TUMOR PROMOTER-INDUCED RELEASE AND METABOLISM OF ARACHIDONIC-ACID - COMPARISON BETWEEN MOUSE AND HUMAN EPIDERMAL-CELLS

Arachidonic acid (AA) release and metabolism to prostaglandins (PG) in response to the complete mouse skin tumour promoter 12-O-tetradecanoy lphorbol-13-acetate (TPA) and the first-stage promoter A23187 were com pared in keratinocytes from normal adult human and two different strai ns of mouse with different sensitivities to TPA as a tumour promoter. The rate, extent and distribution of incorporated [C-14]AA among the c lasses of phospholipids were similar in cultures of either CD-1, SSIN or human keratinocytes. Using prelabelled cultures, the amount of radi olabel released in control cultures was nearly identical for human and both strains of mice. Distinct species differences were observed, how ever, after TPA treatment. Cultures of human epidermal keratinocytes ( HEK) released only half as much label by 6 hr compared with either str ain of mouse. In addition, whereas the mouse epidermal keratinocytes ( MEK) metabolized AA readily to PGE2, very little PGE2 could be detecte d in the human cultures. The extent of variability between individual human samples (n = 11) in response to 0.1-mu-g TPA/ml ranged from a 20 % increase to a 200% increase in release of label, with a mean increas e of 50%, whereas murine cells produced a mean increase of 400%. When MEK and HEK were stimulated with 10(-6) and 10(-5) M-A23187, an increa se in the release of arachidonate by 200 and 400%, respectively, was o bserved for both species. Under these conditions of equal release, equ ivalent amounts of PGE2 were produced. To compare further the ability of mouse and human cells to metabolize exogenous AA to PGE2, freshly i solated, as well as cultured, cells from each species were incubated w ith [C-14]arachidonate. Under both conditions, HEK have approximately the same ability as MEK to metabolize AA to PGE2 (approx. 2% of the ar achidonate for both species). The reduced ability of HEK, compared wit h MEK, to produce PGE2 is specific to TPA and is due primarily to insu fficient substrate, that is, low levels of arachidonic acid release.