DECREASED LEVELS OF PROTEIN-KINASE-C ENZYME-ACTIVITY AND PROTEIN-KINASE-C MESSENGER-RNA IN PRIMARY COLON TUMORS

We have previously reported decreased protein kinase C (PKC) enzyme ac tivity in primary human colorectal carcinomas. The purpose of this stu dy was to extend these findings to a larger number of cases and to als o examine the levels of expression of mRNAs that encode specific isofo rms of PKC in these tumors. METHODS: Colorectal carcinomas and paired grossly normal adjacent mucosal samples were collected from 39 patient s. Complete histopathologic analyses were performed on all samples. PK C enzyme activity in both the cytosolic and particulate fractions was quantitated by measuring the amount of P-32 incorporated into histone Type III-S. Northern blot nucleic acid hybridization was performed usi ng polyA+ RNA extracted from both the tumor and normal tissue samples and P-32-labeled probes for specific isoforms of PKC. The paired sampl e t-test was used to determine the statistical significance of tumor t o normal ratios of both enzyme activity and mRNA levels. RESULTS: The mean value for cellular PKC enzyme activity in the colon tumors from 3 9 patients was about 60 percent of that found in the paired adjacent g rossly normal mucosa samples (P < 0.001). The subcellular distribution of PKC activity was similar in normal and tumor samples (about 70 per cent in the particulate fraction). The abundance of PKCalpha mRNAs var ied considerably among 28 tumor/normal pairs, with a mean tumor to nor mal (T:N) ratio of 1.0 +/- 0.6 for the 9.9-kb mRNA band and 1.4 +/- 0. 7 for the 3.5-kb band. The abundance of PKCbeta mRNAs was decreased in 30 of 39 tumors, with a mean T:N ratio of 0.6 +/- 0.4 for both the 9. 4- and 3.5-kb bands for all 39 samples (P < 0.001). None of the parame ters measured correlated with Dukes stage or the grade of the tumor. C ONCLUSIONS: These studies extend previous evidence that total PKC enzy me activity is frequently decreased in primary human colon tumors. Our finding that this is often associated with decreased levels of PKCbet a mRNA suggest that this is not simply due to post-translational down- regulation of this enzyme system. Further studies are required to dete rmine whether these changes in PKCalpha and PKCbeta mRNAs are due to a ltered de novo transcription or mRNA stability. It will also be of int erest to examine the expression of other isoforms of PKC in colon tumo rs.