Expression of growth arrest-specific (Gas) genes in murine keratinocytes: Gas2 is specifically regulated.

In order to elucidate a possible role of growth arrest-specific (gas) genes in the regulation of tissue proliferation, we analyzed their expression in keratinocytes isolated from murine back skin. On the mRNA level gas1, gas5, and gas6 were found to be significantly expressed whereas there was a relatively low expression of gas2, gas3, and gas4. Using keratinocytes fractionated according to their density resulted in subpopulations of cells: differentiating suprabasal cells in fractions I and II; proliferative basal cells in fractions IIIa, III and IV. We found gas2 protein to be expressed more strongly in the proliferative cells than in the differentiating cells. Stimulation of hyperproliferation by 12-O-tetradecanoylphorbol-13-acetate (TPA) resulted in a transient increase of gas2 protein content concomitantly with the time of maximal cell renewal. In this respect the murine keratinocyte cell line MSCP5 resembled freshly isolated keratinocytes. There was a higher expression of gas2 protein during exponential growth than during growth arrest, induced either by serum starvation or by TGFbeta treatment. Since, in contrast to the results reported for 3T3 cells, growth arrest within these cells was not accompanied by an elevation of gas2 protein, we suggest a cell-specific regulation of its expression.