guanosine-triphosphate and Head-and-Neck-Neoplasms

In this study we investigated the correlation between RhoC expression and cancer stem cells (CSCs) formation in head and neck squamous cell carcinoma (HNSCC). The inhibition of RhoC function was achieved using shRNA. The expression of stem cell surface markers, ALDH and CD44 were significantly low in two RhoC depleted HNSCC cell carcinoma cell lines. Furthermore, a striking reduction in tumorsphere formation was achieved in RhoC knockdown lines. The mRNA expression of RhoC in RhoC knockdown adherent and tumorspheres are dramatically down regulated as compared with the scrambled control. The mRNA expression of stem cell transcription factors; nanog, oct3/4 (Pouf1), and sox2 were significantly depleted in RhoC knockdown clones. Further, the phosphorylation of STAT3(ser727), and STAT3(tyr705) were significantly down regulated in RhoC knockdown clones. The overexpression of STAT3 in RhoC knockdown did not show any change in expression patterns of either-STAT3(tyr705) or stem cell transcription factors, signifying the role of RhoC in STAT3 activation and thus the expression of nanog, oct3/4 and sox2 in HNSCC. The expression of Inter leukin-6 (IL-6) in RhoC knockdown HNSCC cell lines was dramatically low as compared to the scrambled control. Further, we have shown a rescue in STAT3 phosphorylation by IL-6 stimulation in RhoC knockdown lines. This study is the first of its kind to establish the involvement of RhoC in STAT3 phosphorylation and hence in promoting the activation of core cancer stem cells (CSCs) transcription factors. These findings suggest that RhoC may be a novel target for HNSCC therapy.

Topics: Aldehyde Dehydrogenase 1 Family; Carcinoma, Squamous Cell; Cell Line, Tumor; Gene Expression Regulation, Neoplastic; Guanosine Triphosphate; Head and Neck Neoplasms; Humans; Hyaluronan Receptors; Interleukin-6; Isoenzymes; Neoplastic Stem Cells; Phosphorylation; Retinal Dehydrogenase; rho GTP-Binding Proteins; rhoC GTP-Binding Protein; RNA, Small Interfering; Signal Transduction; STAT3 Transcription Factor; Transcription Factors

Previously we showed that galanin, a neuropeptide, is secreted by human squamous cell carcinoma of the head and neck (SCCHN) in which it exhibits an autocrine mitogenic effect. We also showed that rap1, a ras-like signaling protein, is a critical mediator of SCCHN progression. Given the emerging importance of the galanin cascade in regulating proliferation and survival, we investigated the effect of GAL on SCCHN progression via induction of galanin receptor 2 (GALR2)-mediated rap1 activation. Studies were performed in multiple SCCHN cell lines by inducing endogenous GALR2, by stably overexpressing GALR2 and by downregulating endogenous GALR2 with siGALR2. Cell proliferation and survival, mediated by the ERK and AKT signaling cascades, respectively, were evaluated by functional and immunoblot analysis. The role of rap1 in GALR2-mediated proliferation and survival was evaluated by modulating expression. Finally, the effect of GALR2 on tumor growth was determined. GALR2 stimulated proliferation and survival via ERK and AKT activation, respectively. Knockdown or inactivation of rap1 inhibited GALR2-induced, AKT and ERK-mediated survival and proliferation. Overexpression of GALR2 promoted tumor growth in vivo. GALR2 promotes proliferation and survival in vitro, and promotes tumor growth in vivo, consistent with an oncogenic role for GALR2 in SCCHN.

Topics: Animals; Apoptosis; Carcinoma, Squamous Cell; Cell Line, Tumor; Cell Proliferation; Cell Survival; Enzyme Activation; Extracellular Signal-Regulated MAP Kinases; Gene Expression Regulation, Neoplastic; GTPase-Activating Proteins; Guanosine Triphosphate; Head and Neck Neoplasms; Humans; Mice; Mice, Nude; Neoplasm Transplantation; Phosphorylation; Protein Processing, Post-Translational; Proto-Oncogene Proteins c-akt; Receptor, Galanin, Type 2; RNA, Messenger; Transplantation, Heterologous; Tumor Burden