KERATINOCYTES STIMULATE PROSTAGLANDIN-I2 SYNTHESIS BY 3T3-CELLS AND EXHIBIT ENHANCED CORNIFICATION WHEN EXPOSED TO PROSTAGLANDIN-I2 ANALOGS

The predominant cyclooxygenase products of keratinocytes are prostaglandin (PG)E2 and PGF2-alpha with only trace amounts of PGl2 synthesis detected. When normal or immortal (NM1) keratinocytes were co-cultured with mitomycin C-treated 3T3 cells, increased synthesis of PGl2 was noted compared to mitomycin C-treated 3T3 cells alone. The PGl2 level in co-cultures was maximum within the first week and diminished rapidly thereafter. These results suggested keratinocytes enhance the production of PGl2 by 3T3 cells. Keratinocyte cultures incubated with lloprost and Piriprost, stable PGl2 analogues, showed evidence of increased cornification as demonstrated by staining with rhodanile blue, decreased shedding of cells into the culture medium, and more cornified material adhering to the culture surface. The cultures appeared to be responsive between the first and second weeks after plating and the inhibition of shedding could not be reversed by changing to drug-free medium. Control and treated cultures showed identical electrophoretic protein patterns. Immunoblots showed involucrin unchanged in extracts of control and treated cultures while the 22 kd pancornulin was absent in treated cultures. The findings that keratinocytes enhance the production of PGl2 by 3T3 cells and that PGl2 analogues enhance cornification of confluent keratinocytes raise the possibility that eicosanoids may serve as autoregulatory signals together with other factors.