Inhibition of potentially anti-apoptotic proteins by antisense protein kinase C-alpha (Isis 3521) and antisense bcl-2 (G3139) phosphorothioate oligodeoxynucleotides: Relationship to the decreased viability of T24 bladder andPC3 prostate cancer cells

Isis 3521 and G3139 are 20- and 18-mer phosphorothioate oligonucleotides, r espectively, targeted to the protein kinase C (PKC)-alpha and bcl-2 mRNAs. Treatment of T24 bladder and PC3 prostate carcinoma cells with full-length and 3'-truncation mutants of Isis 3521 causes down-regulation of PKC-a prot ein and mRNA. However, at the level of a 15-mer and shorter, downregulation of mRNA expression is no longer observed. Further, no diminution in cellul ar viability, as measured by 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetra zolium bromide assay, in response to increasing concentrations of paclitaxe l, can be observed for these shorter oligomers. These observations not only indicate that PKC-alpha protein expression can be down-regulated by both R Nase H-dependent and -independent mechanisms but also that down-regulation of PKC-alpha is insufficient by itself to "chemosensitize" cells. G3139, wh ich down-regulates bcl-2 protein and mRNA expression, also down-regulates P KC-alpha protein and mRNA expression but not that of PKC-beta1, -epsilon, o r -zeta. However, the down-regulation of PKC-alpha and bcl-2 are not linked . When the carrier Eufectin 5 is employed, only bcl-2 is down-regulated in both T24 and PC3 cells at 50 nM oligonucleotide concentration. At 100 nM, b oth bcl-2 and PKC-alpha expression are down-regulated, and only at this con centration can "chemosensitization" to paclitaxel and carboplatin be observ ed. In contrast, the down-regulation of bcl-2 seems to be linked with that of RelA (p65). However, this too is also not sufficient for chemosensitizat ion, even though it leads to the loss of expression of genes under the puta tive control of nuclear factor-kappaB and to detachment of the cells from p lastic surfaces. These results underscore the complexity of the intracellul ar requirements for the initiation of chemosensitization to anti-neoplastic agents.