BRCA1-IRIS activates cyclin D1 expression in breast cancer cells by downregulating the JNK phosphatase DUSP3/VHR.
Cyclin D1 plays an important role in cell cycle progression. In breast cancer, Cyclin D1 expression is deregulated by several mechanisms. We previously showed that in breast cancer cells, overexpression of BRCA1-IRIS induces Cyclin D1 overexpression and increases cell proliferation. BRCA1-IRIS alone or in complex with steroid receptor co-activators was targeted to the cyclin D1 promoter pre-bound by the c-Jun/AP1 and activated its transcription, which could explain the co-overexpression of BRCA1-IRIS and Cyclin D1 in breast cancer cells coupled with their increased proliferation. We report here an alternate or a complementary pathway by which BRCA1-IRIS activates Cyclin D1 expression. BRCA1-IRIS overexpression decreases the expression of the dual specificity phosphatase, DUSP3/VHR, an endogenous inhibitor of several MAPKs, including c-Jun N-terminal kinase. Although, the mechanism by which BRCA1-IRIS overexpression accomplishes that is not yet known, it is sufficient to induce Cyclin D1 overexpression in a human mammary epithelial cell model. Cyclin D1 overexpression could be blocked by co-overexpression of VHR in those cells. Furthermore, in 2 breast cancer cell lines that overexpress both BRCA1-IRIS and Cyclin D1 (MCF-7 and SKBR3) depletion of BRCA1-IRIS by RNA interference attenuated the expression of Cyclin D1 by elevating the expression level of VHR. These data demonstrate a critical role for BRCA1-IRIS in human breast cancer cell-cycle control and suggest that deregulated expression of BRCA1-IRIS is likely to reduce dependence on normal physiological growth stimuli, thereby providing a growth advantage to tumor cells and a potential mechanism of resistance to endocrine therapy.
Hao
Lu
L
Department of Pharmacology and Experimental Therapeutics, Stritch School of Medicine and Cardinal Bernardin Cancer Center, Loyola University Chicago, Maywood, IL 60153, USA.
ElShamy
Wael M
WM
D019313:BRCA1 Protein / Q000235:genetics / Q000378:metabolism*; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002453:Cell Cycle; D002460:Cell Line; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation; D054640:Dual Specificity Phosphatase 3; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D066246:ErbB Receptors / Q000378:metabolism; D047628:Estrogen Receptor alpha / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism
D019313:BRCA1 Protein; D019938:Cyclin D1; D054640:Dual Specificity Phosphatase 3; D066246:ErbB Receptors; D047628:Estrogen Receptor alpha; D048031:JNK Mitogen-Activated Protein Kinases; D010749:Phosphoprotein Phosphatases; D017027:Protein Tyrosine Phosphatases; D034741:RNA, Small Interfering; D018719:Erb-b2 Receptor Tyrosine Kinases; C492913:BRCA1 protein, human; C517025:DUSP3 protein, human