Evidence for involvement of yeast proliferating cell nuclear antigen in DNA mismatch repair

DNA mismatch repair plays a key role in the maintenance of genetic fidelity. Mutations in the human mismatch repair genes hMSH2, hMLH1, hPMS1, and hPMS2 are associated with hereditary nonpolyposis colorectal cancer. The proliferating cell nuclear antigen (PCNA) is essential for DNA replication, where it acts as a processivity factor. Here, we identify a point mutation, pol30-104, in the Saccharomyces cerevisiae POL30 gene encoding PCNA that increases the rate of instability of simple repetitive DNA sequences and raises the rate of spontaneous forward mutation. Epistasis analyses with mutations in mismatch repair genes MSH2, MLH1, and PMS1 suggest that the pol30-104 mutation impairs MSH2/MLH1/PMS1-dependent mismatch repair, consistent with the hypothesis that PCNA functions in mismatch repair. MSH2 functions in mismatch repair with either MSH3 or MSH6, and the MSH2-MSH3 and MSH2-MSH6 heterodimers have a role in the recognition of DNA mismatches. Consistent with the genetic data, we find specific interaction of PCNA with the MSH2-MSH3 heterodimer.     

The zeta isoform of protein kinase C controls interleukin-2-mediated proliferation in a murine T cell line: evidence for an additional role of protein kinase C epsilon and beta

In order to address a role of protein kinase C in signal transduction through interleukin-2, interleukin-4, and interleukin-9 receptors, we took advantage of the availability of a selective protein kinase C inhibitor, GF109203X, and the availability of TS1 beta and TS1 alpha beta cell lines which can be maintained in interleukin-2, interleukin-4, or interleukin-9 independently. In this report we report that inhibition of protein kinase C activity by GF109203X does not block interleukin-4- or interleukin-9-dependent proliferation and, on the contrary, does block interleukin-2-dependent proliferation, suggesting that interleukin-4 and interleukin-9 do not use signal transduction pathways mediated by protein kinase C and that the common gamma chain of interleukin-2, interleukin-4, and interleukin-9 receptors is not responsible per se for the activation of protein kinase C through interleukin-2 receptor. Moreover, GF109203X induces apoptosis in cells cultured in interleukin-2 but not in interleukin-4 or interleukin-9. Using antisense oligonucleotides, we report that the zeta and epsilon protein kinase C isoforms are involved in signaling through high-affinity interleukin-2 receptor and beta and zeta are involved in signaling through intermediate-affinity interleukin-2 receptor. Taken together, our data indicate that activation of the zeta, beta, and epsilon protein kinase C isoforms is an important step in interleukin-2-mediated proliferation.