role in proliferation and differentiation of hECs under steroids regulation, we then examined the effects of progesterone on the proliferation, cell cycle progression and apoptosis of hECs and tested if cyclin B1 is involved in these effects. In addition, we determined whether Alsterpaullone (Alp, a specific inhibitor of Cyclin B1/Cdc2) is capable of enhancing the effects of progesterone on cyclin B1 down-regulation, G2/M cell cycle arrest and induction of apoptosis.
Endometrial tissues were obtained from 18 women (at proliferative phase) who underwent hysterectomy or hysteroscopy and 12 women (at middle secretory phase) who underwent aspiration biopsy during IVF program for benign uterine diseases in Women's Hospital, School of Medicine, Zhejiang University. Written informed consents were obtained from all subjects and the Institutional Review Board of School of Medicine, Zhejiang University, granted the ethical approval for the current investigation. All the women had regular menstrual cycles and received no hormonal treatments three months prior to the operation. Their ages ranged from 29 to 47 years. The menstrual cycle phase was confirmed by histologic dating.
6 cases of endometrial tissue at proliferative phase were minced in Hanks' solution and digested with 0.2% collagenase (Gibco-BRL, Gaithersburg, MD, USA) at 37°C for 50 min. The dispersed cells were filtered through a 70-mm nylon mesh to remove the undigested tissue pieces. Cells, containing endometrial epithelial cells and endometrial stromal cells were collected and re-suspended in Dulbecco's modified Eagle's medium (DMEM, Gibco-BRL) supplemented with 10% fetal bovine serum (Invitrogen), 50 U/ml penicillin, and 50 μg/ml streptomycin in a 60-mm or 10-mm petri dish or 24 well plate in a humidified atmosphere of 5% CO2 at 37°C. The medium was changed every day. Progesterone at the concentration of 1 × 10-9, 1 × 10-8, 1 × 10-7 or 1 × 10-6 M or progesterone (1 × 10-7 M) and/or Alp (5 mM) (Calbiochem, USA) was added and the cells were incubated for another 72 h before specific experiments. Each experiment was repeated at least three times.
MTT (3- [4, 5-dimethylthiazol-2-yl]-2, 5-diphenyl tetrazolium bromide) assay was used to evaluate the cellular proliferation. Briefly, after hECs were treated with progesterone for 72 h, 20 μl of MTT (5 mg/ml) (Sigma, USA) was added and the cells were incubated for additional 4 h at 37°C. When the incubation finished, 200 μl of Dimethyl sulfoxide (DMSO) was added and the optical densities (OD) were read at 490 nm with a microplate reader. The experiment was conducted in triplicate and repeated three times. Inhibition rate was calculated as following: (1-OD sample/OD control) × 100%.
Cell cycle analysis
Cells were detached by trypsinization, washed three times with cold PBS and fixed with 80% ethanol at 4°C for 3 h. For propidium iodide (PI) staining, cells were washed three times with PBS to remove trace ethanol. The pellets were re-suspended and stained with propidium iodide (PI) (Sigma, USA)staining solution (0.1 mg PI and 0.5 mg/ml RNase A in PBS) and incubated at 37°C for 30 min. Cells were analyzed with flow cytometry FACS EPICS (Coulter Epics Altra flow cytometer; Beckman Coulter, Fullerton, CA).
Detection of apoptotic cells
Cells were detached, washed and re-suspended in 200 μl medium and fluorescently labeled by addition of 20 μl of binding buffer and 5 μl of Annexin V-FITC (Pharmingen, SanDiego, CA). After the incubation at room temperature in dark for 15 min, 2 μl of PI (1 mg/mL, Invitrogen, USA) was added and cells were applied to flow cytometry (Coulter Epics Altra flow cytometer). A minimum of 10,000 cells with in the gated region was analyzed.
Protein extraction and Western blot analysis
Tissues and cells were washed with PBS and lysed in lysis buffer (1× PBS, 1% Nonidet P-40, 0.5% sodium deoxycholate, 0.1% SDS, 100 μg/ml phenylmethylsulfonyl fluoride, 100 μg/ml leupeptin). The suspension was centrifuged at 15,000 g for 15 min at 4°C, the supernatant was collected and protein concentrations were determined using the Bradford method. 30 μg of protein per lane was loaded and separated on a 10% Sodium dodecylsulfate (SDS)-polyacrylamide gel and transferred to Nitrocellulose Transfer membrane (PROTRAN, BioScience, Germany). Membranes were incubated with blocking buffer (50 mM Tris-HCl, pH 7.6, 150 mM NaCl, 0.1% Tween 20 containing 5% non-fat milk) for 1 h, and then incubated with monoclonal mouse anti-human Cyclin B1 antibody (Santa Cruz Biotechnology, CA, USA, 1:200 dilution), polyclonal goat anti-human β-actin antibody (Santa Cruz Biotechnology, 1:2000 dilution) in blocking buffer overnight at 4°C. Then membranes were incubated with appropriate secondary antibody for 1 h at room temperature. The bound antibody was detected using an enhanced chemilumiscent (ECL) detection reagent (Santa Cruz Biotechnology) and the bands were scanned by Quantity One software (Bio-Rad Laboratories, Hercules, CA, USA). Normalized densities were determined with ratio of density of cyclin B1 to that of β-actin.
All data were presented as mean ± SD. Student's t-test or One-way analysis of variance (ANOVA) were used to compare means. A P value less than 0.05 were considered statistically significant.
Expression of cyclin B1 in human endometrium
Progesterone inhibits growth of hECs
Progesterone and/or Alp decreases the expression of cyclin B1
Progesterone or plus Alp mediate cell cycle arrest at G2/M stage
Progesterone or plus Alp induce apoptosis of hEC
In the present study, we demonstrated that the expression level of cyclin B1 in secretory endometria was significantly lower than in proliferative endometria. Progesterone inhibited the growth of hECs in a concentration-dependent manner. The treatment with progesterone significantly decreased the expression of cyclin B1, increased the proportions of cell in G2/M phase, and apoptotic cells. In addition, the presence of Alp enhanced the effects of progesterone on cyclin B1 down-regulation, G2/M cell cycle arrest and induction of apoptosis. Our results indicated that cyclinB1 played an important role in the endometrial cell cycle progression regulated by progesterone.
Cyclin B1, the master regulator in cell proliferation, plays an essential role in G2/M transition of mitosis in cell proliferation[19, 20]. They are functionally involved in the rhythmic proliferation and differentiation of human endometrium and their actions are related to the levels of sex steroids in endometrium. Our experimental data confirmed the result of previous study that CyclinB1/Cdc2 was expressed in proliferating cells of the normal endometrium, and the expression of these molecules were suppressed in the secretory phase. As the menstrual cycle is controlled by the sex steroids, mainly estrogen and progesterone, we speculated that the down-regulated expression of cyclin B1 in secretory endometrium is induced, at least partly, by the ascendant secretion of progesterone.
In vitro primary hECs culture confirmed the anti-proliferative effect of progesterone in endometrial cell. Our data showed that low dose of progesterone had no evident effect on the proliferation of hECs, but high dose of physiological level (10-7 M)  and an even higher level (10-6 M) could significantly inhibit the hECs proliferation. It is consistent with clinical application of large dose progesterone in treatment for endometrial proliferative disorders. As abundant expression of Cyclin B1 and alteration of the G2 pathway was reported in abnormal proliferative endometrial tissues, such as endometrial hyperplasia, endometrial adenocarcinoma and endometriosis[16, 18, 19, 22–24] the down-regulation of cyclin B1 detected under the treatment of progesterone could well explain the underlying mechanism of the inhibitory effect of progesterone on endometrial cell growth.
A few previous studies reported that the growth inhibitory effect of progesterone in endometrial cell was induced by the enhancement of cell cycle arrest at the G1/S phase[25, 26]. Recently, microarray analysis of progesterone effects on endometrial cell done by Paulssen et al indicated the significantly down-regulation of cyclin B1. In these studies, either mice endometrial epithelial cell or human endometrial epithelial cancer cell line, Ishikawa cells, were used as cell model. In the current study, we used human primary endometrial cell for the treatment of progesterone, it was more close to the human physiology. Flow cytometry results showed that progesterone acted on cell cycle progression by regulating G2/M transition in hECs with the down-regulation of cyclin B1. We supposed that some of the different findings were due to the different cell models and progesterone types and doses used in the separate experiments. Results from primary human endometrial cell culture with physiological high level progesterone treatment in our experiment provided new evidence of the underlying mechanism.
It is considered that endometrium apoptosis was regulated by hormonal changes. In the present study, apoptosis was observed in cultured hECs and the number of apoptotic cells was increased by the stimulation of progesterone, indicating high level progesterone induces apoptosis of endometrial cells. As G2/M arrest and apoptosis are common phenomena after genetic damage of the G2 pathway, we speculated that the induction of apoptosis in hECs by progesterone was also conducted by down-regulation of cyclin B1. This might be one of the mechanisms of anti-proliferation and endometrial atrophy induction in women who receives large dose progesterone treatment for endometrial proliferative disorders.
The activity of cyclinB1 could be inactivated by its inhibitors, resulting in cell cycle arrest. CyclinB1/cdc2 inhibitors, such as Camptothecin and Paclitaxel, have been used for the treatment of malignancies and have been demonstrated to be effective in limiting tumor cell growth by down-regulation of cyclinB1/cdc2[29–32]. Alsterpaullone (Alp) is a specific inhibitor of cyclin B1/cdc2, which inactivates cyclin B1/cdc2 complex and results in the arrest of cell growth by competitively inhibiting ATP to combine with the catalytic domain of cdc2[29, 33]. Our results showed that the presence of Alp significantly enhanced the effects of progesterone on cyclin B1 down-regulation, G2/M cell cycle arrest and induction of apoptosis. It further confirmed the pivotal role of cyclin B1 in the progesterone active pathway in hECs. Previous studies showed that although Alp alone induced cell arrest at G2/M phase, the proportion was only 2-fold higher than control. In the present study, the proportion of the G2/M cell cycle arrest induced by progesterone plus Alp was around 9-fold higher than control and 2.5-fold higher than progesterone only. The proportion of endometrial cell apoptosis induced by progesterone plus Alp was 12-fold higher than control and 3-fold higher than progesterone only. Our results suggest that Alp could enhance the inhibitory effect of progesterone on endometrial cell growth and apoptosis. Although further study is needed to clarify the mechanisms involved in these effects by Alp, these findings implicated that use of progesterone together with ingredient of cell cycle inhibitors might improve the therapeutic effect of hyperplasia, adenocarcinoma of endometrium and endometriosis. It will be interesting to validate this conjecture in the further research.
In conclusion, progesterone may inhibit cell proliferation, mediate G2/M cell cycle arrest and induce apoptosis in hECs via down-regulating Cyclin B1. The presence of Alp enhanced the effects of progesterone on cyclin B1 down-regulation, G2/M cell cycle arrest and induction of apoptosis. Our findings suggest that cyclin B1 is a critical factor in proliferation and differentiation of hECs. Progesterone derivatives in combination with ingredient of CyclinB1 inhibitors may be a promising way for the treatment of endometrial proliferative diseases. Future investigations targeting the progesterone pathway on aberrant endometrial cell may be fruitful for developing a novel proposal of progesterone treatment.
We would like to give our thanks to Cai-yun Zhou for technical assistance. This work was supported by National Basic Research Program of China (No.973: 2006CB944006 and 2006CB504004).
- Druckmann R: Long-term use of progestogens--getting the balance right: molecular biology and the endometrium. Gynecol Endocrinol. 2007, 23 (Suppl 1): 53-61. 10.1080/09513590701585045.View ArticlePubMedGoogle Scholar
- Strausfeld U, Labbe JC, Fesquet D, Cavadore JC, Picard A, Sadhu K, Russell P, Doree M: Dephosphorylation and activation of a p34cdc2/cyclin B complex in vitro by human CDC25 protein. Nature. 1991, 351: 242-245. 10.1038/351242a0.View ArticlePubMedGoogle Scholar
- Lindahl B, Willen R: Endometrial hyperplasia. Clinico-pathological considerations of a prospective randomised study after abrasio only or high-dose gestagen treatment. Results of 2 years follow-up of 292 patients. Anticancer Res. 1991, 11: 403-406.PubMedGoogle Scholar
- Randall TC, Kurman RJ: Progestin treatment of atypical hyperplasia and well-differentiated carcinoma of the endometrium in women under age 40. Obstet Gynecol. 1997, 90: 434-440. 10.1016/S0029-7844(97)00297-4.View ArticlePubMedGoogle Scholar
- Thigpen JT, Brady MF, Alvarez RD, Adelson MD, Homesley HD, Manetta A, Soper JT, Given FT: Oral medroxyprogesterone acetate in the treatment of advanced or recurrent endometrial carcinoma: a dose-response study by the Gynecologic Oncology Group. J Clin Oncol. 1999, 17: 1736-1744.PubMedGoogle Scholar
- Vereide AB, Arnes M, Straume B, Maltau JM, Orbo A: Nuclear morphometric changes and therapy monitoring in patients with endometrial hyperplasia: a study comparing effects of intrauterine levonorgestrel and systemic medroxyprogesterone. Gynecol Oncol. 2003, 91: 526-533. 10.1016/j.ygyno.2003.07.002.View ArticlePubMedGoogle Scholar
- Phillips V, Graham CT, Manek S, McCluggage WG: The effects of the levonorgestrel intrauterine system (Mirena coil) on endometrial morphology. J Clin Pathol. 2003, 56: 305-307. 10.1136/jcp.56.4.305.PubMed CentralView ArticlePubMedGoogle Scholar
- Hapgood JP, Koubovec D, Louw A, Africander D: Not all progestins are the same: implications for usage. Trends Pharmacol Sci. 2004, 25: 554-557. 10.1016/j.tips.2004.09.005.View ArticlePubMedGoogle Scholar
- Fujishita A, Nakane PK, Koji T, Masuzaki H, Chavez RO, Yamabe T, Ishimaru T: Expression of estrogen and progesterone receptors in endometrium and peritoneal endometriosis: an immunohistochemical and in situ hybridization study. Fertil Steril. 1997, 67: 856-864. 10.1016/S0015-0282(97)81397-0.View ArticlePubMedGoogle Scholar
- Nishimura R, Saeki T, Ohsumi S, Tani Y, Takashima S: Immunohistochemical expression of hormone receptors and the histological characteristics of biochemically hormone receptor negative breast cancers. Breast Cancer. 2007, 14: 100-104. 10.2325/jbcs.14.100.View ArticlePubMedGoogle Scholar
- Gein SV, Baeva TA, Kichanova OA: Effect of beta-endorphin on production of antibodies and IL-4 under conditions of opioid receptor blockade. Bull Exp Biol Med. 2006, 142: 226-229. 10.1007/s10517-006-0334-6.View ArticlePubMedGoogle Scholar
- Rutanen EM: Insulin-like growth factors and insulin-like growth factor binding proteins in the endometrium. Effect of intrauterine levonorgestrel delivery. Hum Reprod. 2000, 15 (Suppl 3): 173-181.View ArticlePubMedGoogle Scholar
- Shiozawa T, Nikaido T, Nakayama K, Lu X, Fujii S: Involvement of cyclin-dependent kinase inhibitor p27Kip1 in growth inhibition of endometrium in the secretory phase and of hyperplastic endometrium treated with progesterone. Mol Hum Reprod. 1998, 4: 899-905. 10.1093/molehr/4.9.899.View ArticlePubMedGoogle Scholar
- Jackman M, Lindon C, Nigg EA, Pines J: Active cyclin B1-Cdk1 first appears on centrosomes in prophase. Nat Cell Biol. 2003, 5: 143-148. 10.1038/ncb918.View ArticlePubMedGoogle Scholar
- Jin P, Hardy S, Morgan DO: Nuclear localization of cyclin B1 controls mitotic entry after DNA damage. J Cell Biol. 1998, 141: 875-885. 10.1083/jcb.141.4.875.PubMed CentralView ArticlePubMedGoogle Scholar
- Grabsch H, Lickvers K, Hansen O, Takeno S, Willers R, Stock W, Gabbert HE, Mueller W: Prognostic value of cyclin B1 protein expression in colorectal cancer. Am J Clin Pathol. 2004, 122: 511-516. 10.1309/54H4Q88A1UBBWPTE.View ArticlePubMedGoogle Scholar
- Shiozawa T, Li SF, Nakayama K, Nikaido T, Fujii S: Relationship between the expression of cyclins/cyclin-dependent kinases and sex-steroid receptors/Ki67 in normal human endometrial glands and stroma during the menstrual cycle. Mol Hum Reprod. 1996, 2: 745-752. 10.1093/molehr/2.10.745.View ArticlePubMedGoogle Scholar
- Milde-Langosch K, Bamberger AM, Goemann C, Rossing E, Rieck G, Kelp B, Loning T: Expression of cell-cycle regulatory proteins in endometrial carcinomas: correlations with hormone receptor status and clinicopathologic parameters. J Cancer Res Clin Oncol. 2001, 127: 537-544. 10.1007/s004320100256.View ArticlePubMedGoogle Scholar
- Tong W, Pollard JW: Progesterone inhibits estrogen-induced cyclin D1 and cdk4 nuclear translocation, cyclin E- and cyclin A-cdk2 kinase activation, and cell proliferation in uterine epithelial cells in mice. Mol Cell Biol. 1999, 19: 2251-2264.PubMed CentralView ArticlePubMedGoogle Scholar
- Korgun ET, Celik-Ozenci C, Acar N, Cayli S, Desoye G, Demir R: Location of cell cycle regulators cyclin B1, cyclin A, PCNA, Ki67 and cell cycle inhibitors p21, p27 and p57 in human first trimester placenta and deciduas. Histochem Cell Biol. 2006, 125: 615-624. 10.1007/s00418-006-0160-y.View ArticlePubMedGoogle Scholar
- Lee WS, Liu CW, Juan SH, Liang YC, Ho PY, Lee YH: Molecular mechanism of progesterone-induced antiproliferation in rat aortic smooth muscle cells. Endocrinology. 2003, 144: 2785-2790. 10.1210/en.2003-0045.View ArticlePubMedGoogle Scholar
- Tang L, Wang TT, Wu YT, Zhou CY, Huang HF: High expression levels of cyclin B1 and Polo-like kinase 1 in ectopic endometrial cells associated with abnormal cell cycle regulation of endometriosis. Fertil Steril. 2009, 91: 979-987. 10.1016/j.fertnstert.2008.01.041.View ArticlePubMedGoogle Scholar
- Tsuda H, Hashiguchi Y, Inoue T, Yamamoto K: Alteration of G2 cell cycle regulators occurs during carcinogenesis of the endometrium. Oncology. 2003, 65: 159-166. 10.1159/000072342.View ArticlePubMedGoogle Scholar
- Rudolph P, Kuhling H, Alm P, Ferno M, Baldetorp B, Olsson H, Parwaresch R: Differential prognostic impact of the cyclins E and B in premenopausal and postmenopausal women with lymph node-negative breast cancer. Int J Cancer. 2003, 105: 674-680. 10.1002/ijc.11132.View ArticlePubMedGoogle Scholar
- Chen B, Pan H, Zhu L, Deng Y, Pollard JW: Progesterone inhibits the estrogen-induced phosphoinositide 3-kinase-->AKT-->GSK-3beta-->cyclin D1-->pRB pathway to block uterine epithelial cell proliferation. Mol Endocrinol. 2005, 19: 1978-1990. 10.1210/me.2004-0274.View ArticlePubMedGoogle Scholar
- Ohta K, Maruyama T, Uchida H, Ono M, Nagashima T, Arase T, Kajitani T, Oda H, Morita M, Yoshimura Y: Glycodelin blocks progression to S phase and inhibits cell growth: a possible progesterone-induced regulator for endometrial epithelial cell growth. Mol Hum Reprod. 2008, 14: 17-22. 10.1093/molehr/gam081.View ArticlePubMedGoogle Scholar
- Paulssen RH, Moe B, Gronaas H, Orbo A: Gene expression in endometrial cancer cells (Ishikawa) after short time high dose exposure to progesterone. Steroids. 2008, 73: 116-128. 10.1016/j.steroids.2007.09.010.View ArticlePubMedGoogle Scholar
- Matsumoto Y, Iwasaka T, Yamasaki F, Sugimori H: Apoptosis and Ki-67 expression in adenomyotic lesions and in the corresponding eutopic endometrium. Obstet Gynecol. 1999, 94: 71-77. 10.1016/S0029-7844(99)00279-3.View ArticlePubMedGoogle Scholar
- Soni DV, Jacobberger JW: Inhibition of cdk1 by alsterpaullone and thioflavopiridol correlates with increased transit time from mid G2 through prophase. Cell Cycle. 2004, 3: 349-357.View ArticlePubMedGoogle Scholar
- Lahusen T, De Siervi A, Kunick C, Senderowicz AM: Alsterpaullone, a novel cyclin-dependent kinase inhibitor, induces apoptosis by activation of caspase-9 due to perturbation in mitochondrial membrane potential. Mol Carcinog. 2003, 36: 183-194. 10.1002/mc.10114.View ArticlePubMedGoogle Scholar
- Borgne A, Versteege I, Mahe M, Studeny A, Leonce S, Naime I, Rodriguez M, Hickman JA, Meijer L, Golsteyn RM: Analysis of cyclin B1 and CDK activity during apoptosis induced by camptothecin treatment. Oncogene. 2006, 25: 7361-7372. 10.1038/sj.onc.1209718.View ArticlePubMedGoogle Scholar
- Shapiro GI: Preclinical and clinical development of the cyclin-dependent kinase inhibitor flavopiridol. Clin Cancer Res. 2004, 10: 4270s-4275s. 10.1158/1078-0432.CCR-040020.View ArticlePubMedGoogle Scholar
- Schultz C, Link A, Leost M, Zaharevitz DW, Gussio R, Sausville EA, Meijer L, Kunick C: Paullones, a series of cyclin-dependent kinase inhibitors: synthesis, evaluation of CDK1/cyclin B inhibition, and in vitro antitumor activity. J Med Chem. 1999, 42: 2909-2919. 10.1021/jm9900570.View ArticlePubMedGoogle Scholar
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