Src activation is not necessary for transforming growth factor (TGF)-beta-mediated epithelial to mesenchymal transitions (EMT) in mammary epithelial cells. PP1 directly inhibits TGF-beta receptors I and II.
Epithelial to mesenchymal transitions (EMTs) are key events during embryonic development and cancer progression. It has been proposed that Src plays a major role in some EMT models, as shown by the overexpression of viral Src (v-Src) in epithelial cells. It is clear that Src family kinases can regulate the integrity of both adherens junctions and focal adhesions; however, their significance in EMT, especially in the physiological context, remains to be elucidated. Here we showed that Src is activated in transforming growth factor-beta1 (TGF-beta1)-mediated EMT in mammary epithelial cells and that the Src family kinase inhibitor, PP1, prevents EMT. However, neither a more specific Src family kinase inhibitor, SU6656, nor a dominant-negative Src inhibited TGF-beta1-mediated EMT, leading us to speculate that Src activation is not an essential component of TGF-beta1-mediated EMT. Unexpectedly, PP1 prevented Smad2/3 activation by TGF-beta1, whereas SU6656 did not. Most interestingly, an in vitro kinase assay showed that PP1 strongly inhibited the TGF-beta receptor type I, and to a lesser extent, the TGF-beta receptor type II. Taken together, our data indicated that PP1 interferes with TGF-beta1-mediated EMT not by inhibiting Src family kinases but by inhibiting the Smad pathway via a direct inhibition of TGF-beta receptor kinase activity.
Maeda
Masato
M
Department of Oral Biology, College of Dentistry, University of Nebraska Medical Center, Nebraska Medical Center, Omaha 68198-7696, USA.
Shintani
Yasushi
Y
Wheelock
Margaret J
MJ
Johnson
Keith R
KR
D030201:Activin Receptors, Type I / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000166:cytology* / Q000378:metabolism; D007211:Indoles / Q000494:pharmacology; D008321:Mammary Glands, Animal / Q000166:cytology*; D008648:Mesoderm / Q000166:cytology* / Q000378:metabolism; D051379:Mice; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases; D016315:Proto-Oncogene Proteins c-abl / Q000378:metabolism; D011720:Pyrazoles / Q000378:metabolism*; D011743:Pyrimidines / Q000378:metabolism*; D000077293:Receptor, Transforming Growth Factor-beta Type I; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D051785:Smad Proteins / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D053773:Transforming Growth Factor beta1; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
C108123:4-amino-5-(4-methylphenyl)-7-(tert-butyl)pyrazolo(3,4-d)pyrimidine; D007211:Indoles; D047428:Protein Kinase Inhibitors; D011720:Pyrazoles; D011743:Pyrimidines; D018125:Receptors, Transforming Growth Factor beta; C416927:SU 6656; D051785:Smad Proteins; D013449:Sulfonamides; C508961:Tgfb1 protein, mouse; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D016315:Proto-Oncogene Proteins c-abl; D019061:src-Family Kinases; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I; D000077294:Receptor, Transforming Growth Factor-beta Type II