The human keratinocyte line SCC-9 has been used as a model for arsenate- induced perturbations of differentiation. Growth of these cells in 10 μM arsenate permitted the cultures to reach confluence, but prevented expression of 6 markers of suprabasal differentiation (involucrin, loricrin, filaggrin, spr 1, keratin 1 and keratin 10) as assayed by Northern blotting. By contrast, only slight alterations in mRNA levels were observed for one differentiation marker (keratinocyte transglutaminase) and for keratin 5, keratin 14. AP2 or glyceraldehyde phosphate dehydrogenase. The transition metal oxyanions vanadate and chromate had essentially the same suppressive effect on these markers as arsenate, while chronic treatment with tetradecanoylphorbol acetate was generally less effective in suppressing differentiation. To determine whether the previously observed arsenate- mediated alteration in AP1 and AP2 activities could account for the suppression of involucrin, a promoter analysis was conducted. Putative API and AP2 response elements were identified in regions important for transcriptional activity of the 5-flanking DNA. Mutations in two API sites and one AP2 site were observed to decrease promoter activity significantly, and in combination, to reduce it to κ 10% of that conferred by the native sequence. These results lend support to the working hypothesis thai arsenate suppresses involucrin expression, and, more generally, keratinocyte programming, by altering the transcription factors API and AP2.
- Phorbol ester
ASJC Scopus subject areas
- Health, Toxicology and Mutagenesis