TIS10/PGS-2 encodes a prostaglandin synthase (PGS) distinct from the previously described enzyme PGS-1 (EC 1.14.99.1). We have now generated antipeptide antisera, directed to an amino acid sequence unique to the murine TIS10/PGS-2 protein, which specifically recognize the TIS10/PGS-2 antigen. TIS10/PGS-2 protein was undetectable in quiescent Swiss 3T3 cells. The level of TIS10/PGS-2 protein peaked between 6 and 8 h following phorbol ester stimulation of cells, then declined to basal levels after 18-24 h. Synthesis of TIS10/PGS-2 protein was dramatically increased in the second hour following mitogen stimulation and remained elevated for several hours. The half-life of the TIS10/PGS-2 protein was 4 h. Immunofluorescence studies demonstrated a perinuclear and cytoplasmic localization of the TIS10/PGS-2 antigen. As expected, detection of induced TIS10/PGS-2 antigen was dependent on protein synthesis. Metabolically labeled TIS10/PGS-2 protein migrated as a 71/73-kDa doublet following immunoprecipitation. Dexamethasone blocked both the TPA- and serum-induced appearance of TIS10/PGS-2 antigen. These studies demonstrate the existence of a mitogen-inducible, glucocorticoid-inhibitable, immunologically distinct prostaglandin synthase protein.