Targeted Knockdown of SEPT9_v1 Inhibits Tumor Growth and Angiogenesis of Human Prostate Cancer Cells Concomitant with Disruption of Hypoxia-Inducible Factor-1 Pathway

Abstract

Hypoxia-inducible factor-1 (HIF-1) is a key transcription factor in the hypoxic response pathway. We recently identified a novel interaction between HIF-1α and the mammalian septin family member, septin 9 protein, isoform 1 (SEPT9_i1), a protein product of septin 9 transcript variant 1 (SEPT9_v1). Septins are a highly conserved family of GTP-binding cytoskeletal proteins that are implicated in multiple cellular functions, including oncogenesis. SEPT9_i1 binds and stabilizes HIF-1α protein and stimulates HIF-1 transcriptional activity by preventing its RACK1-mediated ubiquitination and degradation. SEPT9_i1-HIF-1 activation promotes tumor growth and angiogenesis. The effect of SEPT9_v1 silencing in prostate cancer cells was studied. SEPT9_v1 stable knockdown was generated in PC-3 cells using a specific shRNA. SEPT9_v1 silencing reduced HIF-1α protein expression and inhibited HIF-1 transcriptional activity. SEPT9_v1 knockdown affected cell morphology, deregulated cell cycle, and decreased migration. The antiproliferative effect of shSEPT9_v1 was abolished in HIF-1α knockout colon cancer cells. In vivo, SEPT9_i1 depletion reduced HIF-1α protein expression, cellular proliferation, tumor growth, and angiogenesis. These results provide new insights and validation for applying SEPT9_v1 as a potential target for antitumor therapy by interrupting the HIF-1 pathway. Mol Cancer Res; 8(5); 643-52. ©2010 AACR.

Septin roles in tumorigenesis

“…The interaction of overexpressed SEPT9_v1 with HIF-1a in prostate cancer results in increased cell proliferation and tumor angiogenesis, whereas the knockdown of SEPT9_v1 is associated with an increase in HIF-1a degradation, a decrease in HIF-1 transcriptional activity, cell proliferation and angiogenesis. Collectively, these findings suggest and support a significant role of this interaction in prostate tumor progression (Amir et al, 2006(Amir et al, , 2010.…”

“…The outcome of these rearrangements is the loss of the variable region at the N-terminus of the protein that characterizes SEPT9 isoforms _v1 and _v2. Interestingly, although the function of SEPT9 isoform variants in tumorigenesis remains largely unknown, the evidence supporting an oncogenic role for _v1 seems quite compelling (Gonzalez et al, 2007;Amir et al, 2010). It is intriguing that the MLL fusion proteins lose the genomic region responsible for the genetic variation of the SEPT9_v1 isoform, which seems to be required for its oncogenic properties in solid tumors.…”

“…Different septins are expressed at various levels in different tissues (Table 4). To date, septins have been found to exhibit altered expression or cellular localization in hormonally regulated tumors such as prostate (Amir et al, 2010), ovary (Burrows et al, 2003) and breast (Montagna et al, 2003;Gonzalez et al, 2007). The deregulation of septins has also been reported in oral/head and neck cancer (Kato et al, 2007;Bennett et al, 2008;Stanbery et al, 2010), melanoma (Jaeger et al, 2007), renal cell carcinoma (Craven et al, 2006a,b), gastrointestinal carcinoma (Kang et al, 2006), pancreatic tumors (Capurso et al, 2005) and hepatocellular carcinoma Kakehashi et al, 2010).…”

Septin 9 negatively regulates ubiquitin-dependent downregulation of epidermal growth factor receptor

“…1G). Of note, long SEPT9 isoforms have been shown to be upregulated in various tumors and cancer cell lines (Amir et al, 2010;Connolly et al, 2014;Connolly et al, 2011b;Stanbery et al, 2010). It remains to be determined whether and to what extent their interaction with CIN85 might contribute to cancer progression.…”

Septin 9 hypermethylation contributes to migration and resistance to drug treatments in colon cancer

“…Recent studies have shown that septin 9 promotes angiogenesis and facilitate tumor growth in the hetero-transplant model [9]. In contrast, breast cancer-related studies have indicated distinct cellular functions and suggested a tumor-suppressor role [10].…”