Altered intracellular trafficking of EGFR by extracellular glucose concentration in squamous carcinoma cells (948.2)

Cancer cells usually exhibit the increased uptake of glucose than normal cells via glucose transporters, and pathogenesis and progression of squamous cell carcinoma are closely related to the expression of epidermal growth factor receptor (EGFR). To connect these two events, we here examined whether intracellular translocation of EGFR is regulated by glucose concentration. Human gingival, tongue and skin squamous carcinoma cells (HSC‐2, HSC‐3 and A431) were grown in D‐MEM in the presence of either high or low concentration of glucose (25mM or 5.5mM: HG or LG). When cancer cells were maintained in HG medium, the expression of EGFR with a molecular size of 170kDa was observed as assessed by Western blot analysis. In contrast, cells cultured in LG medium showed the major positive band to anti‐EGFR antibody, with 140kDa. We assumed the size difference is caused by glycosylation, as the treatment of cell extract with 170kDa band by N‐glycosidase produced the band with 140kDa. We further examined the effect of tunicamycin (10μM) to inhibit glycosylation process, resulting in that EGFR turned into 140kDa even if cells were cultured in HG medium. Biotinylation assay revealed that the only 170kDa protein was detected, indicating that the 170kDa bands are present at the plasma membrane. These results suggest that glucose concentration regulates glycosylation of EGFR and subsequent translocation to the plasma membrane.