Galectin‐3 is a substrate for prostate specific antigen (PSA) in human seminal plasma

Abstract

Background Galectin-3 is a multivalent carbohydrate-binding protein involved in cell adhesion, cell cycle control, immunomodulation, and cancer progression, including prostate cancer. Galectin-3 function is regulated by proteolytic cleavage that destroys galectin-3 multivalency while preserving carbohydrate-binding activity. In human semen, galectin-3 is present in seminal plasma and is also associated with prostasomes, exosome-like vesicles secreted by the prostate. In the current study, we characterized the proteolytic activity that cleaves galectin-3 in human seminal plasma. Methods An in vitro assay was developed to investigate galectin-3 cleavage in seminal plasma. The effect of protease inhibitors, divalent ion chelators, and Zn2+ on the cleavage activity was determined. Proteases enriched from seminal plasma were tested for their ability to cleave galectin-3. Affinity purification and microsequence analysis were used to identify the cleavage site in galectin-3. Results Galectin-3 was identified in human seminal plasma in an intact and truncated form. Gelatinases enriched from seminal plasma did not cleave galectin-3. Inhibitor studies indicated that the galectin-3 cleavage activity in seminal plasma is a Zn2+ sensitive, serine protease. Prostate specific antigen (PSA) was demonstrated to cleave galectin-3 between tyrosine107-glycine108 and produce a functionally-active, monovalent lectin. Conclusions PSA is a chymotrypsin-like serine protease secreted by the prostatic epithelium and normally functions in liquefaction of semen following ejaculation. Furthermore, PSA is implicated in the promotion of localized prostate tumors and bone metastases by its roles in immunomodulation, invasion, and apoptosis. Our results indicate that PSA regulates galectin-3 in human semen and may regulate galectin-3 function during prostate cancer progression.

Alteration of Galectin-3 in Tears of Patients With Dry Eye Disease

“…As with human tears, gelatinolytic activity and MMP9 immunoreactivity have been identified in human seminal plasma, however, endogenous metalloproteases purified from seminal plasma have failed to cleave galectin-3. 40 It is now clear that other proteases, such as prostate specific antigen, MMP13, neutrophil elastase, and leishmanolysin, can also degrade galectin-3. 40-43 Exploring whether these or other candidates are responsible for the proteolytic degradation of galectin-3 at the ocular surface could bring novel insights into the mechanisms of epithelial dysfunction in dry eye disease.…”

Tyrosine-phosphorylated Galectin-3 Protein Is Resistant to Prostate-specific Antigen (PSA) Cleavage

“…Galectin-3 phosphorylated at serine 6 showed reduced binding to laminin and asialomucin and resulted in a diminished ability of galectin-3 to protect cells from cisplatin-induced apoptosis (1). Glycogen synthase kinase ␤ (GSK-3␤) is responsible for phosphorylation of serine 92 and 96, and these phosphorylations are mediated by Axin (29). In our recent study, we demonstrated that galectin-3 could be phosphorylated by c-Abl at Tyr-79, -107, and -118, where Tyr-107 is the major phosphorylation site (2).…”

“…PSA was demonstrated to cleave galectin-3 between Tyr-107 and Gly-108 and produce a functionally active, monovalent lectin (29). Because Tyr-107 is the major phosphorylation site, we checked the ability of active PSA to cleave galectin-3 phosphorylated on Tyr-107.…”

“…Cleavage sites of human galectin-3 by MMPs were identified between Gly-32-Ala-33 and Ala-62-Tyr-63 amino acids resulting in 27-and 22-kDa peptides, respectively (12). Recently, it was shown that galectin-3 can be cleaved by the prostate-specific antigen after Tyr-107, and this cleavage destroys galectin-3 multivalency while preserving its carbohydrate binding activity (29). In solution, galectin-3 largely occurs as a monomer.…”

“…Saraswati et al (29) showed that active prostatespecific antigen (PSA) cleaves galectin-3 between amino acid Tyr-107 and Gly-108.…”