Progesterone receptors induce cell cycle progression via activation of mitogen-activated protein kinases.
Progestins induce proliferation of breast cancer cells and are implicated in the development of breast cancer. The effects of progestins are mediated by progesterone receptors (PRs), although it is unclear whether proliferative effects are delivered through activities as ligand-activated transcription factors or via activation of cytoplasmic kinases. We report that progestin induces S phase entry of T47D cells stably expressing either wild-type (wt) PR-B or a transcriptionally impaired PR-B harboring a point mutation at Ser294, a ligand-dependent and MAPK consensus phosphorylation site (S294A). Both wt and S294A PR are capable of activating p42/p44 MAPKs and promoting proliferation. However, cells expressing wt, but not S294A PR, exhibited enhanced proliferation in response to combined epidermal growth factor and progestin. S phase progression correlated with up-regulation of cyclin D1. The PR antagonist RU486 also induced MAPK activation, increased cyclin D1 expression, and stimulated S phase entry, which was blocked by inhibition of either p42/p44 or p38 MAPKs, whereas proliferation induced by R5020 was sensitive only to p42/p44 MAPK inhibition. MCF-7 cells stably expressing a mutant PR unable to bind c-Src and activate MAPK failed to support progestin-induced proliferation. These data suggest that PR mediate cell cycle progression primarily through activation of cytoplasmic kinases and independently of direct regulation of transcription, whereas the coordinate regulation of both aspects of PR action are required for enhanced proliferation in response to progestins in the presence of growth factors. Targeting the ability of steroid receptors to activate MAPKs may be beneficial for breast cancer patients.
Department of Medicine, Division of Hematology, Oncology, and Transplantation, University of Minnesota Cancer Center, MMC 806, 420 Delaware Street SE, Minneapolis, Minnesota 55455, USA.
Andrew
A
Skildum
Emily
E
Faivre
Carol A
CA
Lange
D001665:Binding Sites; D015153:Blotting, Western; D002453:Cell Cycle; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D019938:Cyclin D1 / Q000378:metabolism; D018450:Disease Progression; D015536:Down-Regulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000378:metabolism; D066246:ErbB Receptors / Q000378:metabolism; D006801:Humans; D008024:Ligands; D008156:Luciferases / Q000378:metabolism; D020935:MAP Kinase Signaling System; D015735:Mifepristone / Q000494:pharmacology; D010766:Phosphorylation; D017354:Point Mutation; D011372:Progestins / Q000378:metabolism; D011980:Receptors, Progesterone / Q000378:metabolism*; D016196:S Phase; D012694:Serine / Q000737:chemistry; D013997:Time Factors; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D015854:Up-Regulation
D016895:Culture Media, Serum-Free; D004791:Enzyme Inhibitors; D008024:Ligands; D011372:Progestins; D011980:Receptors, Progesterone; D019938:Cyclin D1; D015735:Mifepristone; D012694:Serine; D004815:Epidermal Growth Factor; D008156:Luciferases; D066246:ErbB Receptors