Analysis of CA125 antigen in normal human seminal plasma highlights the molecular heterogeneity of underlying glycosylated species

Cancer antigen CA125 represents an extracellular part of transmembrane mucin MUC16 and may be expressed in tissues of the male reproductive tract. It reaches human seminal plasma (hSP) after undergoing the main processes involved in protein speciation: synthesis, posttranslational modifications, compartmentalization, and auto/proteolytic degradation. This study was aimed at profiling CA125-immunoreactive species in hSP from healthy subjects as a specific and unexplored source of this tumor-associated antigen expressed under normal physiological conditions. High molecular mass components from total hSP and corresponding acid-soluble hSP preparations were analyzed. The results indicated that antibodies recognizing two distinct immunogenic areas of CA125 antigen exhibited a common pattern of immunoreactive bands affected by low pH and reducing agents. They comprise a large, heavily glycosylated moiety and a mixture of low glycosylated species ranging from 100 to 150 kDa. High molecular mass CA125-immunoreactive smears overlapped core 2 O-glycans and the Lex glycotope, the latter also being abundant on distinct lower molecular mass immunoreactive bands. Within the bulk of normal hSP mucins, the CA125 antigen is present in low amounts and resides on heterogeneously glycosylated species that may be proteolysis-derived and sensitive to redox environments. Both factors influence the composition of hSP and therefore might affect speciation of mucin16 under normal and pathological conditions.