BPB : Vol. 24 (2001) , No. 9 973

Novel Protein Kinase C δ Isoform Insensitive to Caspase-3

Yoshiaki SAKURAI¹⁾, Yoshiaki ONISHI²⁾, Yutaka TANIMOTO¹⁾ and Harutoshi KIZAKI¹⁾

1) Department of Biochemistry, Tokyo Dental College
2) Institute of Molecular and Cell Biology, AIST

(Received March 23, 2001)
(Accepted June 18, 2001)

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.

Key words

protein kinase C δ; caspase-sensitivity; alternative splicing; thymocyte