Semenogelins Are Ectopically Expressed in Small Cell Lung Carcinoma

Two proteins recovered from cell surface adhesion complexes in a small cell lung carcinoma (SCLC) cell line were identified as fragments of the seminal plasma proteins semenogelin I and semenogelin II. Association of both proteins with the adhesion complexes was induced by epidermal growth factor. Expression of semenogelins was previously thought to be highly specific to seminal vesicles, but Western blot analysis demonstrated that semenogelin II is widely expressed in SCLC cell lines and occasionally in other malignant cell lines. Although semenogelin expression is normally restricted to males, two SCLC cell lines from female patients were also positive for semenogelin II expression. Immunohistochemical analysis demonstrated diffuse expression of semenogelins in 12 of 13 SCLC tumors and focal expression in a minority of lung squamous and adenocarcinomas. Semenogelins were secreted into the medium by cultured SCLC cells, which suggested that these proteins may be useful markers for detecting residual tumor burden or recurrence of SCLC after treatment.