Abstract 2081: The unfolded protein response relieves stress in tumor cells by stimulating angiogenesis

Abstract

Abstract Abstract: During the avascular phase, tumor size is limited to 1-2 mm in diameter. When tumors exceed this size, the high stress imposed by limited glucose and oxygen in the microenvironment induces the unfolded protein response (UPR). Previous studies have shown that the UPR can promote survival, or activate apoptosis when there is prolonged or severe stress. Recent studies have suggested a role for the UPR in angiogenesis. However, the mechanism of UPR-regulated angiogenesis has not been extensively investigated. We hypothesize that tumor cells relieve stress caused by nutrient and oxygen deprivation by stimulating blood vessel growth via UPR-mediated induction of angiogenesis. To address this hypothesis, a human squamous cell carcinoma line, UM-SCC-81B, was subjected to glucose deprivation and mRNA array was used to evaluate expression of UPR proteins and angiogenesis mediators. This study revealed an increase in expression of several UPR proteins (Grp78, DDIT3, ATF3, ATF4, ATF6) ranging from 2 to 20-fold after 24 hours of glucose deprivation (0.1 mM glucose), and a 4.43, 3.06 and 2.59-fold increase in the expression of the pro-angiogenic VEGF, FGF2 and IL-6, respectively. Western blot, ELISA and q-PCR were used to verify these results. Western blot analysis showed a significant increase of Grp78 and DDIT3 protein expression. ELISA experiments revealed that after 24 hours of glucose deprivation, VEGF levels increased 3 folds as compared to the non-treated control, and that FGF2 and IL-6 were also upregulated (p < 0.05). q-PCR results further revealed that UPR markers (Grp78, DDIT3, ATF4) and angiogenesis mediators (VEGF, FGF2, IL-6) increased significantly (p < 0.05). Four other tumor cell lines (i.e. U87, glioma; MCF7, breast cancer; UM-SCC 11B and UM-SCC 17B, head and neck squamous carcinomas) were examined to determine the cell-type specificity of these responses. In all tumor cell lines examined, the upregulation of UPR proteins was associated with a significant increase in VEGF expression (p < 0.05). In conclusion, the UPR response is associated with the upregulation of critical pro-angiogenic factors in tumor cell lines. These data strongly suggest that targeting pathways involved in UPR regulation of angiogenesis is a promising strategy in combination with other conventional cancer therapies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2081. doi:10.1158/1538-7445.AM2011-2081