BNIP-Sα 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-Sa 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-Sa 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 RhoAbinding 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-Sa could reduce p50RhoGAP binding to RhoA and restore RhoA activation. Furthermore, BNIP-Sa mutants lacking the RhoA-binding motif completely failed to induce cell rounding and apoptosis. Therefore, via unique binding motifs within its BCH domain, BNIP-Sa 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.

Cayman ataxia protein caytaxin is transported by kinesin along neurites through binding to kinesin light chains

“…So far, no biological activities have been assigned to the Nterminal regions of caytaxin, BNIP-2 and BNIP-S (Buschdorf et al, 2006;Qin et al, 2003;Zhou et al, 2005;Zhou et al, 2006). However, if the binding of caytaxin to KLCs has physiological significance, overexpression of the caytaxin N-terminal fragment might exert dominant-negative effects on the endogenous caytaxin.…”

“…If that is the case, it raises the possibility that the competition between KLC and CHIP and the consequent ubiquitylation and degradation of caytaxin exert an intriguing regulation of caytaxin functions. No biological activities had been assigned to the N-terminal regions of caytaxin, BNIP-2 or BNIP-S (Buschdorf et al, 2006;Qin et al, 2003;Zhou et al, 2005;Zhou et al, 2006). When overexpressed in non-neural cells such as MCF-7 cells, BNIP-2 and BNIP-S induce dramatic morphological changes and apoptosis (Zhou et al, 2002;Zhou et al, 2005;Zhou et al, 2006).…”

BNIP2 extra long inhibits RhoA and cellular transformation by Lbc RhoGEF via its BCH domain

“…BNIPXL BCH domain associates with RhoA and RhoC, but not RhoB, and elicits cell morphological changes Our previous work indicates that the BNIP2 BCH domain activates Cdc42 for cell protrusions (Zhou et al, 2005) whereas BNIP-Sα targets RhoA and Cdc42GAP/p50RhoGAP, leading to concerted RhoA activation and apoptosis (Zhou et al, 2002;Zhou et al, 2006). Phylogenetic analyses indicate that the BNIPXL BCH domain is highly homologous to that of BNIP2 and BNIP-Sα (supplementary material Fig.…”

“…For example, the BNIP2 BCH domain activates Cdc42 to elicit cell protrusions (Zhou et al, 2005) whereas the BNIP-Sα BCH domain sequesters Cdc42GAP/p50RhoGAP via heterophilic BCH interactions while targeting RhoA directly for further activation, leading to apoptosis (Zhou et al, 2002;Zhou et al, 2006). Furthermore, the BCH domain of BPGAP1, a close homolog of Cdc42GAP/p50RhoGAP, also promotes Cdc42-dependent short pseudopodia, which are necessary for cell migration (Shang et al, 2003;Lua and Low, 2004) and Ras/MAPK activation (Lua and Low, 2005).…”

Brain-specific BNIP-2-homology protein Caytaxin relocalises glutaminase to neurite terminals and reduces glutamate levels

“…BNIP-2 and BPGAP1) (Zhou et al, 2005a;Shang et al, 2003) or cell rounding during apoptosis (e.g. BNIP-S␣) (Zhou et al, 2002;Zhou et al, 2005b). It has been postulated that part of the BCH domain of BNIP-H that weakly resembles the CRAL/TRIO domain (a domain that binds small lipophilic molecules) might be important for targeting specific ligand for its normal function (Bomar et al, 2003).…”