The role of p70S6K in hepatic stellate cell collagen gene expression and cell proliferation.
During fibrosis the hepatic stellate cell (HSC) undergoes a complex activation process characterized by increased proliferation and extracellular matrix deposition. The 70-kDa ribosomal S6 kinase (p70S6K) is activated by mitogens, growth factors, and hormones in a phosphatidylinositol 3-kinase-dependent manner. p70S6K regulates protein synthesis, proliferation, and cell cycle control. Because these processes are involved in HSC activation, we investigated the role of p70S6K in HSC proliferation, cell cycle control, and type I collagen expression. Platelet-derived growth factor (PDGF) stimulated p70S6K phosphorylation, which was blocked by LY294002, an inhibitor of phosphatidylinositol 3-kinase. Rapamycin blocked phosphorylation of p70S6K but had no affect on PDGF-induced Akt phosphorylation, positioning p70S6K downstream of Akt. Transforming growth factor-beta, which inhibits HSC proliferation, did not affect PDGF-induced p70S6K phosphorylation. Rapamycin treatment did not affect alpha1(I) collagen mRNA but reduced type I collagen protein secretion. Expression of smooth muscle alpha-actin was not affected by rapamycin treatment, indicating that HSC activation was not altered. Rapamycin inhibited serum-induced DNA synthesis approximately 2-fold. Moreover, rapamycin decreased expression of cyclins D1, D3, and E but not cyclin D2, Rb-Ser780, and Rb-Ser795. Together, p70S6K plays a crucial role in HSC proliferation, collagen expression, and cell cycle control, thus representing a potential therapeutic target for liver fibrosis.
Gäbele
Erwin
E
Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7032, USA.
Reif
Shimon
S
Tsukada
Shigeki
S
Bataller
Ramon
R
Yata
Yutaka
Y
Morris
Terry
T
Schrum
Laura W
LW
Brenner
David A
DA
Rippe
Richard A
RA
D000818:Animals; D002453:Cell Cycle / Q000502:physiology; D049109:Cell Proliferation; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D024042:Collagen Type I / Q000235:genetics* / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005355:Fibrosis / Q000378:metabolism; D005786:Gene Expression Regulation; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D008099:Liver / Q000378:metabolism / Q000473:pathology; D008297:Male; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017207:Rats, Sprague-Dawley; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D020123:Sirolimus / Q000494:pharmacology; D016212:Transforming Growth Factor beta / Q000378:metabolism
D002867:Chromones; D024042:Collagen Type I; D016213:Cyclins; D004247:DNA; D004791:Enzyme Inhibitors; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010982:Platelet-Derived Growth Factor; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D020123:Sirolimus; D016212:Transforming Growth Factor beta; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C494918:AKT1 protein, human; C494920:Akt1 protein, rat