Galectin-3 is a substrate for prostate specific antigen (PSA) in human seminal plasma.
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 Zn(2+) 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 Zn(2+) 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.
Saraswati
Sarika
S
Department of Biochemistry and Molecular Biology, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA.
Block
Ashley S
AS
Davidson
Mari K
MK
Rank
Roger G
RG
Mahadevan
Maha
M
Diekman
Alan B
AB
D000818:Animals; D002614:Chelating Agents / Q000494:pharmacology; D005260:Female; D037502:Galectin 3 / Q000378:metabolism*; D006168:Guinea Pigs; D006801:Humans; D015151:Immunoblotting; D008297:Male; D017430:Prostate-Specific Antigen / Q000378:metabolism*; D011480:Protease Inhibitors / Q000494:pharmacology; D012661:Semen / Q000378:metabolism*; D020539:Sequence Analysis, Protein; D015032:Zinc / Q000494:pharmacology
D002614:Chelating Agents; D037502:Galectin 3; D011480:Protease Inhibitors; D017430:Prostate-Specific Antigen; D015032:Zinc