Tropomyosin-2 cDNA lacking the 3' untranslated region riboregulator induces growth inhibition of v-Ki-ras-transformed fibroblasts.
The levels of high molecular weight isoforms of tropomyosin (TM) are markedly reduced in ras-transformed cells. Previous studies have demonstrated that the forced expression of tropomyosin-1 (TM-1) induces reversion of the transformed phenotype of ras-transformed fibroblasts. The effects of the related isoform TM-2 on transformation are less clear. To assess the effects of forced expression of the TM-2 protein on ras-induced tumorigenicity, we introduced a TM-2 cDNA lacking the 3' untranslated region riboregulator into ras-transformed NIH 3T3 fibroblasts. TM-2 expression resulted in a flatter cell morphology and restoration of stress fibers. TM-2 expression also significantly reduced growth rates in low serum, soft agar, and nude mice. The reduced growth rates were associated with a prolongation of G0-G1. To identify the mechanism of TM-2-induced growth inhibition, we analyzed the effects of TM-2 reexpression of ERK and c-jun N-terminal kinase (JNK) activities. Levels of ERK phosphorylation and activity in TM-2-transfected tumor cells were comparable to those in mock-transfected tumor cells. JNK activity was only modestly increased in ras-transformed cells relative to untransformed NIH 3T3 cells and only slightly reduced as result of forced TM-2 expression. We conclude that the partially restored expression of the TM-2 protein induces growth inhibition of ras-transformed NIH 3T3 cells without influencing ERK or JNK activities. Furthermore, the 3' untranslated region riboregulator of the alpha-tropomyosin gene is not needed for the inhibition of ras-induced growth.
Janssen
R A
RA
Division of Hematology/Oncology, New England Medical Center, Boston, Massachusetts 02111, USA.
Mier
J W
JW
D016475:3T3 Cells; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002455:Cell Division / Q000235:genetics / Q000502:physiology; D002461:Cell Line, Transformed; D002471:Cell Transformation, Neoplastic; D018076:DNA, Complementary; D005786:Gene Expression Regulation; D011905:Genes, ras; D007438:Introns; D048031:JNK Mitogen-Activated Protein Kinases; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D010641:Phenotype; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D014335:Tropomyosin / Q000235:genetics* / Q000502:physiology
D018076:DNA, Complementary; D014335:Tropomyosin; D011505:Protein-Tyrosine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases