Restoration of XAF1 expression induces apoptosis and inhibits tumor growth in gastric cancer

Abstract

XAF1 (XIAP-associated factor 1) is a novel XIAP binding protein that can antagonize XIAP and sensitize cells to other cell death triggers. Our previous results have shown that aberrant hypermethylation of the CpG sites in XAF1 promoter is strongly associated with lower expression of XAF1 in gastric cancers. In our study, we investigated the effect of restoration of XAF1 expression on growth of gastric cancers. We found that the restoration of XAF1 expression suppressed anchorage-dependent and -independent growth and increased sensitivity to TRAIL and druginduced apoptosis. Stable cell clones expressing XAF1 exhibited delayed tumor initiation in nude mice. Restoration of XAF1 expression mediated by adenovirus vector greatly increased apoptosis in gastric cancer cell lines in a time-and dose-dependent manner and sensitized cancer cells to TRAIL and drugs-induced apoptosis. Adeno-XAF1 transduction induced cell cycle G2/M arrest and upregulated the expression of p21 and downregulated the expression of cyclin B1 and cdc2. Notably, adeno-XAF1 treatment significantly inhibited tumor growth, strongly enhanced the antitumor activity of TRAIL in a gastric cancer xenograft model in vivo, and significantly prolonged the survival time of animals bearing tumor xenografts. Complete eradication of established tumors was achieved on combined treatment with adeno-XAF1 and TRAIL. Our results document that the restoration of XAF1 inhibits gastric tumorigenesis and tumor growth and that XAF1 is a promising candidate for cancer gene therapy. ' UICCKey words: XAF1; TRAIL; adenovirus; apoptosis; tumorigenesis; cell cycle arrest; gastric cancer; gene therapy The development of cancer is a result of aberrant cellular proliferation and failure of these cells to undergo apoptosis in response to normal signaling cues. 1 Dysregulation of cell death pathways has been termed a 'hallmarkÕ of cancer 2 and is required for tumor initiation, progression and drug resistance. 3,4 Virtually all known apoptosis signal pathways converge on the caspases. 5 The inhibitor of apoptosis (IAP) genes encode a family of proteins that bind and inactivate key caspases involved in the initiation (Caspase-9) and execution (Caspase-3 and -7) of this cascade. 6 An elevated expression level of XIAP, the most potent of the mammalian IAPs, is associated with tumor resistance to cell death cues. 7,8 Thus the strategies that target XIAP synthesis or function are under investigation for the treatment of cancer. 9 Both antisense 10,11 and small molecule inhibitors of XIAP function 12,13 have demonstrated promise in animal models of human cancer.XAF1 has been previously identified as a XIAP binding partner. 13 XAF1 directly interacts with endogenous XIAP and results in XIAP sequestration in nuclear inclusions. XAF1 antagonizes the anticaspase activity of XIAP and reverses the protective effect of XIAP overexpression in cell lines. 13 XAF1 does not contain an amino terminal tetrapeptide motif analogous to Smac/DIABLO or Omi, suggesting that its mechanism of IAP interaction ...

Tumor suppressor XAF1 induces apoptosis, inhibits angiogenesis and inhibits tumor growth in hepatocellular carcinoma

“…Cytochrome c is an important factor involved in mitochondria apoptotic pathway (intrinsic pathway). Our results suggest that Ad5/F35-XAF1 induces apoptosis of liver cancer cells through both endogenous and exogenous pathways, supporting our previous reports that XAF1 induces apoptosis in gastric and colon cancer cells [29, 30]. …”

“…The restoration of XAF1 expression has been shown to induce cell apoptosis in gastric and colorectal cancer cell lines and strengthen the apoptotic effects of chemotherapeutic drugs and TNF Related Apoptosis Inducing Ligand (TRAIL) [29, 30]. Gene therapy for recombinant adenovirus vector mediated XAF1 significantly suppressed tumor growth in gastric and colon cancer in vitro and in vivo [29-31]. Qi et al [40] also reported that XAF1 had potent antitumor activity when it was delivered by conditionally replicated adenovirus vector ZD55.…”

“…Our previous studies have shown that XAF1 induced apoptosis through intrinsic and extrinsic apoptosis pathways in gastric and colon cancer cells [29, 30]. We have found that XAF1 induces autophagy by upregulating beclin 1 and inhibiting AKT pathway [31].…”

Expression of apoptosis-related proteins and its clinical implication in surgically resected gastric carcinoma

“…Studies have proven that IAP overexpression is generally correlated with poor prognosis [11][12][13]. In gastric carcinoma (GC), one or several protein expressions of survivin, caspase family, XIAP, XAF1, Smac/DIABLO, and Bcl-2 were evaluated [14][15][16][17][18][19]. However, to our knowledge, multiple protein expression, expressional correlation, and their clinical significance have not been simultaneously evaluated.…”

Stimulation of the hypoxia pathway modulates chemotherapy resistance in Hodgkin’s lymphoma cells

“…The restoration of XAF1 expression leads to apoptosis in cancer cells and suppresses tumor growth. In hepatocellular carcinomas, the increased expression of XAF1 leads to an inhibition of tumor angiogenesis [64,67,68]. In ovarian carcinoma and colorectal cancer cells, the overexpression of XAF1 leads to a sensitization of the cells for cisplatin [69,70].…”