The Axin1 scaffold protein promotes formation of a degradation complex for c-Myc.

Expression of the c-Myc proto-oncoprotein is tightly regulated in normal cells. Phosphorylation at two conserved residues, threonine58 (T58) and serine62 (S62), regulates c-Myc protein stability. In cancer cells, c-Myc can become aberrantly stabilized associated with altered T58 and S62 phosphorylation. A complex signalling cascade involving GSK3beta kinase, the Pin1 prolyl ...
isomerase, and the PP2A-B56alpha phosphatase controls phosphorylation at these sites. We report here a novel role for the tumour suppressor scaffold protein Axin1 in facilitating the formation of a degradation complex for c-Myc containing GSK3beta, Pin1, and PP2A-B56alpha. Although knockdown of Axin1 decreases the association of c-Myc with these proteins, reduces T58 and enhances S62 phosphorylation, and increases c-Myc stability, acute expression of Axin1 reduces c-Myc levels and suppresses c-Myc transcriptional activity. Moreover, the regulation of c-Myc by Axin1 is impaired in several tested cancer cell lines with known stabilization of c-Myc or loss of Axin1. This study provides critical insight into the regulation of c-Myc expression, how this can be disrupted in three cancer types, and adds to our knowledge of the tumour suppressor activity of Axin1.
Mesh Terms:
Cell Line, E2F2 Transcription Factor, Glycogen Synthase Kinase 3, Humans, Peptidylprolyl Isomerase, Phosphorylation, Promoter Regions, Genetic, Protein Binding, Protein Phosphatase 2, Protein Structure, Tertiary, Proto-Oncogene Proteins c-myc, Repressor Proteins, Signal Transduction, Transcriptional Activation, Tumor Suppressor Proteins, Ubiquitination
EMBO J.
Date: Mar. 04, 2009
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