Editors' ChoiceCell Biology

Yap Methylated

Sci. Signal.  06 Aug 2013:
Vol. 6, Issue 287, pp. ec182
DOI: 10.1126/scisignal.2004590

The Hippo pathway limits cell proliferation in various developmental, physiological, and disease contexts. Signaling through the cascade of kinases in the Hippo pathway culminates in phosphorylation of the transcriptional coactivator Yap, which leads to its nuclear exclusion and subsequent degradation, thus preventing the expression of Yap-responsive genes that stimulate cell proliferation and inhibit apoptosis. Oudhoff et al. report that methylation of Yap in mouse intestinal epithelial cells (IECs) also promotes its cytoplasmic retention. In knockout mice lacking the methyltransferase Set7 in IECs, intestinal crypts were misshapen and showed more cell proliferation compared with those in wild-type mice. Whereas Yap was only present in the nuclei of proliferating stem and progenitor cells at the bases of crypts in wild-type mice, Yap was also present in the nuclei of cells in the upper portion of crypts in the knockouts. When isolated from animals, the mutant IECs had increased expression of Yap target genes compared with wild-type IECs. In cultured Set7–/– mouse embryonic fibroblasts (MEFs), high cell density failed to induce the cytoplasmic translocation of Yap and reduced expression of Yap target genes that were observed in wild-type MEFs. Whereas transgene-encoded, wild-type Set7 rescued cytoplasmic translocation and target gene down-regulation, a mutant form of Set7 lacking methyltransferase activity did not rescue these phenotypes. Further experiments in MEFs indicated that Set7 was required for cytoplasmic retention of Yap but not for its phosphorylation-dependent nuclear export or subsequent degradation. Set7 coimmunoprecipitated with endogenous Yap from MEF lysates, and immunoprecipitated Yap was monomethylated in lysates from wild-type, but not Set7–/–, MEFs. By mass spectrometry, epitope-tagged Yap isolated from HEK293 cells was methylated on Lys494. Mutating this Lys residue to Arg caused the resulting protein (YapK494R) to accumulate in the nucleus and an increased Yap target gene expression in MEFs. Set7 was present in the cytoplasm of confluent MEFs, suggesting a model in which Set7 methylates Yap in the cytoplasm to promote its retention, thus complementing the effects of Yap phosphorylation by kinases of the Hippo pathway.

M. J. Oudhoff, S. A. Freeman, A. L. Couzens, F. Antignano, E. Kuznetsova, P. H. Min, J. P. Northrop, B. Lehnertz, D. Barsyte-Lovejoy, M. Vedadi, C. H. Arrowsmith, H. Nishina, M. R. Gold, F. M. V. Rossi, A.-C. Gingras, C. Zaph, Control of the Hippo pathway by Set7-dependent methylation of Yap. Dev. Cell 26, 188–194 (2013). [PubMed]