Effects of increased expression of protein kinase C on radiation-induced cell transformation.
The in vitro oncogenic transformation of C3H 10T1/2 cells by ionizing radiation is known to be enhanced by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). It is also known that the activation of protein kinase C (PKC) by TPA is an important step in its tumor-promoting effect. In the present study, we examined the effects of overexpression of a specific isoform of PKC, PKC beta 1 on gamma-ray-induced transformation of 10T1/2 cells. In addition, the effects of overexpression of PKC beta 1 on the malignant phenotype of a previously transformed 10T1/2 cell line were also evaluated. Derivatives of 10T1/2 cells that stably overexpress PKC beta 1 were obtained by transduction with the retroviral expression vector pMV7 carrying the rat PKC beta 1 cDNA sequence. We found that the parental 10T1/2 cells and a control cell line 10T1/2 MV7, which carried only the pMV7 vector without the cDNA insert, expressed dose-dependent transformation frequencies when exposed to gamma-rays. On the other hand, concurrently treated PKC-overexpressing cells that had an 11-fold increase in enzyme activity (PKC-4 cells) failed to yield any morphologically identifiable foci. Cell lines that expressed lower levels of PKC beta 1 were partially resistant to transformation by gamma-rays. Clonogenic survival data indicated that this observation was not due to radioresistance per se. Thus, overexpression of PKC beta 1 did not appear to function as an endogenous substitute for TPA in promoting radiation-induced transformation. Furthermore, overexpression of PKC did not reverse the transformation phenotypes in tumorigenic 10T1/2 cells once it was established. These findings are discussed with respect to the specific roles of individual isoforms of PKC in growth control.
Hei
T K
TK
Center for Radiological Research, College of Physicians & Surgeons, New York, NY.
Krauss
R S
RS
Liu
S X
SX
Hall
E J
EJ
Weinstein
I B
IB
D000818:Animals; D002455:Cell Division; D002471:Cell Transformation, Neoplastic / Q000528:radiation effects*; D018076:DNA, Complementary; D005720:Gamma Rays; D051379:Mice; D008809:Mice, Inbred C3H; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism*; D011836:Radiation Tolerance; D051381:Rats
D018076:DNA, Complementary; D011493:Protein Kinase C