Transformation by v-src causes transient induction followed by repression of mouse thrombospondin-1.
Thrombospondin-1 (TSP-1) is an extracellular glycoprotein that plays a role in neoplasia, cell growth, and differentiation. We have examined the regulation of TSP-1 mRNA in cells expressing the v-src oncogene. Rat1 fibroblasts constitutively transformed by v-src expressed TSP-1 mRNA at levels that were 10- to 50-fold lower than those observed in parental, vector-transfected control cells. To analyze the kinetics of this effect, we used a line of BALB/c 3T3 fibroblasts containing a thermolabile v-src gene. Prolonged culture of these cells at the permissive temperature also resulted in down-regulation of TSP-1 mRNA. However, at early time points after temperature shift of growth-arrested cells, we observed a 3- to 15-fold increase in TSP-1 mRNA. This induction was abolished by the tyrosine kinase inhibitor, herbimycin-A, but not by the protein synthesis inhibitor, cycloheximide. The induction of TSP-1 by v-src occurred at a transcriptional level, as determined by nuclear run-on assays. Furthermore, the effect was mediated in part by a short region of the TSP-1 promoter which contains only 41 base pairs of 5' flanking DNA and 48 base pairs of the first exon. We conclude that, while overexpression of v-src results in brief transcriptional induction of TSP-1, the ultimate result of v-src transformation, at least in rodent fibroblasts, is repression of TSP-1 gene expression.
Slack
J L
JL
Department of Biochemistry, University of Washington, Seattle 98195.
Bornstein
P
P
D000818:Animals; D015815:Cell Adhesion Molecules / Q000096:biosynthesis; D002460:Cell Line; D002461:Cell Line, Transformed; D002467:Cell Nucleus / Q000378:metabolism; D002471:Cell Transformation, Neoplastic; D015500:Chloramphenicol O-Acetyltransferase / Q000096:biosynthesis; D015870:Gene Expression; D016391:Genes, src; D008562:Membrane Glycoproteins / Q000096:biosynthesis*; D008668:Metallothionein / Q000235:genetics; D051379:Mice; D010957:Plasmids; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D019699:Thrombospondins; D014162:Transfection
D015815:Cell Adhesion Molecules; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D019699:Thrombospondins; D008668:Metallothionein; D015500:Chloramphenicol O-Acetyltransferase