title: SOCS3 as a tumor suppressor in breast cancer cells, and its regulation by PRL.
abstract: Suppressor of cytokine signaling 3 (SOCS3), as a key regulator of cytokine signaling, has the potential to modulate numerous cellular processes. Its involvement in inflammatory disease is well established, and there is increasing evidence for a role in breast cancer as a regulator of signal transducers and activators of transcription (STATs). Here we show that over-expression of SOCS3 markedly supresses STAT3 expression, and abrogates STAT5 phosphorylation, resulting in decreased cell proliferation in T47D breast cancer cells, and decreased proliferation and anchorage-independent growth in MCF7 cells. Using T47D cells, we elucidated the signaling pathways and transcription factors involved in SOCS3 expression in response to prolactin, a key mammotropic hormone. Quantitative real time PCR was used to examine SOCS3 mRNA expression, IP/WB was used to examine STAT phosphorylation, luciferase reporter assays, chromatin immunoprecipitation (ChIP) and gel shift assays allowed evaluation of cis-elements and trans-factors regulating SOCS3 expression. We demonstrate that prolactin-induced SOCS3 expression is STAT-dependant, predominantly involving STAT5, although STAT1 is also associated with the promoter. In addition, prolactin-induced SOCS3 promoter activation requires PKA-stimulated Sp1 binding to the GC-rich region of the promoter. Finally, we show that PRL-induced SOCS3 expression can be potentiated by co-treatment with PGE(2). This study demonstrates that SOCS3 acts as an anti-proliferative agent in breast cancer cells, and highlights the complexity of SOCS3 regulation and crosstalk.
authors.affiliation: The School of Biomedical Sciences, University of Queensland, Queensland, Australia. j.barclay@imb.uq.edu.au
authors.forename: Johanna L
authors.initials: JL
authors.lastname: Barclay
authors.forename: Stephen T
authors.initials: ST
authors.lastname: Anderson
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Waters
authors.forename: Jon D
authors.initials: JD
authors.lastname: Curlewis
mesh_terms: D001943:Breast Neoplasms / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D047369:Chromatin Immunoprecipitation; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008954:Models, Biological; D010766:Phosphorylation; D011388:Prolactin / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D050794:STAT1 Transcription Factor / Q000378:metabolism; D050799:STAT5 Transcription Factor / Q000378:metabolism; D016329:Sp1 Transcription Factor / Q000378:metabolism; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000378:metabolism / Q000502:physiology*
chemical_list: D012333:RNA, Messenger; C106644:SOCS3 protein, human; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050799:STAT5 Transcription Factor; D016329:Sp1 Transcription Factor; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D011388:Prolactin