Protein kinase C (PKC) promotes cell survival in response to ionizing radiation in a variety of experimental models including human
carcinoma, human
glioblastoma, and transformed mouse embryo fibroblast cell lines. We have introduced specific
antisense oligonucleotides into human mammary tumor cell lines in vitro to analyze the role of individual PKC
isoforms in radiation-induced cell death in
breast cancer. MDA-MB-231 and MCF-7 cells treated with
oligonucleotide directed against the PKC delta
isoform exhibited impaired survival in response to 5.6 Gy gamma-radiation as measured by mitochondrial metabolism of tetrazolium
dye. The role of PKC delta in the
breast tumor cell lines was of particular interest, because contradictory reports exist in the literature regarding the role of PKC delta in cell survival and apoptosis. A comparison of the effects of the PKC delta
antisense oligonucleotide and a
nucleotide scrambled version of this
nucleotide revealed only the
antisense oligonucleotide decreased cell survival. The PKC delta
antisense oligonucleotide decreased cell survival after exposure to low (1.5 Gy) radiation doses and in the absence of radiation insult. We found 3 micro M
rottlerin, a selective PKC delta inhibitor, to reduce MCF-7 and MDA-MB-231 cell survival. Furthermore, MCF-7 cells transformed to express a dominant-negative mutant of PKC delta exhibited reduced survival. Comet analysis showed that PKC delta
oligonucleotide treatment caused an accumulation of cells containing damaged
DNA similar to that seen in 1.5 Gy radiation-treated cells. We conclude that PKC delta acts as a prosurvival factor in human
breast tumor cells in vitro.