The Ovarian-Carcinoma-Associated Sebaceous Gland Antigen Is a Member of the HMFG2-Positive Family of Epithelial Mucins

Abstract

The ovarian-carcinoma-associated sebaceous gland antigen (SGA) defined by the OM-1 monoclonal antibody (McAb) is a highly glycosylated protein of molecular weight approximately 360 kilodaltons. The HMFG1 and HMFG2 McAbs also detect highly glycosylated high-molecular-weight glycoproteins synthesized by a wide variety of human epithelia. Comparison of the distributions of expression of SGA and the molecules detected by the HMFG1 and HMFG2 McAbs showed that SGA was expressed by a strict subset of HMFG1- and HMFG2-positive cells. The relationship of SGA to HMFG1- and HMFG2-positive molecules was subsequently examined at the molecular level. Analysis of immunoprecipitates from biosynthetically labelled ovarian carcinoma cell lines indicated that HMFG1 and HMFG2 reacted with molecules indistinguishable by this method from SGA. Western blot analysis of proteins present in human milk fat globule membrane preparations showed that SGA was present in these preparations together with protein components reactive with the HMFG1 and HMFG2 antibodies. Western blot analysis, probing for the OM-1-reactive determinant, on proteins specifically immunoprecipitated from ovarian cell lysates by the three antibodies conclusively proved that SGA carries the HMFG2 antigenic determinant. Conversely, SGA does not react with the HMFG1 antibody. These results demonstrate the existence in human epithelia of more than one HMFG2-positive molecule. SGA is therefore one of at least two independently expressed HMFG-2-positive human epithelial mucins.