Stability and Function of Mammalian Lethal Giant Larvae-1 Oncoprotein Are Regulated by the Scaffolding Protein RanBPM

Abstract

The evolutionarily conserved lethal giant larvae (Lgl) tumor suppressor gene has an essential role in establishing apical-basal cell polarity, cell proliferation, differentiation, and tissue organization. However, the precise molecular mechanism by which the Lgl carries out its function remains obscure. In the current study, we have identified Ran-binding protein M (RanBPM) as a novel binding partner of Mgl-1, a mammalian homolog of Drosophila tumor suppressor protein lethal (2) giant larvae (L(2)gl) by yeast two-hybrid screening. RanBPM seems to act as a scaffolding protein with a modulatory function with respect to Mgl-1. The Mgl-1 and RanBPM association was confirmed by co-immunoprecipitation and GST pull-down experiments. Additionally, expression of RanBPM resulted in inhibition of Mgl-1 degradation, and thereby extended the half-life of Mgl-1. Furthermore, the ability of Mgl-1 activity in cell migration and colony formation assay was enhanced by RanBPM. Taken together, our findings reveal that RanBPM plays a novel role in regulating Mgl-1 stability and contributes to its biological function as a tumor suppressor.The lethal giant larvae (Lgl) 2 gene was identified as the first recessive oncogene in Drosophila (1-3). Lgl function is reported to be essential for the development of polarized epithelia (4, 5), localization of cell fate determinant Numb in Drosophila neuroblasts (6, 7) and association with cytoskeletal complex (8). It also has been reported that Lgl prevents tumor formation by antagonizing Decapentaplegic (Dpp) signaling by semaphonrin 5c in the brain (9). Lgl functions in concert with two other tumor suppressor genes: discs large (dlg) and scribble (scrib), primarily involved in maintenance of basolateral membrane domain and basal protein targeting (4, 5, 7). In addition, Lgl functions competitively with Par3 in order to make a complex with Par6-aPKC protein complexes that are crucial for the apical membrane domain (10, 11).Homologs of Lgl have been identified in many species including human, mouse, rat, bovine, insect, worm, slime mold, and yeast (12-15). The two Lgl homologs, Lgl1 and Lgl2 have conserved function in the maintenance of cell polarity and tissue homeostasis. In mouse, changes in Lgl1 activity leads to the loss of apical junctional complex in neuroblasts and hyperplasia (16). Hugl-l, a human homolog of Lgl is strongly down-regulated in malignant melanoma (17). A significant reduction in the expression of Hugl-1 was reported in tumor tissues from colorectal cancer patients. Thus, down-regulation of Hugl-1 correlates with occurrence of colorectal cancers whereas its expression leads to increase in cell adhesion and decreased cell migration (18). Hugl-1 plays a key role in the regulation of proteins, which are involved in epithelial-mesenchymal transition (EMT), a process that enables an epithelial cell to gain mesenchymal and migratory properties (17). In mouse embryonic fibroblasts, a mutant of Mgl-1 lacking five serine residues reduced cell polarization in an in vitro wounding ass...

Pilot Study on “Pericytic Mimicry” and Potential Embryonic/Stem Cell Properties of Angiotropic Melanoma Cells Interacting with the Abluminal Vascular Surface

“…Interestingly, from the coculture of EC and MC versus simultaneously MC alone and EC alone, 17 genes from the 27 known differentially expressed genes were linked to migratory and/or embryonic/cancer stem cell properties: nine overexpressed genes: CCL2, ICAM1, SELE, IL6, TRAF1, SERPINB2, CXCL6, PDGFB and EVX1, and eight underexpressed genes: CFDP1, BLID, RGNEF, MALT1, RANBP9, UPF1, PLAA and ZXDC. More specifically, these genes have demonstrated properties linked to (i) cancer cell migration: CCL2 [26,27], ICAM1 [28], IL6 [29], RGNEF [30] and RANBP9 [31]; (ii) cancer progression and metastasis: CCL2 [26,27,32], ICAM1 [33,34], SELE [35,36], TRAF1 [37], IL6 [29], SERPINB2 [38], CXCL6 [39], BLID [40], MALT1 [41], UPF1 [42], PLAA [43], RGNEF [44], ZXDC [45]; (iii) EMT: CCL2 [46] and IL6 [29] ; and (iv) embryonic and/or cancer stem cell properties: CCL2 [46][47][48] , PDGFB [49] , EVX1 [50], CFDP1 [51] and RANBP9 [52] . Furthermore, the 15 most significantly enriched functional groups analyzed by IPA included: development, cell movement, cancer, and embryonic development.…”

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Evaluation of Lethal Giant Larvae as a Schistosomiasis Vaccine Candidate

“…The WD40 repeats of LGL form β -propellers that can act as protein-interacting modules for SCRIB, and the atypical protein kinase C- (aPKC-) mediated phosphorylation of LGL during epithelial polarity establishment is needed for its basolateral localization [5–9]. Many studies have shown that LGL function is essential for the development of polarized epithelia [7, 10–12], localization of cell-fate determinants, and association with the cytoskeletal complex [13, 14]. LGL was first described in the fruit fly Drosophila melanogaster as a neoplastic tumor suppressor gene [15, 16].…”