Hl. Galantinohomer et al., REGULATION OF PROTEIN-TYROSINE PHOSPHORYLATION DURING BOVINE SPERM CAPACITATION BY A CYCLIC ADENOSINE 3',5'-MONOPHOSPHATE-DEPENDENT PATHWAY, Biology of reproduction, 56(3), 1997, pp. 707-719
Mammalian sperm capacitation, defined as an obligatory maturational pr
ocess leading to the development of the fertilization-competent state,
results from a poorly understood series of morphological and molecula
r events. We report here that ejaculated bovine sperm, incubated under
conditions that support capacitation in vitro, display a reproducible
pattern of protein tyrosine phosphorylations that are regulated by a
cAMP-dependent pathway. The appearance of these tyrosine phosphorylate
d proteins correlated temporally with the time course of capacitation
induced by heparin, and these phosphorylations displayed a similar hep
arin concentration dependence. Glucose, which inhibits capacitation, i
nhibited these protein tyrosine phosphorylations in media containing h
eparin. The biologically active cAMP analogues (dibutyryl cAMP [db-cAM
P], 8-bromo cAMP, Sp-cAMPS) and the phosphodiesterase inhibitor 3-isob
utyl-1-methylxanthine (IBMX) induced the same protein tyrosine phospho
rylation patterns as seen with heparin. Moreover, these cAMP agonists
could overcome the inhibition of the heparin-induced tyrosine phosphor
ylations by glucose. In contrast, Rp-adenosine-3',5'-cyclic monophosph
orothioate (Rp-cAMPS), a protein kinase A (PK-A) antagonist, blocked t
he capacitation-associated increases in protein tyrosine phosphorylati
on. This cAMP regulation of the protein tyrosine phosphorylation patte
rn is mediated by PK-A since o)ethyl]-5-isoquinolinesulfonamide-dehydr
ochloride (H89), another inhibitor of PK-A, inhibited the heparin-indu
ced protein tyrosine phosphorylation pattern in a concentration-depend
ent manner in either the absence or presence of db-cAMP, IBMX, and glu
cose. These data support a model for sperm capacitation that includes
protein tyrosine phosphorylation as an important regulatory pathway, a
nd a role for cAMP/PK-A in the regulation of this pathway leading to c
apacitation. These studies are the first to report a unique interrelat
ionship between tyrosine kinase/ phosphatase and cAMP signaling pathwa
ys at the level of PK-A in bovine sperm capacitation.