Pe. Visconti et al., CAPACITATION OF MOUSE SPERMATOZOA .2. PROTEIN-TYROSINE PHOSPHORYLATION AND CAPACITATION ARE REGULATED BY A CAMP-DEPENDENT PATHWAY, Development, 121(4), 1995, pp. 1139-1150
In the accompanying report (Visconti, P.E., Bailey, J.L., Moore, G.D.,
Pan, D., Olds-Clarke, P. and Kopf, G.S. (1995) Development, 121, 1129
-1137) we demonstrated that the tyrosine phosphorylation of a subset o
f mouse sperm proteins of M(r) 40,000-120,000 was correlated with the
capacitation state of the sperm. The mechanism by which protein tyrosi
ne phosphorylation is regulated in sperm during this process is the su
bject of this report. Cauda epididymal sperm, when incubated in media
devoid of NaHCO3, CaCl2 or bovine serum albumin do not display the cap
acitation-associated increases in protein tyrosine phosphorylation of
this subset of proteins. This NaHCO3, CaCl2 or bovine serum albumin re
quirement for protein tyrosine phosphorylation can be completely overc
ome by the addition of biologically active, but not inactive, cAMP ana
logues. Addition of the active cAMP analogues to sperm incubated in me
dia devoid of NaHCO3, CaCl2 or bovine serum albumin overcomes the inab
ility of these media to support capacitation, as assessed by the abili
ty of the cells to acquire the pattern B chlortetracycline fluorescenc
e, to undergo the zona pellucida-induced acrosome reaction and, in som
e cases, to fertilize metaphase II-arrested eggs in vitro. The effects
of the cAMP analogues to enhance protein tyrosine phosphorylation and
to promote capacitation appears to be at the level of the cAMP-depend
ent protein kinase (PKA), since two specific inhibitors of this enzyme
(H-89 and RP-cAMPS) block the capacitation-dependent increases in pro
tein tyrosine phosphorylation in sperm incubated in media supporting c
apacitation. Capacitation, as assessed by the aforementioned endpoints
, also appears to be inhibited by H-89 in a concentration-dependent ma
nner. These results provide further evidence for the interrelationship
between protein tyrosine phosphorylation and the appearance of the ca
pacitated state in mouse sperm. They also demonstrate that both protei
n tyrosine phosphorylation and capacitation appear to be regulated by
cAMP/PKA. Up-regulation of protein tyrosine phosphorylation by cAMP/PK
A in sperm is, to our knowledge, the first demonstration of such an in
terrelationship between tyrosine kinase/phosphatase and PKA signaling
pathways.