MEN1 tumor-suppressor protein localizes to telomeres during meiosis

Multiple endocrine neoplasia type I is an autosomal dominant cancer predisposition syndrome caused by mutations in the tumor-suppressor gene MEN1. The gene encodes a nuclear protein, menin, with no recognized functional motifs. Menin has been shown negatively to regulate transcriptional activation mediated by JunD, although the significance of this interaction in normal cell physiology and how the absence of menin leads to tumorigenesis are unknown. Menin is highly expressed in testes. We used immunocytochemistry to explore its role in meiosis and found that it localizes exclusively at telomeres. JunD was not found at telomeres in meiotic cells. In view of elevated telomerase activity or abnormal telomere structure in virtually all malignancies, regulation of telomere function would be an appealing role for a tumor suppressor. However, menin does not specifically associate with telomeres in somatic cells, as indicated by lack of co-localization with the known telomeric protein TRF2. Cells overexpressing menin had normal telomerase activity, and tumors with homozygous MEN1 mutations showed no aberrations in telomere length, indicating that menin does not directly regulate telomerase activity. The role of menin at meiotic telomeres appears to be independent of JunD and may not have a counterpart in somatic cells. These results suggest that menin may play different roles in different tissues through interactions with different proteins.