Chemoprevention with Protein Kinase A RIα Antisense in DMBA-Mammary Carcinogenesis

摘要

Cancer is potentially preventable disease. A surprising variety of intracellular pathways can be a target for chemoprevention. Earlier it was dis-covered that cAMP-mediated system can play important role in prevention of DMBA-mammary carcinogenesis. There are two types of cAMP-dependent protein kinases (PKA), type I (PKA-I) and type II (PKA-II), which share a common catalytic (C) subunits, but contain distinct regulatory (R) ones, RI versus RII, respectively. Evidence suggests that increased expression of PKA-I and its regulatory subunit (RIα) correlates with tumorogenesis and tumor growth. It was found that downregulation of RIα by 21-mer antisense oligonu-cleotide led to growth arrest of cancer cells. The effect of RIα antisense oligo-nucleotide correlated with a decrease in RIα protein and a concomitant increase in RIIβ protein level. It was shown that antisense RIα can protect in a sequence-specific manner from 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary carcinogenesis. At 90 days after DMBA intubation, RIα-antisense-treated rats exhibited significantly lower number of tumors per rat, than untreated control animals. The antisense also delayed the first tumor ap-pearance. An increase in RIα and PKA-I levels in the mammary gland and liver preceded tumor production, and antisense downregulation of RIa restored normal levels of PKA-I and PKA-II in these tissues. Antisense RIa in the liver induced the phase II enzymes, glutathione S-transferase and quinone oxi-doreductase, c-fos protein, and activator protein-1 (AP-1)- and cAMP response element (CRE)-directed transcription. In the mammary gland, antisense RIα promoted DNA repair processes. In contrast, the CRE transcription-factor de-coy could not mimic these effects of antisense RIα. The results demonstrate that RIa antisense produces dual anticarcinogenic effects : (a) increasing DMBA detoxification in the liver by increasing phase II enzyme activities, in-creasing CRE-binding-protein phosphorylation and enhancing CRE- and AP-1 directed transcription; and (b) activating DNA repair processes in the mam-mary gland by downregulating of PKA-1.