Beta-microseminoprotein (PSP94), also known as prostate secretory protein 94-amino acid, is a major component of semen. PSP94 is synthesized by the prostate epithelium; however, the protein can also be detected in non-reproductive organs such as in the respiratory and gastrointestinal tracts. A number of functions have been postulated or demonstrated for PSP94, including a modulator of circulating FSH (follicle-stimulating hormone) levels, a motility inhibitor of sperm, a binder of immunoglobulins in the female reproductive tract, a growth regulator and inducer of apoptosis in prostate cancer cells, and a regulator of calcium levels during hypercalcaemia of malignancy. There have been several reports suggesting the existence of cell-surface-binding sites for PSP94 in prostate, pituitary and testis. Several studies have demonstrated a progressive decrease in PSP94 expression as prostate cancer progresses from a hormone-dependent to a hormone-independent state with complete lack of PSP94 production in highly advanced metastatic prostate cancer. Measurement of circulating PSP94 is somewhat confounded by the existence of a PSP binding protein and circulation of both the free and bound forms of the molecule. It is likely that the measurement of total PSP94 is of greater clinical significance than the free form alone.
Swiss-Prot Accession Number: P08118