Signaling through Ras is essential for ret oncogene-induced cell differentiation in PC12 cells.
Specific germline mutations of the receptor tyrosine kinase, Ret, predispose to multiple endocrine neoplasia types 2A and 2B and familial medullary thyroid carcinoma. The mechanisms by which different Ret isoforms (Ret-2A and Ret-2B) cause distinct neoplastic diseases remain largely unknown. On the other hand, forced expression of these mutated versions of Ret induces the rat pheochromocytoma cell line, PC12, to differentiate. Here we used an inducible vector encoding a dominant-negative Ras (Ras p21(N17)) to investigate the contributions of the Ras pathway to the phenotype induced in PC12 cells by the expression of either Ret-2A or Ret-2B mutants. We show that the Ret-induced molecular and morphological changes are both mediated by Ras-dependent pathways. However, even though inhibition of Ras activity was sufficient to revert Ret-induced differentiation, the kinetics of morphological reversion of the Ret-2B- was more rapid than the Ret-2A-transfected cells. Further, we show that in Ret-transfected cells the suc1-associated neurotrophic factor-induced tyrosine phosphorylation target, SNT, is chronically phosphorylated in tyrosine residues, and associates with the Sos substrate. These results indicate the activation of the Ras cascade as an essential pathway triggered by the chronic active Ret mutants in PC12 cells. Moreover, our data indicate SNT as a substrate for both Ret mutants, which might mediate the activation of this cascade.
Califano
D
D
Centro di Endocrinologia ed Oncologia Sperimentale del Consiglio Nazionale delle Ricerche, c/o Dipartimento di Biologia e Patologia Cellulare e Molecolare, Università di Napoli "Federico II," via S. Pansini 5, 80131 Naples, Italy.
Rizzo
C
C
D'Alessio
A
A
Colucci-D'Amato
G L
GL
Cali
G
G
Bartoli
P C
PC
Santelli
G
G
Vecchio
G
G
de Franciscis
V
V
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002454:Cell Differentiation / Q000235:genetics*; D029721:Drosophila Proteins; D008565:Membrane Proteins / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D015689:Oncogene Protein p21(ras) / Q000378:metabolism*; D009857:Oncogenes; D016716:PC12 Cells; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D051096:Proto-Oncogene Proteins c-ret; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics*; D015398:Signal Transduction; D014443:Tyrosine / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D029721:Drosophila Proteins; C106534:FRS2 protein, human; D008565:Membrane Proteins; D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; D014443:Tyrosine; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases; C416649:Ret protein, Drosophila; C495001:Ret protein, rat; D015689:Oncogene Protein p21(ras)