Human sperm plasma membrane progesterone receptor(s) and the acrosome reaction.
Progesterone initiation of te human sperm acrosome reaction (AR) includes stimulation of a transient Ca2+ influx and a transient Cl- efflux. A role for one or more plasma membrane receptors has been suggested, but, except for evidence supporting the involvement of a sperm GABAA-like receptor/Cl- channel, there is little information about possible receptor identity. Here, we attempt to identify plasma membrane progesterone receptors in human sperm using a mouse monoclonal antibody (mAb-C262) raised against the C-terminal steroid-binding domain of the human intracellular progesterone receptor. C-262 inhibited the progesterone-initiated AR in a dose-dependent manner. Maximum inhibition was 77% as detected by fluorescein isothiocyanate (FITC)-concanavalin A (conA). Motility was unaffected. A control mouse mAb (h-151) raised against the human estrogen receptor did not inhibit the progesterone-initiated AR. Western blotting with C-262, but not with h-151, detected a major sperm protein band of 50-52 kDa. In indirect immunofluorescence localization studies, live and ethanol-fixed uncapacitated sperm and fixed capacitated sperm incubated with C-262, but not with h-151, displayed fluorescence at the equatorial segment region of the sperm head plasma membrane. In spectrofluorometric studies using capacitated sperm loaded with the Ca2+ probe Fura-2 or the Cl- probe MEQ, C-262 but not h-151 inhibited both Ca2+ influx and Cl- efflux. These ion fluxes could be due to the binding of progesterone to two different receptor/channels or to its binding to one and cross talk with the other. Our results strongly support the involvement of sperm plasma membrane receptors in the progesterone-initiated AR and provide a candidate for one such receptor.
Sabeur
K
K
Department of Cell Biology and Human Anatomy, University of California School of Medicine, Davis, California 95616-8643, USA.
Edwards
D P
DP
Meizel
S
S
D000177:Acrosome / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001665:Binding Sites; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D008297:Male; D051379:Mice; D011374:Progesterone / Q000494:pharmacology; D011980:Receptors, Progesterone / Q000037:antagonists & inhibitors / Q000276:immunology / Q000502:physiology*; D013075:Sperm Capacitation; D013094:Spermatozoa / Q000378:metabolism / Q000648:ultrastructure*
D000911:Antibodies, Monoclonal; D002712:Chlorides; D011980:Receptors, Progesterone; D011374:Progesterone; D002118:Calcium