title: BNIP2 extra long inhibits RhoA and cellular transformation by Lbc RhoGEF via its BCH domain.
abstract: Increased expression of BCH-motif-containing molecule at the C-terminal region 1 (BMCC1) correlates with a favourable prognosis in neuroblastoma, but the underlying mechanism remains unknown. We here isolated BNIPXL (BNIP2 Extra Long) as a single contig of the extended, in-vitro-assembled BMCC1. Here, we show that in addition to homophilic interactions, the BNIP2 and Cdc42GAP homology (BCH) domain of BNIPXL interacts with specific conformers of RhoA and also mediates association with the catalytic DH-PH domains of Lbc, a RhoA-specific guanine nucleotide exchange factor (RhoGEF). BNIPXL does not recognize the constitutive active G14V and Q63L mutants of RhoA but targets the fast-cycling F30L and the dominant-negative T19N mutants. A second region at the N-terminus of BNIPXL also targets the proline-rich region of Lbc. Whereas overexpression of BNIPXL reduces active RhoA levels, knockdown of BNIPXL expression has the reverse effect. Consequently, BNIPXL inhibits Lbc-induced oncogenic transformation. Interestingly, BNIPXL can also interact with RhoC, but not with RhoB. Given the importance of RhoA and RhoGEF signaling in tumorigenesis, BNIPXL could suppress cellular transformation by preventing sustained Rho activation in concert with restricting RhoA and Lbc binding via its BCH domain. This could provide a general mechanism for regulating RhoGEFs and their target GTPases.
authors.affiliation: Cell Signaling and Developmental Biology Laboratory, Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543, Republic of Singapore.
authors.forename: Unice J K
authors.initials: UJ
authors.lastname: Soh
authors.forename: Boon Chuan
authors.initials: BC
authors.lastname: Low
mesh_terms: D054758:A Kinase Anchor Proteins / Q000378:metabolism*; D000595:Amino Acid Sequence; D020134:Catalytic Domain; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D015778:Minor Histocompatibility Antigens; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D009363:Neoplasm Proteins / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D064067:Rho Guanine Nucleotide Exchange Factors; D017386:Sequence Homology, Amino Acid; D014162:Transfection; D020741:rho GTP-Binding Proteins / Q000378:metabolism; D020742:rhoA GTP-Binding Protein / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020743:rhoB GTP-Binding Protein / Q000378:metabolism; D000075024:rhoC GTP-Binding Protein
chemical_list: D054758:A Kinase Anchor Proteins; C085467:AKAP13 protein, human; D020662:Guanine Nucleotide Exchange Factors; D015778:Minor Histocompatibility Antigens; D050505:Mutant Proteins; D009363:Neoplasm Proteins; C509845:PRUNE2 protein, human; D011518:Proto-Oncogene Proteins; D064067:Rho Guanine Nucleotide Exchange Factors; C066737:RHOA protein, human; C066690:RHOC protein, human; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein; D020743:rhoB GTP-Binding Protein; D000075024:rhoC GTP-Binding Protein