Downregulation of β-catenin by p53 involves changes in the rate of β-catenin phosphorylation and Axin dynamics

Abstract

b-Catenin, a structural component of cell-cell adhesions, is also a potent signaling molecule in the Wnt pathway activating target genes together with Lef/Tcf transcription factors. In colorectal and many other types of cancer, b-catenin is hyperactive owing to mutations in b-catenin, or in components regulating b-catenin degradation. Deregulated b-catenin can cause the activation of p53, a key tumor suppressor mutated in most cancers. Activated p53 can feed back and downregulate b-catenin. Here we investigated the mechanisms involved in downregulation of b-catenin by p53. We found that the p53-mediated reduction in b-catenin involves enhanced phosphorylation of b-catenin on key NH 2 -terminal serines and requires CK1 and GSK-3b activities, both being components of the b-catenin degradation machinery. Mutations in these NH 2 -terminal b-catenin serines blocked the ability of p53 to enhance the turnover of b-catenin. p53 also induced a shift in the distribution of the scaffold molecule Axin to a Triton X-100-soluble fraction, and led to depletion of b-catenin from this Triton-soluble fraction. The majority of Axin and phosphorylated b-catenin, however, colocalized in Triton X-100-insoluble punctate aggregates near the plasma membrane, and kinetics studies indicated that in the presence of p53 the movement of Axin into and out of the Triton X-100-insoluble fraction is accelerated. These results suggest that p53 induces a faster mobilization of Axin into the degradation complex thereby enhancing b-catenin turnover as part of a protective mechanism against the development of cancer.

Epigenetic silencing of AXIN2/betaTrCP and deregulation of p53-mediated control lead to wild-type β-catenin nuclear accumulation in lung tumorigenesis

“…Therefore, detailed mutational analysis on AXIN2 and betaTrCP genes can provide a better understanding of lung tumorigenesis. (Levina et al, 2004). Our study confirms that the effect of p53-mediated reduction in b-catenin level can also be exerted by The notion that destruction complex and p53 protein modulate the level of b-catenin was also supported by our clinical data.…”

Recruitment of adenomatous polyposis coli and β-catenin to axin-puncta

“…Using a commercially available polyclonal axin antibody, we observed endogenous axin in distinct puncta in the cytoplasm of Madin-Darby canine kidney (MDCK) cells (Figures 1b and c). Both endogenous and recombinant axin puncta were evenly distributed throughout the cytoplasm (Figures 1b-e), consistent with previous reports for endogenous axin in HEK293 cells (Levina et al, 2004;Wiechens et al, 2004) and recombinant axin (Fagotto et al, 1999;Smalley et al, 1999;Schwarz-Romond et al, 2005, 2007b. Axin-RFP was localized to cytoplasmic puncta when expressed in both MDCK ( Figure 1e) and HEK293 T cells (Supplementary Figures S1, S2).…”

“…In Xenopus the physiological concentration of axin is proposed to be exceedingly low (Lee et al, 2003), making detection at the subcellular level difficult. Endogenous axin has been detected in small, punctate cytoplasmic structures that redistribute to large aggregates close to the plasma membrane following treatment with LiCl (which inhibits GSK3-b, mimicking Wnt activation) (Levina et al, 2004;Wiechens et al, 2004). Ectopically expressed recombinant axin is localized in cytoplasmic vesicles or puncta (Fagotto et al, 1999;Smalley et al, 1999;Schwarz-Romond et al, 2005).…”

P53 levels determine outcome during β-catenin tumor initiation and metastasis in the mammary gland and male germ cells

“…However, in addition to regulating the expression of these oncogenes, b-catenin increases the activity of P53 by inducing P19 ARF expression (Damalas et al, 1999(Damalas et al, , 2001. This increase in P53 activity stimulates two independent feedback loops, acting through Axin/APC/ GSK3b and Siah-1/SIP/Ebi, to degrade b-catenin and attenuate its signaling (Liu et al, 2001;Matsuzawa and Reed, 2001;Sadot et al, 2001;Levina et al, 2004). However, each of these feedback loops require functional APC and binding to the N-terminal region of b-catenin.…”

“…P53 promotes proteolysis of b-catenin through activation of two separate ubiquitylation complexes. P53 effects Axin dynamics and increases the activity of the traditional APC/Axin/GSK3b complex thereby increasing the degradation rate of b-catenin (Levina et al, 2004). In addition, P53 induces the expression of a member of the Siah-1 family, Siah-1L, which forms a complex with SIP and Ebi resulting in ubiquitylation and degradation of b-catenin (Liu et al, 2001;Matsuzawa and Reed, 2001;Sadot et al, 2001).…”