Soh Unice J K, Low Boon Chuan
Cell Signaling and Developmental Biology Laboratory, Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543, Republic of Singapore.
J Cell Sci. 2008 May 15;121(Pt 10):1739-49. doi: 10.1242/jcs.021774. Epub 2008 Apr 29.
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.
含BCH基序分子在C端区域1（BMCC1）的表达增加与神经母细胞瘤的良好预后相关，但其潜在机制仍不清楚。我们在此分离出BNIPXL（BNIP2超长型）作为体外组装的扩展BMCC1的单一重叠群。在此，我们表明，除了嗜同性相互作用外，BNIPXL的BNIP2和Cdc42GAP同源性（BCH）结构域还与RhoA的特定构象体相互作用，并介导与RhoA特异性鸟嘌呤核苷酸交换因子（RhoGEF）Lbc的催化DH-PH结构域的结合。BNIPXL不识别RhoA的组成型活性G14V和Q63L突变体，而是靶向快速循环的F30L和显性负性T19N突变体。BNIPXL N端的第二个区域也靶向Lbc富含脯氨酸的区域。过表达BNIPXL会降低活性RhoA水平，而敲低BNIPXL表达则会产生相反效果。因此，BNIPXL抑制Lbc诱导的致癌转化。有趣的是，BNIPXL也可以与RhoC相互作用，但不与RhoB相互作用。鉴于RhoA和RhoGEF信号在肿瘤发生中的重要性，BNIPXL可以通过协同限制RhoA和Lbc结合，防止Rho持续激活，从而抑制细胞转化。这可能为调节RhoGEF及其靶标GTP酶提供一种通用机制。
