title: Role of c-Myb during prolactin-induced signal transducer and activator of transcription 5a signaling in breast cancer cells.
abstract: Implicated in the pathogenesis of breast cancer, prolactin (PRL) mediates its function in part through the prolactin receptor (PRLr)-associated Janus kinase 2 (Jak2)/signal transducer and activator of transcription 5 (Stat5) signaling complex. To delineate the mechanisms of Stat5a regulation in breast cancer, transcription factor-transcription factor (TF-TF) array analysis was employed to identify associated transcriptional regulators. These analyses revealed a PRL-inducible association of Stat5a with the transcription factor and protooncogene c-Myb. Confirmatory co-immunoprecipitation studies using lysates from both T47D and MCF7 breast cancer cells revealed a PRL-inducible association between these transcription factors. Ectopic expression of c-Myb enhanced the PRL-induced expression from both composite and synthetic Stat5a-responsive luciferase reporters. Chromatin immunoprecipitation assays also revealed a PRL-inducible association between c-Myb and endogenous Stat5a-responsive CISH promoter, which was associated with an enhanced expression of CISH gene product at the RNA and protein levels. Small interfering RNA-mediated c-Myb knockdown impaired the PRL-induced mRNA expression of five Stat5-responsive genes. DNA binding-defective mutants of c-Myb, incapable of activating expression from a c-Myb-responsive reporter, maintained their ability to enhance a Stat5a-responsive reporter. At a cellular level, ectopic expression of c-Myb resulted in an increase in T47D proliferation. Taken together, these results indicate that c-Myb potentiates Stat5a-driven gene expression, possibly functioning as a Stat5a coactivator, in human breast cancer.
authors.affiliation: Department of Pathology, Robert H. Lurie Comprehensive Cancer Center, Northwestern University, Chicago, Illinois 60611, USA.
authors.forename: Feng
authors.initials: F
authors.lastname: Fang
authors.forename: Michael A
authors.initials: MA
authors.lastname: Rycyzyn
authors.forename: Charles V
authors.initials: CV
authors.lastname: Clevenger
mesh_terms: D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D047369:Chromatin Immunoprecipitation; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D047468:Immunoprecipitation; D011388:Prolactin / Q000494:pharmacology*; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding / Q000187:drug effects; D020598:Proto-Oncogene Proteins c-myb / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D034741:RNA, Small Interfering / Q000235:genetics / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050799:STAT5 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D050826:Suppressor of Cytokine Signaling Proteins / Q000235:genetics / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D011388:Prolactin; D020598:Proto-Oncogene Proteins c-myb; D034741:RNA, Small Interfering; D050799:STAT5 Transcription Factor; D050826:Suppressor of Cytokine Signaling Proteins; D025521:Tumor Suppressor Proteins; C494092:STAT5A protein, human