Amir Sharon, Wang Ruoxiang, Simons Jonathan W, Mabjeesh Nicola J
Prostate Cancer Research Laboratory, Department of Urology, Tel Aviv Sourasky Medical Center, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 64239, Israel.
J Biol Chem. 2009 Apr 24;284(17):11142-51. doi: 10.1074/jbc.M808348200. Epub 2009 Feb 26.
A critical mediator of the cellular response to hypoxia is hypoxia-inducible factor 1 (HIF-1). Increased levels of HIF-1alpha are often associated with increased tumor metastasis, therapeutic resistance, and poorer prognosis. We recently identified a novel interaction between HIF-1alpha and the mammalian septin family member, SEPT9_v1. Septins are a highly conserved family of GTP-binding cytoskeletal proteins that are implicated in multiple cellular functions, including cell division and oncogenesis. SEPT9_v1 binds and stabilizes HIF-1alpha protein and stimulates HIF-1 transcriptional activity. SEPT9_v1-HIF-1 activation promotes tumor growth and angiogenesis. The structural and functional relationships between SEPT9_v1 and HIF-1alpha were analyzed. We found that SEPT9_v1 binds specifically with HIF-1alpha but not with HIF-2alpha. The GTPase domain of SEPT9_v1 was identified as essential for HIF-1alpha binding. A GTPase domain-derived polypeptide, corresponding to amino acids 252-379, was able to disrupt HIF-1alpha-SEPT9_v1 interaction and to inhibit HIF-1 transcriptional activity. SEPT9_v1 also protected HIF-1alpha from degradation induced by HSP90 inhibition by preventing the interaction of HIF-1alpha with the RACK1 protein, which promotes its oxygen-independent proteasomal degradation. In conclusion, a new mechanism of oxygen-independent activation of HIF-1 has been identified that is mediated by SEPT9_v1 blockade of RACK1 activity on HIF-1alpha degradation.
细胞对缺氧反应的关键介质是缺氧诱导因子1（HIF-1）。HIF-1α水平升高通常与肿瘤转移增加、治疗抵抗和预后较差相关。我们最近发现了HIF-1α与哺乳动物septin家族成员SEPT9_v1之间的一种新相互作用。Septin是一类高度保守的GTP结合细胞骨架蛋白家族，参与多种细胞功能，包括细胞分裂和肿瘤发生。SEPT9_v1结合并稳定HIF-1α蛋白，并刺激HIF-1转录活性。SEPT9_v1-HIF-1激活促进肿瘤生长和血管生成。分析了SEPT9_v1与HIF-1α之间的结构和功能关系。我们发现SEPT9_v1特异性地与HIF-1α结合，而不与HIF-2α结合。SEPT9_v1的GTPase结构域被确定为与HIF-1α结合所必需。一个对应于氨基酸252-379的GTPase结构域衍生多肽能够破坏HIF-1α-SEPT9_v1相互作用并抑制HIF-1转录活性。SEPT9_v1还通过阻止HIF-1α与促进其氧非依赖性蛋白酶体降解的RACK1蛋白相互作用，保护HIF-1α免受HSP90抑制诱导的降解。总之，已确定一种新的HIF-1氧非依赖性激活机制，该机制由SEPT9_v1对RACK1在HIF-1α降解上的活性的阻断介导。
