Oncogenic Ki-ras confers a more aggressive colon cancer phenotype through modification of transforming growth factor-beta receptor III.
Transforming growth factor-beta1 (TGF-beta1) can act as a tumor suppressor or a tumor promoter depending on the characteristics of the malignant cell. Each of three Ki-ras(G12V) transfectants of HD6-4 colon cancer cells had been shown to be more aggressive in vivo than controls in earlier studies (Yan, Z., Chen, M., Perucho, M., and Friedman, E. (1997) J. Biol. Chem. 272, 30928-30936). We now show that stable expression of oncogenic Ki-ras(G12V) converts the HD6-4 colon cancer cell line from insensitive to TGF-beta1 to growth-promoted by TGF-beta1. Each of three Ki-ras(G12V) transfectants responded to TGF-beta1 by an increase in proliferation and by decreasing the abundance of the Cdk inhibitor p21 and the tumor suppressor PTEN, whereas each of three wild-type Ki-ras transfectants remained unresponsive to TGF-beta1. The wild-type Ki-ras transfectants lack functional TGF-beta receptors, whereas all three Ki-ras(G12V) transfectants expressed functional TGF-beta receptors that bound (125)I-TGF-beta1. The previous studies showed that in cells with wild-type Ki-ras, TGF-beta receptors were not mutated, and receptor proteins were transported to the cell surface, but post-translational modification of TGF-beta receptor III (TbetaRIII) was incomplete. We now show that the betaglycan form of TbetaRIII is highly modified following translation when transiently expressed in Ki-ras(G12V) cells, whereas no such post-translational modification of TbetaRIII occurs in control cells. Antisense oligonucleotides directed to Ki-Ras decreased both TbetaRIII post-translational modification in Ki-ras(G12V) cells and TGF-beta1 down-regulation of p21, demonstrating the direct effect of mutant Ras. Therefore, one mechanism by which mutant Ki-Ras confers a more aggressive tumor phenotype is by enhancing TbetaRIII post-translational modification.
Yan
Z
Z
Department of Pathology, Upstate Medical University, State University of New York, Syracuse, New York 13210, USA.
Deng
X
X
Friedman
E
E
D030201:Activin Receptors, Type I; D000818:Animals; D002455:Cell Division; D003110:Colonic Neoplasms / Q000235:genetics* / Q000473:pathology*; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D004791:Enzyme Inhibitors; D011905:Genes, ras; D006801:Humans; D009361:Neoplasm Invasiveness; D010641:Phenotype; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D011509:Proteoglycans / Q000235:genetics* / Q000378:metabolism*; D051381:Rats; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics* / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D014407:Tumor Cells, Cultured
C493956:CDKN1A protein, human; C493958:Cdkn1a protein, rat; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D011509:Proteoglycans; D018125:Receptors, Transforming Growth Factor beta; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; C071736:betaglycan; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I; C000625843:Tgfbr1 protein, rat