PROTEIN-KINASE A-ANCHORING INHIBITOR PEPTIDES ARREST MAMMALIAN SPERM MOTILITY

Cyclic AMP-dependent protein kinase (PKA) is anchored at specific subc ellular sites through the interaction of the regulatory subunit (R) wi th protein kinase A-anchoring proteins (AKAPs) via an amphipathic heli x binding motif, Synthetic peptides containing this amphipathic helix domain competitively disrupt PKA binding to AKAPs and cause a loss of PKA modulation of cellular responses, In this report we use S-Ht31, a cell-permeant anchoring inhibitor peptide, to study the role of PKA an choring in sperm, Our analysis of three species of mammalian sperm det ected three isoforms of PKA (RII alpha, RII beta, and RI beta) and one 110-kDa AKAP, The addition of S-Ht31 to bovine caudal epididymal sper m inhibits motility in a time- and concentration dependent manner, A c ontrol peptide, S-Ht31-P, identical to S-Ht31 except for a proline for isoleucine substitution to prevent amphipathic helix formation, had n o effect on motility, The inhibition of motility by S-Ht31 is reversib le but only if calcium is present in the suspension buffer, suggesting a role for PKA anchoring in regulating cellular calcium homeostasis. Surprisingly, inhibition of PKA catalytic activity had little effect o n basal motility or motility stimulated by agents previously thought t o work via PKA activation, These data suggest that the interaction of the regulatory subunit of PKA with sperm AKAPs, independent of PKA cat alytic activity, is a key regulator of sperm motility and that disrupt ion of this interaction using cell permeable anchoring inhibitor pepti des may form the basis of a sperm targeted contraceptive.