title: Role of tyrosine kinase Jak2 in prolactin-induced differentiation and growth of mammary epithelial cells.
abstract: Genetic studies in mice have established a critical role for prolactin receptors and transcription factor Stat5 in mammary gland differentiation. However, the enzymatic coupling between prolactin receptors and Stat5 in this process has not been established. In addition to Jak2, several other tyrosine kinases reportedly also are associated with prolactin receptors and may phosphorylate Stat5. Because Jak2 null mice die in utero, we targeted Jak2 in an ex vivo model of prolactin-induced mammary epithelial cell differentiation to determine the role of Jak2 in regulation of cell differentiation and growth. Two independent targeting strategies were used to suppress Jak2 in immortalized HC11 mouse mammary epithelial cells: 1) stable expression of a specific Jak2 antisense construct and 2) adenoviral delivery of a dominant-negative Jak2 gene. We now demonstrate that Jak2 is essential for prolactin-induced differentiation and activation of Stat5 in normal mouse mammary epithelial cells. Furthermore, suppression of Jak2 in HC11 cells was associated with constitutive activation of oncoprotein Stat3 and a hyperproliferative phenotype characterized by increased mitotic rate, reduced apoptosis, and reduced contact inhibition. Collectively, our data suggest that Jak2 is differentiation-inducing and growth-inhibitory in normal mammary epithelial cells, observations that may shed new light on the role of the Jak2-Stat5 pathway in breast cancer.
authors.affiliation: United States Military Cancer Institute and Department of Pathology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814, USA.
authors.forename: Jianwu
authors.initials: J
authors.lastname: Xie
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: LeBaron
authors.forename: Marja T
authors.initials: MT
authors.lastname: Nevalainen
authors.forename: Hallgeir
authors.initials: H
authors.lastname: Rui
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D017209:Apoptosis; D001943:Breast Neoplasms / Q000378:metabolism; D019556:COS Cells; D002454:Cell Differentiation; D002455:Cell Division; D002460:Cell Line; D002470:Cell Survival; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells / Q000378:metabolism*; D005434:Flow Cytometry; D005799:Genes, Dominant; D015151:Immunoblotting; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D053614:Janus Kinase 2; D008321:Mammary Glands, Animal / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D008894:Milk Proteins; D008938:Mitosis; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D010641:Phenotype; D016133:Polymerase Chain Reaction; D011233:Precipitin Tests; D011388:Prolactin / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D011518:Proto-Oncogene Proteins; D050796:STAT3 Transcription Factor; D050799:STAT5 Transcription Factor; D012756:Sheep; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism; D014162:Transfection
chemical_list: D004268:DNA-Binding Proteins; D008894:Milk Proteins; D016376:Oligonucleotides, Antisense; D011518:Proto-Oncogene Proteins; D050796:STAT3 Transcription Factor; D050799:STAT5 Transcription Factor; C494087:Stat3 protein, mouse; D015534:Trans-Activators; D011388:Prolactin; D011505:Protein-Tyrosine Kinases; C507926:Jak2 protein, mouse; D053614:Janus Kinase 2