Response of Carcinogen-Altered Mouse Epidermal Cells to Phorbol Ester Tumor Promoters and Calcium

Primary cultures of mouse epidermal cells are induced to terminally differentiate when extracellular calcium levels are increased to more than 0.1mM After carcinogen treatment, cellular foci can be selected that resist this calcium signal to terminally differentiate Calcium causes these foci to stratify, however, in contrast to normal epidermis, DNA- synthesizing cells in these foci are found in the suprabasal cell layers as well as in basal cells Cell lines derived from these foci may be considered to be putative initiated cells Three of these cell lines, designated 308, D, and F, have been characterized for their response to calcium and phorbol ester tumor promoters. The formation of cornified cells and the activity of epidermal transglutaminase were utilized as markers of epidermal differentiation. Neither calcium nor the tumor promoter 12-O-tetradecanoylphorbol-13- acetate (TPA) increased transglutaminase activity or cornification of any of the 3 lines Proliferation was estimated by the [3H]thymidine labeling index, by incorporation of [3H]thymidine into DNA, and by a clonal growth assay. Unlike primary normal cultures, rising the calcium level of the medium did not markedly reduce the rate of proliferation of any of the 3 cell lines. in 2 of the lines, line 308 and line D, proliferation increased in response to TPA exposure. in line F, [3H]thymidine incorporation in confluent cultures was inhibited by TRA, while in cells plated at clonal densities, TPA was cytotoxic at doses of 5 ng/ml or higher. If these calcium-resistant epidermal cell lines correspond to initiated cells, their lack of sensitivity to the induction of terminal differentiation by TPA could account for their growth relative to normal cells. Those lines that also respond to stimulation of proliferation by TPA to a greater extent than normal cells would have a further growth advantage

Selenoproteins Are Essential for Proper Keratinocyte Function and Skin Development

Dietary selenium is known to protect skin against UV-induced damage and cancer and its topical application improves skin surface parameters in humans, while selenium deficiency compromises protective antioxidant enzymes in skin. Furthermore, skin and hair abnormalities in humans and rodents may be caused by selenium deficiency, which are overcome by dietary selenium supplementation. Most important biological functions of selenium are attributed to selenoproteins, proteins containing selenium in the form of the amino acid, selenocysteine (Sec). Sec insertion into proteins depends on Sec tRNA; thus, knocking out the Sec tRNA gene (Trsp) ablates selenoprotein expression. We generated mice with targeted removal of selenoproteins in keratin 14 (K14) expressing cells and their differentiated descendents. The knockout progeny had a runt phenotype, developed skin abnormalities and experienced premature death. Lack of selenoproteins in epidermal cells led to the development of hyperplastic epidermis and aberrant hair follicle morphogenesis, accompanied by progressive alopecia after birth. Further analyses revealed that selenoproteins are essential antioxidants in skin and unveiled their role in keratinocyte growth and viability. This study links severe selenoprotein deficiency to abnormalities in skin and hair and provides genetic evidence for the role of these proteins in keratinocyte function and cutaneous development

Phorbol Esters Stimulate Dna-synthesis And Ornithine Decarboxylase Activity In Mouse Epidermal-cell Cultures

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62729/1/262402a0.pd