Comparative study of CYP1A1 induction by 3-methylcholanthrene in various human hepatic and epidermal cell types.

Hepatocytes and keratinocytes are among the most widely used cells in pharmaco-toxicology, but a limitation of these models is the provision of human tissues on a regular basis. The suitability of HepG2, HaCaT and HESV cell lines as an acceptable substitute for primary cultures was examined. In these cell types, the effects of 3-methylcholanthrene (3-MC) were analysed on CYP1A1 gene expression, a crucial CYP subfamily in the activation of chemical carcinogens. Ethoxyresorufin O-deethylase (EROD) activity was never detected in HESV cells, but in other cell types it was stimulated in a concentration-dependent manner (maximal induction, 1-2.5 mum). Above this peak induction the effect fell rapidly. Northern blot analysis of CYP1A1 mRNA agreed with the trends obtained for EROD values. However, the decrease of the EROD activity observed at the highest 3-MC concentrations was not correlated with CYP1A1 mRNA reduction. This study also demonstrated that 3-MC is capable of significantly inducing CYP1A1 in HaCaT cells (17-fold over control), as in human hepatocytes (six- to 18-fold) and HepG2 (fourfold). Therefore, in contrast to SV40-immortalized keratinocytes (HESV), spontaneously immortalized keratinocytes (HaCaT) may constitute a valuable tool for studying epidermal CYP1A1 gene regulation by xenobiotics.