Modulation of pp60v-src and pp60c-src expression in Rous sarcoma virus-transformed hamster fibroblasts transfected with activated N-ras.
Three phenotypically different hamster cell lines transformed with Rous sarcoma virus (RSV) were transfected with plasmid DNA containing an activated N-ras oncogene, and nine clones expressing various levels of p21N-ras were characterized. We examined the effects of p21N-ras on expression and kinase activity of resident src proteins by using a variety of assays that allowed us to discriminate between viral and cellular src proteins. In eight clones with a 10- to 20-fold increase in p21N-ras levels relative to the endogenous protein, we observed a marked reduction in the synthesis and kinase activity of p60v-src. This decrease correlated with transcriptional downregulation of RSV genomic and v-src subgenomic mRNAs. In the same cells, we found a concomitant accumulation of p60c-src and, accordingly, an increase in its protein kinase activity without an apparent increase in c-src mRNA levels. Therefore, modulation of viral and cellular src proteins in cells overexpressing p21N-ras appeared to result from two distinct effects: a downregulation of long terminal repeat-driven transcription and a more complex interaction with cellular effectors that control the stability of p60c-src. Such modulation also seemed to depend on the levels of p21N-ras and, possibly, on host-cell factors, since it was not observed in the third cell line, in which the relative increase in p21N-ras was only 2.5-fold to fivefold.
Topol
L Z
LZ
Laboratory of Molecular Oncology, National Cancer Institute, Frederick, Maryland 21702-1201.
Kisseljova
N P
NP
Gutierrez
M L
ML
Deichman
G I
GI
Musatkina
E A
EA
Shtutman
M S
MS
Zakamaldina
T Z
TZ
Blair
D G
DG
Tatosyan
A G
AG
D000818:Animals; D001358:Avian Sarcoma Viruses; D002472:Cell Transformation, Viral; D002478:Cells, Cultured; D006224:Cricetinae; D005786:Gene Expression Regulation; D011905:Genes, ras; D015151:Immunoblotting; D015688:Oncogene Protein pp60(v-src) / Q000378:metabolism*; D014162:Transfection
D015688:Oncogene Protein pp60(v-src)