The Product of par-4, a Gene Induced during Apoptosis, Interacts Selectively with the Atypical Isoforms of Protein Kinase C

Abstract

The atypical PKCs are involved in a number of important cellular functions, including cell proliferation. We report here that the product of the par-4 gene specifically interacts with the regulatory domains of zeta PKC and lambda/LPKC, which dramatically inhibits their enzymatic activity. This is particularly challenging, because expression of par-4 has been shown to correlate with growth inhibition and apoptosis. Results are shown here demonstrating that the expression of par-4 in NIH-3T3 cells induces morphological changes typical of apoptosis, which are abrogated by cotransfection of either wild-type zeta PKC or lambda/LPKC, but not by their respective kinase-inactive mutants. These findings support a role for the atypical PKC subspecies in the control of cell growth and survival.

Interaction partners of Dlk/ZIP kinase: co-expression of Dlk/ZIP kinase and Par-4 results in cytoplasmic retention and apoptosis

“…Interestingly, Par-4 was also found as interaction partner of PKC isoforms x and l/i using a similar twohybrid approach (Diaz-Meco et al, 1996). This study showed that Par-4 speci®cally inhibits PKC isoforms x and l/i but not others, thereby interrupting signaling to AP1 and inducing apoptosis (Berra et al, 1997).…”

“…Par-4 (prostate apoptosis response gene 4) was originally identi®ed as a response gene induced upon induction of apoptosis in prostate carcinoma cells (Sells et al, 1994), and later on as interaction partner of transcription factor WT1, the Wilm's tumor gene product (Johnstone et al, 1996) and of PKC isoforms l/i and z (Diaz-Meco et al, 1996). Par-4 contains a leucine zipper which mediates its interaction with the zinc ®ngers of WT1 and PKC l/i/z.…”

“…The rationale behind this was the assumption that induction of apoptosis would require complete nuclear exclusion of Dlk, as achieved by excess Par-4. Since there are some discrepancies to other reports showing that both Dlk/ZIP kinase and Par-4 are capable of inducing apoptosis on their own in NIH3T3 cells (Kawai et al, 1998;Diaz-Meco et al, 1996) we included these mouse ®broblasts in our study. Dlk and Par-4 were expressed in REF52 and NIH3T3 cells at ratios of 1 : 1, 1 : 0.3, or 0.3 : 1 (based on the amounts of expression plasmids used for transfection).…”

“…Thus, leucine zippers may interact with other structural entities, too. Indeed, Par-4 itself can interact with zinc ®ngers of WT1 (Johnstone et al, 1996) and PKCx, and l/i (Diaz- Meco et al, 1996), fos can bind to the pocket domain of Rb (Nead et al, 1998), and ATF1 can interact with the catalytic subunit of protein kinase CKII (Yamaguchi et al, 1998).…”

Taxonomy and function of C1 protein kinase C homology domains

“…It is possible that protein kinase Cg binds ceramide at its CI domain by a mechanism analogous to diacylglycerol binding by typical PKCs. Atypical CI domains of protein kinase C< and CL have also been implicated in protein-protein interactions (Diaz-Meco et al, 1996a, 1996b. Human protein kinase C p (known as protein kinase D in mouse) contains a catalytic domain which is more similar to Dicfyosteliurn myosin light-chain kinase than to other protein kinase Cs, and was initially classified as an atypical isozyme.…”