Abstract 3359: Glucose regulated protein78, a putative head and neck cancer initiating cells marker

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Background: Head and neck squamous cell carcinoma (HNSCC) is a highly lethal cancer that contains cellular and functional heterogeneity. Previously, we enriched a subpopulation of highly tumorigenic head and neck cancer initiating cells (HN-CICs) from HNSCC cells (HNSCCs) using tumor sphere formation approach. GRP78, a stress-inducible endoplasmic reticulum (ER) chaperone, has been reported to play a role in the maintenance of embryonic stem cells and was up-regulated in enriched HN-CICs. However, the molecular mechanisms mediated by GRP78 to operate the physiological characteristics in HN-CICs remain unclear. Herein, we determined the critical role of GRP78 in the maintenance of stemness characteristics and tumorigenic phenotype in HNSCCs. Methods: First, Affymatrix microarray and two-dimensional differential gel electrophoresis (2-D DIGE) proteomic analyses were applied to identify GRP78 and membrane associated GRP78 (memGRP78) as a putative marker of HN-CICs. Flow cytometry cell sorting was used to isolate memGRP78+ cells and memGRP78− cells for evaluating CICs properties. Down-regulation of GRP78 expression in HNSCCs and HN-CICs were achieved by lentiviral-mediated small hairpin RNA interference (shRNAi), and the stemness characteristics in GRP78-knockdown HN-CICs were elucidated. In addition, in vitro tumorigenic properties between GRP78-knockdown and control HN-CICs were determined. The in vivo tumorigenicity of GRP78-knockdown HN-CICs was evaluated by xenotransplantation assay. Finally, we examined the correlation on expression of GRP78 and stemness genes in HNSCC patient tissues by immunohistochemical staining. Results: We identified that GRP78/memGRP78 was significantly up-regulated in enriched HN-CICs. Subsequently, memGRP78+ HNSCCs displayed CICs properties. Lentiviral mediated knockdown of GRP78 significantly reduced expression of stemness genes in HN-CICs and HNSCCs, but enhanced the differentiation capability of HN-CICs. Overall, down-regulation of GRP78 lessened tumorigenicity of HN-CICs both in vitro and in vivo. Conclusion: Our studies first elucidated the crucial role of GRP78 in the maintenance of stemness and tumorigenicity of HN-CICs. Notably, targeting GRP78 signaling might be a potential therapeutic target for HNSCC by eliminating CICs and memGRP78 could be a novel surface biomarker for isolation HN-CICs. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3359.