MOUSE ENDOMETRIUM STROMAL CELLS EXPRESS A POLYCYCLIC AROMATIC HYDROCARBON-INDUCIBLE CYTOCHROME-P450 THAT CLOSELY RESEMBLES THE NOVEL P450 IN MOUSE EMBRYO FIBROBLASTS (P450EF)

Stromal cells from mouse endometrium, E041 cells, at passages 21, 23 a nd 26 were metabolically active towards 7,12-dimethylbenz[a]anthracene (DMBA). The total DMBA-metabolizing activity of E041 cells was prefer entially increased by benz[a]anthracene (BA) relative to 2,3,7,8-tetra chloro-dibenzo-p-dioxin (TCDD) treatment (7-fold by BA and 4-fold by T CDD), but the relative proportions of DMBA metabolites formed remained unchanged. Profiles of DMBA metabolites generated from E041 cell micr osomes were very different from that of mouse P4501A1 but exhibited si milarities to that of P450EF, the polycyclic aromatic hydrocarbon (PAH )-inducible cytochrome P450 in the mouse embryo fibroblast cell line C 3H10T1/2 (10T1/2). Notably, both induced and uninduced E041 cell micro somes were very effective in the formation of the proximate carcinogen DMBA-3,4-dihydrodiol (15-20% of total) and DMBA-10,11-dihydrodiol (13 -18% of total) but ineffective in forming the 7-hydroxymethyl derivati ve of DMBA (< 1% of total). Antibodies to P450EF completely inhibited the DMBA-metabolizing activities of both induced and uninduced E041 ce ll microsomes, with an effectiveness similar to that in microsomes pre pared from identically treated 10T1/2 celts. Anti-P4501A1 had no inhib itory effect on DMBA metabolism by either induced or uninduced E041 ce ll microsomes. Total DMBA-metabolizing activities in BA- and TCDD-indu ced E041 cells were consistently 2-fold lower compared to those in sim ilarly treated 10T1/2 cells. In addition, both induced and uninduced E 041 cell microsomes formed a lower proportion of DMBA dihydrodiols rel ative to phenols in comparison to identically treated 10T1/2 cell micr osomes (0.5 versus 1). Addition of exogenous epoxide hydrolase to E041 cell microsomes resulted in a product distribution indistinguishable from that in 10T1/2 cells. Immunoblots demonstrated 5-fold lower level s of epoxide hydrolase in E041 cell microsomes compared to 10T1/2 cell microsomes. Anti-P450EF immunoblotted a 55 kd protein in E041 cell mi crosomes that was induced 14-fold by BA and 6-fold by TCDD, thus paral leling the increases in the respective DMBA metabolism. It is therefor e concluded that following PAH exposure endometrial stromal cells expr ess the novel PAH-inducible mouse embryo fibroblast P450 and fail to e xpress P4501A1.