CONSTITUTIVE EXPRESSION OF PROSTAGLANDIN ENDOPEROXIDE G H SYNTHETASE (PGHS)-2 BUT NOT PGHS-1 IN HUMAN TRACHEAL EPITHELIAL-CELLS IN-VITRO/

Primary cultures of human tracheal epithelial (HTE) cells cultured in vitro, in defined serum-free media, express prostaglandin endoperoxide G/H synthase (PGHS) activity and produce prostaglandin E(2) (PGE(2)). In contrast to every other cell type studied to date, HTE cells appea r to constitutively express PGHS-2, the 'inducible' form of the enzyme , while expressing Little or no PGHS-1, the 'housekeeping' isoenzyme i n vitro. Prostaglandin synthesis in HTE cells was reduced by a selecti ve PGHS-2 inhibitor, N-[2-cyclohexyloyl-4-nitrophenyl] methane-sulfona mide (NS398), with an IC50 of approximately 1 mu M. Immunoblotting and immunoprecipitation of enzymatic activity with isozyme-specific antis era revealed only the PGHS-2 isoform. Full length human cDNA probes de tected only PGHS-2 message in Northern blots. Neither PGHS-2 activity nor mRNA levels were dependent on, nor stimulated by peptide growth fa ctors present in the defined serum-free growth medium, or by serum. Pr olonged maintenance in the absence of retinoic acid, however, lead to a decline in PGHS activity. Phorbol-myristate acetate (PMA) induced PG HS-2 activity and mRNA and neither PMA-induced, nor constitutive PGHS- 2 expression was suppressed by corticosteroids. Actinomycin D-treatmen t for six hours reduced the PGHS-2 activity and mRNA to only 50% that of untreated cells, suggesting that PGHS-2 mRNA is extremely stable in these cells. HTE cells, at least in vitro, appear unique among prosta glandin-producing cells in that they express PGHS-2, constitutively, i ndependent of regulation by growth factors, serum, or corticosteroids and fail to express PGHS-1 under any culture condition studied.