SAK/PLK4 is necessary for centriole duplication both in Drosophila and human cells. Drosophila cells tolerate the lack of centrioles and undertake mitosis but cannot form basal bodies and hence flagella. Human cells depleted of SAK show error-prone mitosis, likely to underlie its tumor-suppressor role.

1Glucagon-like peptide-1 (GLP-1), an insulinotropic and glucoincretin hormone, is a potentially important therapeutic agent in the treatment of diabetes. We previously provided evidence that GLP-1 induces pancreatic ␤-cell growth nonadditively with glucose in a phosphatidylinositol-3 kinase (PI-3K)-dependent manner. In the present study, we investigated the downstream effec-

We report here that the novel protein kinase C isoform, PKC␦, is required at or prior to the level of the mitochondria for apoptosis induced by a diverse group of cell toxins. We have used adenoviral expression of a kinase-dead (KD) mutant of PKC␦ to explore the requirement for PKC␦ in the mitochondrial-dependent apoptotic pathway. Expression of PKC␦KD, but not PKC␣KD, in salivary epithelial cells resulted in a dosedependent inhibition of apoptosis induced by etoposide, UV-irradiation, brefeldin A, and paclitaxel. DNA fragmentation was blocked up to 71% in parotid C5 cells infected with the PKC␦KD adenovirus, whereas caspase-3 activity was inhibited up to 65%. The activation of caspase-9-like proteases by all agents was also inhibited in parotid C5 cells expressing PKC␦KD. The ability of PKC␦KD to block the loss of mitochondrial membrane potential was similarly determined. Expression of PKC␦KD blocked the decrease in mitochondrial membrane potential observed in cells treated with etoposide, UV, brefeldin A, or paclitaxel in a dose-dependent manner. In contrast to the protective function of PKC␦KD, expression of PKC␦WT resulted in a potent induction of apoptosis, which could be inhibited by coinfection with PKC␦KD. These results suggest that PKC␦ is a common intermediate in mitochondrial-dependent apoptosis in salivary epithelial cells.

The cDNA for the monocarboxylate transporter MCT2 from rat testis has been cloned and sequenced. The derived protein sequence shows 82% identity with that from hamster. Rat MCT2 has a relative insertion of five amino acids in the N-terminal sequence preceding the first predicted transmembrane segment. MCT2 appears to be less highly conserved between species than MCT1. Using Northern blotting of RNA from rat and mouse tissues, MCT2 message was demonstrated to be abundant in the testis where a smaller, less abundant MCT2 transcript was also present. Low levels of a slightly different-sized transcript were found in rat and mouse liver, and mouse kidney. In hamster, only one-size transcript was detected at relatively high abundance in all the tissues examined. Antibodies were raised against a peptide derived from the extreme C-terminus of rat MCT2, and Western blotting with these detected MCT2 in membrane fractions prepared from rat testis, liver and brain but not those from heart or skeletal muscle. In hamster, MCT2 was detected in liver, heart and testis but not in brain [Garcia, Brown, Pathak, and Goldstein (1995) J. Biol. Chem. 270, 1843-1849]. For both rat MCT1 and MCT2 there were marked differences between the relative abundance of their respective messages and the amount of protein in membrane fractions from different tissues. This suggests that expression of both of these transporters in different tissues may be species-specific and regulated post-transcriptionally. The different-sized MCT2 transcripts may arise from alternative splicing. Starvation of rats for up to 48 h did not lead to any change in MCT1 or MCT2 expression in the liver, as determined by either Northern or Western blotting.