Molecular characterization of human homologs of yeast MOB1

Abstract

MOB (Mps One Binder) is a conserved gene family found in all major kingdoms.The MOB genes are essential components acting in mitotic exit and cytokinesis in both budding and fission yeasts. They are further identified as tumor suppressors in Drosophila (D.) melanogaster. Recently, they are found to be involved in the emerging Drosophila Hippo-LATS tumor suppressor pathway. Seven human homologs of yeast MOB (hMOB1A, 1B, 2A, 2B,3,4,5) have been discovered. The hMOB1B is the gene that has been extensively studied and is reported to be required for the activation of LATS (Large Tumor Suppressor)/NDR (Nuclear Dbf2-related) protein kinase family, however, the functional significance of the gene remains unknown. This study is the first to elucidate the biological and biochemical functions of all seven human MOBs. By examining hMOB mRNA expression in various human tissues, we found that the hMOBs have exhibited different expression patterns. We also investigated the subcellular localization of hMOBs during interphase through immunofluorescent analysis. While hMOB2A is localized in the cytoplasm, hMOB4 is exclusively found in the nucleus. All of the other hMOBs are localized in both cytoplasm and nucleus. Furthermore, we identified hMOB1A and hMOB1B as the main binding partners of LATS and NDR in vitro. Additionally, we successfully identified a region on hMOB1B for the interaction with LATS or NDR and determined the crucial residue that is responsible for the binding of LATS2 with hMOB1B. Most significantly, we found that over-expression of hMOB1B in human cancer cells inhibits cell proliferation and induces cell death.Moreover, hMOB1B when targeted to the plasma membrane dramatically enhances the iii phenotype. Conversely, small interfering (si) RNA-mediated suppression of either endogenous hMOB1A or hMOB1B causes increased cell proliferation, whereas suppression of both hMOB1A and hMOB1B demonstrates a more significant enhancement in tumor cell growth. Moreover, co-expression of both LATS and hMOB1B targeted to the plasma membrane completely abolishes cell proliferation. Our findings provide convincing evidence that hMOB1A and hMOB1B function as negative regulators of cell proliferation and as pro-apoptotic proteins. Understanding hMOBs functions in the cell and their possible role in tumorigenesis can provide important information for the diagnosis and treatment of human cancers.iv ACKNOWLEDGEMENTS

Itch E3 ubiquitin ligase regulates large tumor suppressor 1 stability

“…In particular, although many upstream activators of LATS, such as Hippo/MST and Mats/MOB1, have been reported (20)(21)(22), direct negative regulators of LATS are yet to be identified. In this study, we have provided convincing evidence that Itch E3 ubiquitin ligase is a bona fide binding partner and negative regulator of LATS1.…”

The Hippo pathway regulates stem cell proliferation, self-renewal, and differentiation

“…The activation of Mst1/2 leads to phosphorylation and activation of their direct substrates, Lats1/2 (Chan et al, 2005). Mob1, which forms a complex with Lats1/2 (Chow et al, 2010), is also phosphorylated and activated by Mst1/2, resulting in enhanced interaction between Lats1/2 and Mob1 (Hirabayashi et al, 2008;Praskova et al, 2008). Similar to that in Drosophila, MST1/2/Sav1 and Lats1/2/Mob1 form a physical and functional core of the Hippo pathway.…”

LATS tumor suppressor: A new governor of cellular homeostasis

“…37 As further evidence, in a recent paper, Chow et al confirmed that membrane-targeted activation of LATS1 by MOB1 significantly increases LATS1 kinase activity toward its substrate YAP. 42 Although from these studies it is clear that LATS1 kinase activity can be enhanced by membrane-targeting, it is not yet known if this is the only mechanism of LATS1 activation or if the same holds true for LATS2. In addition, since these studies only use ectopic expression of targeted proteins, it would be important to establish the dynamics of endogenous LATS in response to MOB1 expression.…”