Menin-mediated caspase 8 expression in suppressing multiple endocrine neoplasia type 1

Abstract

Multiple endocrine neoplasia type 1 (MEN1) is a familial tumor syndrome linked to mutation of the MEN1 gene, which encodes a tumor suppressor, menin. We previously reported that menin up-regulates the caspase 8 expression and promotes TNF-α-induced apoptosis. However, it remains unclear how menin up-regulates caspase 8 expression and whether meninmediated caspase 8 expression plays a role in repressing MEN1 development. Here we show that menin binds the 5′-untranslated region (5′-UTR) of the Caspase 8 locus in vivo and activates transcription of a reporter gene through the 5′-UTR. Menin directly binds the 5′-UTR in a sequence-independent manner in vitro. Moreover, Men1 ablation in cells reduces acetylation of histones H3 and H4 at the 5′-UTR of the caspase 8 locus bound by menin in vivo. Notably, the MEN1-derived menin point mutants lose their ability to bind the caspase 8 locus and fail to induce caspase 8 expression and TNF-α-mediated apoptosis. Consistent with these observations, the expression level of caspase 8 is markedly reduced in insulinomas from Men1+/- mice. Together, our results indicate that menin enhances the caspase 8 expression by binding the caspase 8 locus, and suggest that menin suppresses MEN1 tumorigenesis, at least in part, by up-regulating caspase 8 expression. © 2007 by The American Society for Biochemistry and Molecular Biology, Inc.