Siew Wee Chan‡1, Chun Jye Lim‡, Fusheng Guo‡, Ivan Tan‡, Thomas Leung‡, and Wanjin Hong‡§2
‡ Institute of Molecular and Cell Biology, 61 Biopolis Drive, Singapore 138673
§ Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore,
8 Medical Drive, Block MD7, #02-03, Singapore 117597, Republic of Singapore
1&2 To whom correspondence may be addressed.
Published in Journal of Biological Chemistry on 27 December 2013.
Hippo pathway has become an important signaling pathway controlling tissue growth by regulating cell growth, proliferation and apoptosis. Dysregulation of the Hippo pathway is linked to human cancers. The central components of the pathway consist of core kinase complex (Mst1/2 and Lats1/2 with adaptor proteins WW45 and Mob1) and downstream transcriptional coactivators (YAP and TAZ). Once activated, the core kinase Lats1/2 phosphorylates and inactivates YAP and TAZ. Phosphorylated YAP and TAZ are translocated to cytoplasm and no longer able to activate transcription of the genes that are required for cell growth and cell proliferation. Whether Hippo pathway has downstream targets other than YAP and TAZ is unknown. In this report, we have identified upstream regulators of the Hippo pathway, Angiomotin (Amot) family members, as novel substrates of Hippo core kinases. The N-terminal regions of Amot proteins contain conserved HxRxxS consensus sites for Lats1/2-mediated phosphorylation. In vivo and in vitro studies show that Amot proteins can be phosphorylated by Lats1/2. Wild type and non-phosphorylated Amot were targeted to actin filaments, whereas phospho mimic Amot failed to be localized with actin. Overexpression of Lats1/2 caused dissociation of Amot from actin but not the non-phosphorylated Amot. Non-phosphorylated Amot promoted whereas Amot and phospho mimic Amot inhibited cell proliferation. These results collectively suggest that Hippo pathway negatively regulates actin-binding and cell proliferation of Amot proteins. Our group is one of the four groups that show Lats1/2 is able to regulate Hippo pathway upstream regulator Amot proteins, besides YAP/TAZ, through phosphorylation.
Figure Legend: A hypothetical working model showing how phosphoylation of Amot by Hippo core kinases affects its localization, interaction with the actin cytoskeleton, and regulation of cell proliferation
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