The carboxy terminus of p53 mimics the polylysine effect of protein kinase CK2-catalyzed MDM2 phosphorylation

Abstract

The oncogene product MDM2 can be phosphorylated by protein kinase CK2 in vitro 0.5 ± 1 mol of phosphate were incorporated per mol MDM2 protein. The catalytic subunit of protein kinase CK2 (a-subunit) catalyzed the incorporation of twice as much phosphate into the MDM2 protein as it was obtained with the holoenzyme. Polylysine stimulated MDM2 phosphorylation by CK2 holoenzyme threefold in contrast to the a-subunitcatalyzed MDM2 phosphorylation which was reduced by about 66% when polylysine was added. Full length p53, but also a peptide representing a C-terminal fragment of the tumor suppressor gene product p53 (amino acids 264 ± 393 which also harbors the CK2b interaction site at amino acids 287 ± 340) mimicked the polylysine e ect in all respects, ie. stimulation of phosphate incorporation by CK2 holoenzyme and inhibition in the presence of the catalytic CK2 a-subunit. Stimulation by p53 264 ± 393 was on the average close to twofold and inhibition in the case of the a-subunitcatalyzed MDM2 phosphorylation was about 40%. Phosphorylation of MDM2 by CK2 holoenzyme in the presence of the p21 WAF1/CIP1 , known to be a potent inhibitor of cyclin-dependent protein kinases, also led to a signi®cant reduction of phosphate incorporation into MDM2 indicating that p21 WAF1/CIP1 does not exclusively inhibit cell cycle kinases. Furthermore, these data add new insight into the autoregulatory loop which include p21 WAF1/CIP1 , MDM2 protein, CK2 and p53.

p53-dependent apoptosis or growth arrest induced by different forms of radiation in U2OS cells: p21WAF1/CIP1 repression in UV induced apoptosis

“…In this work inactivation of the p21 WAF1/CIP1 gene converted the growth arrest response to an apoptotic response implying a protective eect of p21 binds to and inhibits the activity of most cyclin-cdk complexes, thereby preventing phosphorylation of downstream substrates such as Rb (Harper et al, 1993;Xiong et al, 1993). However, p21 WAF1/CIP1 also inhibits the ability of casein kinase II to phosphorylate p53 at serine 392 (Guerra et al, 1997). Phosphorylation of this site after UV treatment is associated with increased DNA binding by p53 (Kapoor and Lozano, 1998;Lu et al, 1998).…”

Regulation and activation of p53 and its family members

“…In vitro experiments have shown that MDM2 can be phosphorylated by DNA-PK and that this phosphorylation blocks its association with p53. 63 MDM2 was found to be phosphorylated by casein kinase 2 in vitro, 64 although so far none of these results have been confirmed in vivo.…”

Protein kinase CK2 interacts with the splicing factor hPrp3p

“…As hPrp3p obviously binds to the catalytic subunits of CK2 independently of the regulatory b-subunit we were interested if the a-subunit is also able to phosphorylate the protein. However, the catalytic a-subunit alone was unable to phosphorylate hPrp3p (Figure 7a, lane 3 and 4) although the enzyme phosphorylated the CK2a substrate mdm2 (Guerra et al, 1997) (Figure 7a, lane 5). Next, we wanted to map the phosphorylation site on the polypeptide chain of hPrp3p.…”