title: The protein kinase Cdelta catalytic fragment is critical for maintenance of the G2/M DNA damage checkpoint.
abstract: Protein kinase Cdelta (PKCdelta) is an essential component of the intrinsic apoptotic program. Following DNA damage, such as exposure to UV radiation, PKCdelta is cleaved in a caspase-dependent manner, generating a constitutively active catalytic fragment (PKCdelta-cat), which is necessary and sufficient for keratinocyte apoptosis. We found that in addition to inducing apoptosis, expression of PKCdelta-cat caused a pronounced G(2)/M cell cycle arrest in both primary human keratinocytes and immortalized HaCaT cells. Consistent with a G(2)/M arrest, PKCdelta-cat induced phosphorylation of Cdk1 (Tyr(15)), a critical event in the G(2)/M checkpoint. Treatment with the ATM/ATR inhibitor caffeine was unable to prevent PKCdelta-cat-induced G(2)/M arrest, suggesting that PKCdelta-cat is functioning downstream of ATM/ATR in the G(2)/M checkpoint. To better understand the role of PKCdelta and PKCdelta-cat in the cell cycle response to DNA damage, we exposed wild-type and PKCdelta null mouse embryonic fibroblasts (MEFs) to UV radiation. Wild-type MEFs underwent a pronounced G(2)/M arrest, Cdk1 phosphorylation, and induction of apoptosis following UV exposure, whereas PKCdelta null MEFs were resistant to these effects. Expression of PKCdelta-green fluorescent protein, but not caspase-resistant or kinase-inactive PKCdelta, was able to restore G(2)/M checkpoint integrity in PKCdelta null MEFs. The function of PKCdelta in the DNA damage-induced G(2)/M cell cycle checkpoint may be a critical component of its tumor suppressor function.
authors.affiliation: Molecular and Cellular Biochemistry Program, Department of Cell Biology, Neurobiology, and Anatomy, Loyola University Chicago, Maywood, Illinois 60153, USA.
authors.forename: Edward L
authors.initials: EL
authors.lastname: LaGory
authors.forename: Leonid A
authors.initials: LA
authors.lastname: Sitailo
authors.forename: Mitchell F
authors.initials: MF
authors.lastname: Denning
mesh_terms: D000818:Animals; D055162:Biocatalysis; D020134:Catalytic Domain; D002455:Cell Division / Q000502:physiology* / Q000528:radiation effects; D002460:Cell Line; D004249:DNA Damage; D016195:G2 Phase / Q000502:physiology* / Q000528:radiation effects; D006801:Humans; D007231:Infant, Newborn; D051379:Mice; D051745:Protein Kinase C-delta / Q000737:chemistry* / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D014466:Ultraviolet Rays / Q000009:adverse effects
chemical_list: D051745:Protein Kinase C-delta