v-Ras and v-Raf block differentiation of transformable C3H10T1/2-derived preadipocytes at lower levels than required for neoplastic transformation.
To investigate the functional relationship between the transforming ability of Ras and its role as an integral component of the differentiative insulin signaling pathway, we introduced a leu61-activated ras gene into a Ras-transformable, C3H10T1/2-derived preadipocytic cell line. The results demonstrate that rasleu61 expression in this line blocks differentiation and that this block appears at lower levels than required for full neoplastic transformation. In addition, to examine whether the inability of Rasleu61 to induce differentiation by replacing the insulin signal could be attributed to its transforming effect in this system, we examined the effect of Rasleu61 at levels below the baseline, by expressing rasleu61 in a series of preadipocytes which were rendered deficient in endogenous c-Ras activity. The results show that even very low Rasleu61 levels, insufficient to restore the growth rate of these cells to normal, blocked rather than enhanced differentiation, indicating that rasleu61 expression alone is not sufficient to promote adipocytic differentiation in this system, even in the absence of neoplastic transformation. Consistent with its established role as a downstream effector of Ras, v-Raf expression mirrored the v-Ras effects upon adipocytic differentiation and transformation.
Raptis
L
L
Department of Microbiology and Immunology, Queen's University, Kingston, Ontario, Canada. RaptisL@Post.QueensU.ca
Brownell
H L
HL
Lu
Y
Y
Preston
T
T
Narsimhan
R P
RP
Anderson
S
S
Schaefer
E
E
Haliotis
T
T
D017667:Adipocytes / Q000166:cytology* / Q000378:metabolism; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002454:Cell Differentiation; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D004789:Enzyme Activation; D011905:Genes, ras; D007700:Kinetics; D051379:Mice; D008809:Mice, Inbred C3H; D015689:Oncogene Protein p21(ras) / Q000096:biosynthesis*; D027384:Oncogene Proteins v-raf; D009857:Oncogenes; D011505:Protein-Tyrosine Kinases / Q000096:biosynthesis; D011994:Recombinant Proteins / Q000096:biosynthesis; D015682:Retroviridae Proteins, Oncogenic / Q000096:biosynthesis*; D014162:Transfection
D011994:Recombinant Proteins; D015682:Retroviridae Proteins, Oncogenic; D011505:Protein-Tyrosine Kinases; D027384:Oncogene Proteins v-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D015689:Oncogene Protein p21(ras)