ABSTRACT:Cytochromes P450 (P450s) contribute to the metabolic activation and inactivation of various endogenous substrates. Despite years of research, the physiological role of CYP2S1 remains unknown. CYP2S1 has demonstrated NADPH P450-reductase-independent metabolism of cyclooxygenase (COX)-derived prostaglandins [e.g., prostaglandin G 2 (PGG 2 )] at nanomolar concentrations. Arachidonic acid is converted to prostaglandin precursors [PGG 2 and prostaglandin H 2 (PGH 2 )] through COX. These precursors are used to synthesize numerous prostanoids, including PGE 2 . Prostaglandin E 2 (PGE 2 ) promotes cell proliferation and cell migration and inhibits apoptosis. CYP2S1 metabolism of PGG 2 presumably sequesters PGG 2 and PGH 2 , making them unavailable for synthesis of prostanoids such as PGE 2 . Whether CYP2S1 contributes to prostaglandin metabolism and influences cell physiological remains to be determined. The purpose of this study was to evaluate the physiological role of CYP2S1, if any, in human bronchial epithelial cells [SV40-derived bronchial epithelial cell line (BEAS-2B)]. To do this, we used small interfering RNA to deplete CYP2S1 mRNA and protein by approximately 75% and evaluated the impact of CYP2S1 depletion on cell proliferation and migration. CYP2S1 depletion enhanced both cell proliferation and migration in BEAS-2B cells. Consistent with the proposed role of CYP2S1 in PGE 2 synthesis, the reduction in CYP2S1 expression doubled intracellular PGE 2 levels. Pharmacological administration of PGE 2 enhanced cell proliferation in BEAS-2B cells but failed to promote migration. Our data reveal an important role for CYP2S1 in the regulation of cell proliferation and migration, occurring in part through modulation of prostaglandin synthesis.