title: BNIP-Salpha induces cell rounding and apoptosis by displacing p50RhoGAP and facilitating RhoA activation via its unique motifs in the BNIP-2 and Cdc42GAP homology domain.
abstract: Changes in cell morphology are linked to many cellular events including cytokinesis, differentiation, migration and apoptosis. We recently showed that BNIP-Salpha induced cell rounding that leads to apoptosis via its BNIP-2 and Cdc42GAP Homology (BCH) domain, but the underlying mechanism has not been determined. Here, we have identified a unique region (amino acid 133-177) of the BNIP-Salpha BCH domain that targets RhoA, but not Cdc42 or Rac1 and only the dominant-negative form of RhoA could prevent the resultant cell rounding and apoptotic effect. The RhoA-binding region consists of two parts; one region (residues 133-147) that shows some homology to part of the RhoA switch I region and an adjacent sequence (residues 148-177) that resembles the REM class I RhoA-binding motif. The sequence 133-147 is also necessary for its heterophilic interaction with the BCH domain of the Rho GTPase-activating protein, p50RhoGAP/Cdc42GAP. These overlapping motifs allow tripartite competition such that overexpression of BNIP-Salpha could reduce p50RhoGAP binding to RhoA and restore RhoA activation. Furthermore, BNIP-Salpha mutants lacking the RhoA-binding motif completely failed to induce cell rounding and apoptosis. Therefore, via unique binding motifs within its BCH domain, BNIP-Salpha could interact and activate RhoA while preventing its inhibition by p50RhoGAP. This concerted mechanism could allow effective propagation of the RhoA pathway for cell rounding and apoptosis.
authors.affiliation: Cell Signaling and Developmental Biology Laboratory, Department of Biological Sciences, The National University of Singapore, Singapore, Republic of Singapore.
authors.forename: Y T
authors.initials: YT
authors.lastname: Zhou
authors.forename: G R
authors.initials: GR
authors.lastname: Guy
authors.forename: B C
authors.initials: BC
authors.lastname: Low
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry / Q000502:physiology*; D020816:Amino Acid Motifs; D017209:Apoptosis; D001665:Binding Sites; D045744:Cell Line, Tumor; D003599:Cytoskeleton / Q000737:chemistry; D020690:GTPase-Activating Proteins / Q000502:physiology*; D006801:Humans; D017434:Protein Structure, Tertiary; D020764:cdc42 GTP-Binding Protein / Q000737:chemistry*; D020742:rhoA GTP-Binding Protein / Q000737:chemistry / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C450834:BNIPL protein, human; D020690:GTPase-Activating Proteins; C085379:rho GTPase-activating protein; D020764:cdc42 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein