2001 Volume 24 Issue 9 Pages 973-977
Protein kinase C δ (PKC δ) plays a key regulatory role in a variety of cellular functions, including apoptosis, as well as cell growth and differentiation. We previously reported that apoptosis was induced by pretreatment with 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), an inhibitor of PKC, in mouse thymocytes. In the present study, we showed that a novel PKC δ isoform (PKC δII) was transiently expressed when thymocytes were pretreated with H-7. The analysis of the cDNA encoding PKC δII indicated that a 78 bp fragment was inserted into the caspase-3 sensitive site of the original PKC δ (PKC δI), presumably by alternative splicing. The PKC δII expressed in COS-1 cells was one product with a molecular mass of 81 kDa and with kinase activity similar to that of PKC δI. The expressed PKC δI protein (78 kDa) was in part cleaved into a 38 kDa fragment in vivo and in vitro, but the PKC δII protein was not. Cleavage of the PKC δI protein was inhibited by a specific inhibitor of caspase-3, indicating that PKC δII is insensitive to caspase-3. The PKC δII was highly expressed in the testis and ovary, and at a lower level in the thymocytes, brain and kidney, whereas PKC δI was detected in most tissues, suggesting that the function of PKC δII is different from that of PKC δI.