title: Mechanisms underlying the inhibition of murine sperm capacitation by the seminal protein, SPINKL.
abstract: SPINKL, a serine protease inhibitor kazal-type-like protein initially found in mouse seminal vesicle secretions, possesses structurally conserved six-cysteine residues of the kazal-type serine protease inhibitor family. However, it has no inhibitory activity against serine proteases. Previously, it was found to have the ability to suppress murine sperm capacitation in vitro. Herein, we investigated the mechanisms underlying the suppressive effect of SPINKL on sperm capacitation. Three in vitro capacitation-enhancing agents, including bovine serum albumin (BSA), methyl-beta-cyclodextrin (MBCD), and dibutyryl cyclic AMP (dbcAMP), coupled with 3-isobutyl-1-methylxanthine (IBMX), were used to evaluate the influence of SPINKL on capacitation signaling. Preincubation of sperm with SPINKL suppressed BSA- and MBCD-induced sperm capacitation by blocking three upstream signals of capacitation that is the cholesterol efflux from sperm plasma membranes, extracellular calcium ion influx into sperm, and increases in intracellular cAMP. Moreover, SPINKL also inhibited downstream signal transduction of capacitation since it suppressed dbcAMP/IBMX and N(6) -phenyl cAMP (6-Phe-cAMP)-activated cAMP-dependent protein kinase-associated protein tyrosine phosphorylation. Such inhibition is probably mediated by attenuation of SRC tyrosine kinase activity. Furthermore, SPINKL could not reverse capacitation once sperm had been capacitated by capacitation-enhancing agents or capacitated in vivo in the oviduct. SPINKL bound to sperm existed in the uterus but had disappeared from sperm in the oviduct during the sperm's transit through the female reproductive tract. Therefore, SPINKL may serve as an uncapacitation factor in the uterus to prevent sperm from precocious capacitation and the subsequent acrosome reaction and thus preserve the fertilization ability of sperm.
authors.affiliation: Department of Medical Research, Mackay Memorial Hospital, Tamshui, New Taipei City, Taiwan.
authors.forename: Huan-Chin
authors.initials: HC
authors.lastname: Tseng
authors.forename: Robert Kuo-Kuang
authors.initials: RK
authors.lastname: Lee
authors.forename: Yuh-Ming
authors.initials: YM
authors.lastname: Hwu
authors.forename: Chung-Hao
authors.initials: CH
authors.lastname: Lu
authors.forename: Ming-Huei
authors.initials: MH
authors.lastname: Lin
authors.forename: Sheng-Hsiang
authors.initials: SH
authors.lastname: Li
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D020101:Acrosome Reaction / Q000187:drug effects; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D005260:Female; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D010057:Oviducts / Q000378:metabolism; D010766:Phosphorylation; D053491:Proteinase Inhibitory Proteins, Secretory / Q000378:metabolism* / Q000494:pharmacology; D012710:Serum Albumin, Bovine / Q000494:pharmacology; D013075:Sperm Capacitation / Q000187:drug effects*; D013094:Spermatozoa / Q000187:drug effects / Q000378:metabolism*; D047392:beta-Cyclodextrins / Q000494:pharmacology
chemical_list: D053491:Proteinase Inhibitory Proteins, Secretory; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; C533878:serine protease inhibitor Kazal-type-like protein, mouse; D012710:Serum Albumin, Bovine; D003994:Bucladesine; D002784:Cholesterol; D000242:Cyclic AMP; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine