Expression of alcohol dehydrogenase 3 in tissue and cultured cells from human oral mucosa

Because formaldehyde exposure has been shown to induce pathological changes in human oral mucosa, eg, micronuclei, the potential enzymatic defense by alcohol dehydrogenase 3 (ADH3)/glutathione-dependent formaldehyde dehydroge nase was characterized in oral tissue specimens and cell lines using RNA hy bridization and immunological methods as well as enzyme activity measuremen ts. ADH3 mRNA was expressed in basal and parabasal cell layers of oral epit helium, whereas the protein was detected throughout the cell, layers. ADH3 mRNA and protein were further detected in homogenates of oral tissue and va rious oral cell cultures, including, normal, SV40T antigen-immortalized, an d tumor keratinocyte lines. inhibition of the growth of normal keratinocyte s by maintenance at confluency significantly decreased the amount of ADH3 m RNA, a transcript with a determined half-life of 7 hours. In contrast, deca y of ADH3 protein was not observed throughout a 4-day period in normal kera tinocytes, In samples from both tissue and cells, the ADH3 protein content correlated to oxidizing activity for the ADH3-specific substrate S-hydroxym ethylglutathione. The composite analyses associates ADH3 mRNA primarily to proliferative keratinocytes where it exhibits a comparatively short half-li fe, In contrast, the ADH3 protein is extremely stable, and consequently Is retained during the keratinocyte life span In oral mucosa, Finally, substan tial capacity for formaldehyde detoxification is shown from quantitative as sessments of alcohol- and aldehyde-oxidizing activities including K-m deter minations, indicating that ADH3 is the major enzyme involved in formaldehyd e oxidation in oral mucosa.