Essential functions of p21-activated kinase 1 in morphogenesis and differentiation of mammary glands.
Although growth factors have been shown to influence mammary gland development, the nature of downstream effectors remains elusive. In this study, we show that the expression of p21-activated kinase (Pak)1, a serine/threonine protein kinase, is activated in mammary glands during pregnancy and lactation. By targeting an ectopic expression of a kinase-dead Pak1 mutant under the control of ovine beta-lactoglobulin promoter, we found that the mammary glands of female mice expressing kinase-dead Pak1 transgene revealed incomplete lobuloalveolar development and impaired functional differentiation. The expression of whey acidic protein and beta-casein and the amount of activated Stat5 in the nuclei of epithelial cells in transgenic mice were drastically reduced. Further analysis of the underlying mechanisms revealed that Pak1 stimulated beta-casein promoter activity in normal mouse mammary epithelial cells and also cooperated with Stat5a. Pak1 directly interacted with and phosphorylated Stat5a at Ser 779, and both COOH-terminal deletion containing Ser 779 of Stat5a and the Ser 779 to Ala mutation completely prevented the ability of Pak1 to stimulate beta-casein promoter. Mammary glands expressing inactive Pak1 exhibited a reduction of Stat5a Ser 779 phosphorylation. These findings suggest that Pak1 is required for alveolar morphogenesis and lactation function, and thus, identify novel functions of Pak1 in the mammary gland development.
Department of Molecular and Cellular Oncology, The University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, USA.
Rui-An
RA
Wang
Ratna K
RK
Vadlamudi
Rozita
R
Bagheri-Yarmand
Iwan
I
Beuvink
Nancy E
NE
Hynes
Rakesh
R
Kumar
D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002364:Caseins / Q000378:metabolism; D002454:Cell Differentiation / Q000235:genetics; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism; D015536:Down-Regulation / Q000235:genetics; D004847:Epithelial Cells / Q000166:cytology / Q000201:enzymology*; D005260:Female; D007774:Lactation / Q000235:genetics; D008321:Mammary Glands, Animal / Q000166:cytology / Q000201:enzymology* / Q000254:growth & development*; D051379:Mice; D008822:Mice, Transgenic; D008894:Milk Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation; D011247:Pregnancy / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency* / Q000235:genetics; D050799:STAT5 Transcription Factor; D012694:Serine / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism; D019076:Transgenes / Q000235:genetics; D054462:p21-Activated Kinases
D002364:Caseins; D004268:DNA-Binding Proteins; D008894:Milk Proteins; D050799:STAT5 Transcription Factor; C494093:Stat5a protein, mouse; D015534:Trans-Activators; C024471:whey acidic proteins; D012694:Serine; C515905:Pak1 protein, mouse; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases