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Co‐purification of Mac‐2 binding protein with galectin‐3 and association with prostasomes in human semen
Author(s) -
Block Ashley S.,
Saraswati Sarika,
Lichti Cheryl F.,
Mahadevan Maha,
Diekman Alan B.
Publication year - 2010
Publication title -
the prostate
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.295
H-Index - 123
eISSN - 1097-0045
pISSN - 0270-4137
DOI - 10.1002/pros.21287
Subject(s) - semen , glycoprotein , prostate , sperm , chemistry , cancer research , biology , biochemistry , medicine , cancer , genetics , botany
BACKGROUND Prostasomes are exosome‐like vesicles that are secreted by the prostate and incorporated into semen during ejaculation. Human prostasomes are proposed to function in regulation of sperm function, immunosuppression, and prostate cancer progression. Previously, we identified galectin‐3 on the surface of prostasomes. Galectin‐3 is a β‐galactoside binding protein involved in immunomodulation, cell interactions, and cancer progression, including prostate cancer. Functional characterization of galectin‐3 in a given biological environment includes identification of its target glycoprotein ligands. METHODS Candidate galectin‐3 ligands in prostasomes were identified by tandem mass spectrometry of proteins that co‐purified with galectin‐3 during lactose affinity chromatography. Immunochemical and biochemical methods were used to investigate the association of Mac‐2 binding protein (M2BP) with prostasomes. RESULTS Proteins identified by tandem mass spectrometry included M2BP, CD26/dipeptidyl peptidase IV, prolactin‐inducible protein (PIP), olfactomedin‐4 (OLFM4), and semenogelins I and II (SgI and SgII). M2BP is a known galectin‐3 ligand that was not previously described in prostasomes. M2BP protein bands were detected in the testis, epididymis, vas deferens, prostate, seminal vesicle, and sperm extracts. In seminal plasma, M2BP was identified in the soluble fraction and in purified prostasomes. Surface biotinylation and immunofluorescence studies indicated that M2BP is present on the prostasome surface and on sperm, respectively. CONCLUSIONS M2BP, CD26, PIP, OLFM4, and SgI and SgII are candidate glycoprotein ligands for galectin‐3 in prostasomes. Given their overlap in functional significance with prostasomes and galectin‐3, the identification of these glycoproteins as galectin‐3 ligands in prostasomes lays the groundwork for future studies of prostasomes in reproduction and prostate cancer. Prostate 71:711–721, 2011. © 2010 Wiley‐Liss, Inc.