Identification, purification and characterization of a novel human blood protein with binding affinity for prostate secretory protein of 94 amino acids

Abstract

PSP94 (prostate secretory protein of 94 amino acids), an abundant protein within semen, has reported local functions within the reproductive tract and reported systemic functions. Mechanisms of action remain poorly understood, but binding to undefined molecules within the prostate, pituitary, testis and blood may initiate some of these actions. PSP94 serum measurements, especially of bound and free forms, have potential clinical utility in prostate cancer management. Identification of the binding molecules will help in the understanding of PSP94's action, and enable further development of PSP94 serum assays. PSPBP (PSP94-binding protein) was purified from human serum by ammonium sulphate fractionation, ion-exchange and affinity chromatography. The glycosylated protein ran as two bands on SDS/PAGE (70 and 95 kDa). N-terminal sequencing yielded a 30-amino-acid sequence, identical with the translated N-terminal region of a previously published cDNA (GenBank accession number AX136261). Reverse transcriptase PCR and plaque hybridization demonstrated PSPBP mRNA in peripheral blood leucocytes and in a prostate cDNA library. Northern blotting showed 2 kb mRNA species in prostate, testis, ovary and intestine. Immunohistochemistry demonstrated PSPBP in tissues, including pituitary and Leydig cells, supporting a role for PSP94 in hormonal control at the pituitary gonadal axis. ELISA demonstrated that PSPBP levels were significantly lower (P=0.0014) in the serum of a prostate cancer population (n=65) compared with a control population (n=70). PSPBP identification will help the understanding of PSP94's functions and facilitate ELISA development to address the clinical value of PSP94 serum assays.

Growth inhibition properties of the putative prostate cancer biomarkers PSP94 and CRISP-3

“…18 In human blood, however, CRISP-3 is known to bind to the human plasma protein AIBG, 19 whereas PSP94 is complexed to CRISP-9. 20 It seems likely that the increased CRISP-3 and decreased PSP94 levels in PCa have considerable effects on the ratio of the distinct PSP94 complexes.…”

β-Microseminoprotein binds CRISP-3 in human seminal plasma

“…A novel protein with an N-terminal SCP domain has been identified in human blood plasma and is called PSP94-binding protein (PSPBP) as it binds to β -microseminoprotein (MSP), also known as prostate secretory protein of 94 amino acids (PSP94) [6]. MSP is one of the three predominant proteins secreted by the prostate gland, but it is also present in other body fluids, e.g., tracheobronchial fluid.…”

“…Recently, the crystal structure of a snake venom CRISP was elucidated [5]. This confirmed the previously proposed two-domain structure of CRISPs with a large N-terminal SCP domain (after sperm coating protein, an alternative name for murine CRISP-1) and a smaller, compact C-terminal domain, separated by a hinge-region [3,5].A novel protein with an N-terminal SCP domain has been identified in human blood plasma and is called PSP94-binding protein (PSPBP) as it binds to β -microseminoprotein (MSP), also known as prostate secretory protein of 94 amino acids (PSP94) [6]. MSP is one of the three predominant proteins secreted by the prostate gland, but it is also present in other body fluids, e.g., tracheobronchial fluid.…”

“…MSP is one of the three predominant proteins secreted by the prostate gland, but it is also present in other body fluids, e.g., tracheobronchial fluid. In general, MSP-synthesis is associated with tissue producing [7,8].It is yet unknown whether MSP binds to PSPBP through the SCP domain or via the large C-terminal part of the molecule [6]. One way to answer this question is to investigate whether MSP binds other proteins with an SCP domain, and the abundance of both MSP and CRISP-3 in human seminal plasma prompted us to test the hypothesis that these proteins form high-affinity complexes.…”

“…Although both MSP and CRISP-3 also are present in blood plasma, we did not detect MSP-CRISP-3 complexes in this fluid. This is probably due to the much lower concentration of MSP (5-20 μg/L) compared to CRISP-3 (2-10 mg/L) and the fact that each protein has another more suitable binding partner in blood [6,10].In prostate cancer, expression of MSP often decreases with higher tumor grade [19,20], whereas expression of CRISP-3 follows the reverse pattern with high expression in high-grade tumors [21,22], unpublished observations. A recent report showing that MSP reduces tumor growth in a prostate cancer rat model [23] suggests that the acquired imbalance in MSP-CRISP-3 expression may play a role in the pathophysiology of human prostate cancer.…”