Hsp70 incompletely disaggregates misfolded K488X-menin to promote tumourigenesis in a family with multiple endocrine neoplasia type 1

Multiple endocrine neoplasia type 1 (MEN1) is caused by germline mutations in the MEN1 gene, including nonsense mutations and missense variants, which result in the formation of truncated inactive menin protein and some of which cause degradation of mutant menin proteins. Here, we describe a c.1462 A > T (p.K488X) mutation in exon 10 of MEN1 as a potential pathogenic mutation in an extended Chinese family with MEN1. We observed that K488X-menin was degraded by ubiquitination modification resulting from the combined actions of carboxy-terminus of Hsc70-interacting protein (CHIP) and Heat Shock Protein Family 70 (Hsp70) in vitro. K488X-menin is a misfolded truncated protein that results in amyloid aggregation in live cells and affected tissues, which is promoted by Hsp70 and/or CHIP. Although Hsp70 can inhibit the aggregation of K488X-menin in vitro, it is not upregulated in the affected tissues in patients with MEN1, and thus cannot completely disaggregate the aggregated K488X-menin. Further, we found that K488X-menin triggers early tumourigenesis in a MEN1 mutant zebrafish model. Moreover, K488X-menin disaggregation was induced by Hsp70 activator and Hsp70 was upregulated in homozygous mutant zebrafish. Our findings provide a novel biophysical mechanism involving Hsp70 underlying MEN1 tumourigenesis in a Chinese family with MEN1.