Posttranslational regulation of glucose-6-phosphate dehydrogenase activityin tongue epithelium

Expression of glucose-6-phosphate dehydrogenase (G6PD) activity is high in tongue epithelium, but its exact function is still unknown, it may be relat ed;either to the high proliferation rate of this tissue or to protection ag ainst oxidative stress. To elucidate its exact role, we localized quantitat ively G6PD activity, protein and mRNA using image analysis in tongue epithe lium of rat and rabbit, two species with different diets. Distribution patt erns of G6PD activity were largely similar in rat and rabbit but the activi ties were twofold lower in rabbit. Activity was two to three times higher i n upper cell layers of epithelium than in basal cell layers, whereas basal layers, where proliferation takes place, contained twice as much G6PD prote in and 40% more mRNA than upper layers. Our findings show that G6PD is synt hetized mainly in basal cell layers of tongue epithelium and that it is pos ttranslationally activated when cells move to upper layers. Therefore, we c onclude that the major function of G6PD activity in tongue epithelium is th e formation of NADPH for protection against oxidative stress and that diet affects enzyme expression in this tissue.