Dissociation between AKAP3 and PKARII Promotes AKAP3 Degradation in Sperm Capacitation

Abstract

Ejaculated spermatozoa must undergo a series of biochemical modifications called capacitation, prior to fertilization. Protein-kinase A (PKA) mediates sperm capacitation, although its regulation is not fully understood. Sperm contain several A-kinase anchoring proteins (AKAPs), which are scaffold proteins that anchor PKA. In this study, we show that AKAP3 is degraded in bovine sperm incubated under capacitation conditions. The degradation rate is variable in sperm from different bulls and is correlated with the capacitation ability. The degradation of AKAP3 was significantly inhibited by MG-132, a proteasome inhibitor, indicating that AKAP3 degradation occurs via the proteasomal machinery. Treatment with Ca2+-ionophore induced further degradation of AKAP3; however, this effect was found to be enhanced in the absence of Ca2+ in the medium or when intracellular Ca2+ was chelated the degradation rate of AKAP3 was significantly enhanced when intracellular space was alkalized using NH4Cl, or when sperm were treated with Ht31, a peptide that contains the PKA-binding domain of AKAPs. Moreover, inhibition of PKA activity by H89, or its activation using 8Br-cAMP, increased AKAP3 degradation rate. This apparent contradiction could be explained by assuming that binding of PKA to AKAP3 protects AKAP3 from degradation. We conclude that AKAP3 degradation is regulated by intracellular alkalization and PKARII anchoring during sperm capacitation.

Central role of soluble adenylyl cyclase and cAMP in sperm physiology

“…This peptide has been first used to study PKA signaling in sperm 119,133 , and later expanded to other cell types. The stearated peptide HT31 impairs sperm motility and the onset of signaling pathways associated with sperm capacitation 47,119,134 . Interestingly, this blocking peptide produced a stronger inhibition of motility that obtained solely with the use of PKA inhibitors such as H89.…”

Testis‐specific calcium‐binding protein CBP86‐IV (CABYR) binds with phosphoglycerate kinase 2 in vitro and in vivo experiment

“…Beginning with calcium activation and modulation, AKAPs played an important rule on the complex formation with different signal molecules (Xu & Qi, ). Meanwhile, the regulation of protein complex is supposed to be coupled with the degradation of AKAP3 by intracellular alkalisation and PKARII anchoring during sperm capacitation (Hillman, Ickowicz, Vizel, & Breitbart, ), which also indicated the potential interaction with CABYR. PGK2 was responsible for the ATP supply according to received cell signals and ensures the correct assembly of fibrous sheath of mammalian sperm flagella including the important structural protein Ropporin.…”

Differential expression of TLRs and AKAP3 in cigarette smoked mice testis

“…AKAP3, family of AKAP, is localised in bovine spermatozoa (Bajpai et al, ) and for a long time, and it was suggested to be a sperm‐specific protein (Vijayaraghavan et al, ). During sperm capacitation, degradation of AKAP3 is regulated by intracellular alkalization and PKARII anchoring (Hillman, Ickowicz, Vizel, & Breitbart, ). The AKAP3 degradation plays a role in sperm capacitation process and the degree to which is regulated by AKAP3 tyrosine phosphorylation levels (Vizel, Hillman, Ickowicz, & Breitbart, ).…”