Signaling pathways regulating TC21-induced tumorigenesis.
TC21(R-Ras2), a Ras-related GTPase with transforming potential similar to H-, K- and N-Ras, is implicated in the pathogenesis of human cancers. Transforming growth factor beta (TGF-beta), a cytokine that plays a significant role in modulating tumorigenesis, normally prevents uncontrolled cell proliferation but paradoxically induces proliferation in H-Ras-transformed cancer cells. Although TC21 activates some pathways that mediate cellular transformation by the classical Ras proteins, the mechanisms through which TC21 induces tumor formation and how TGF-beta regulates TC21 transformed cells is not known. To better understand the role of TC21 in cancer progression, we overexpressed an activated G23V mutant of TC21 in a nontumorigenic murine mammary epithelial (EpH4) cell line. Mutant TC21-expressing cells were significantly more oncogenic than cells expressing activated G12V H-Ras both in vivo and in vitro. TC21-induced transformation and proliferation required activation of p38 MAPK, mTOR (the mammalian target of rapamycin), and phosphoinositide 3-kinase but not Akt/PKB. Transformation by TC21 rendered EpH4 cells insensitive to the growth inhibitory effects of TGF-beta, and the soft agar growth of these cells was increased upon TGF-beta stimulation. Despite losing responsiveness to TGF-beta-mediated growth inhibition, both Smad-dependent and independent pathways remained intact in TC21-transformed cells. Thus, overexpression of active TC21 in EpH4 cells induces tumorigenicity through the phosphoinositide 3-kinase, p38 MAPK, and mTOR pathways, and these cells lose their sensitivity to the normal growth inhibitory role of TGF-beta.
Erdogan
Mete
M
Department of Cancer Biology, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA.
Pozzi
Ambra
A
Bhowmick
Neil
N
Moses
Harold L
HL
Zent
Roy
R
D000818:Animals; D045744:Cell Line, Tumor; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D020935:MAP Kinase Signaling System; D008565:Membrane Proteins / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D020559:Monomeric GTP-Binding Proteins / Q000502:physiology*; D011494:Protein Kinases / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases; D016212:Transforming Growth Factor beta / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism
D008565:Membrane Proteins; D016212:Transforming Growth Factor beta; D011494:Protein Kinases; C546842:MTOR protein, human; C546843:mTOR protein, mouse; D058570:TOR Serine-Threonine Kinases; D048051:p38 Mitogen-Activated Protein Kinases; C087360:RRAS2 protein, human; C490200:Rras2 protein, mouse; D020559:Monomeric GTP-Binding Proteins; D018631:ras Proteins