[Expression analysis of EGFR and SGLT1 in oral squamous cell carcinoma]

Overexpression of epidermal growth factor receptor (EGFR) is known to be associated with poor prognosis in malignant tumors. Sodium-glucose co-transporter 1 (SGLT1) is a membrane protein that transports glucose across cellular membranes. Recently, EGFR has been shown to stabilize SGLT1 and promote glucose uptake into cancer cells. The purpose of this study was to investigate the coexpression of EGFR and SGLT1 and their relationships with clinicopathological features in oral squamous cell carcinoma (OSCC). Total cell lysates from OSCC cell lines were prepared to check the protein expression of EGFR and SGLT1 by western blotting assay. Both proteins can be detected and the expression levels of SGLT1 were significantly correlated with those of EGFR. Pearson's product-moment correlation coefficient was 0.89 (p = 0.016). Transient overexpression of EGFR in HeLa cells showed that SGLT1 expression was increased by EGFR, suggesting that EGFR can stabilize the protein stability of SGLT1. To see whether mRNA expression of SGLT1 is correlated with protein expression, real-time PCR was performed. The results revealed no compatible expression between mRNA and protein, indicating that this discrepancy is caused by the post-transcriptional modification. Immunohistochemical staining using surgical specimens from 52 tongue SCC patients also showed a significant correlation between EGFR and SGLT1 expression. Moreover, EGFR/SGLT1 expression was inversely correlated with tumor differentiation (p = 0.004). These results indicate that EGFR/SGLT1 coexpression may contribute to the growth and survival of OSCC, but further study is needed to clarify the implication of these proteins in the manifestation of malignancy and clinical significance.