Cyclic 3',5'-AMP causes ADAM1/ADAM2 to rapidly diffuse within the plasma membrane of guinea pig sperm
Hunnicutt,Gary R.; Koppel,Dennis E.; Kwitny,Susanna; Cowan,Ann E.
Biology of Reproduction 79(5): 999-1007
Publication date: 2008
Because sperm cannot synthesize new proteins as they journeyto the egg, they use multiple mechanisms to modify the activityof existing proteins, including changes in the diffusion coefficientof some membrane proteins. Previously, we showed that duringcapacitation the guinea pig heterodimeric membrane protein ADAM1/ADAM2(fertilin) transforms from a stationary state to one of rapiddiffusion within the lipid bilayer. The cause for this biophysicalchange, however, was unknown. In this study we examined whetheran increase in cAMP, such as occurs during capacitation, couldtrigger this change. We incubated guinea pig cauda sperm withthe membrane-permeable cAMP analog dibutyryl cAMP (db-cAMP)and the phosphodiesterase inhibitor papaverine and first testedfor indications of capacitation. We observed hypermotility andacrosome-reaction competence. We then used fluorescence redistributionafter photobleaching (FRAP) to measure the lateral mobilityof ADAM1/ADAM2 after the db-cAMP treatment. We observed thatdb-cAMP caused roughly a 12-fold increase in lateral mobilityof ADAM1/ADAM2, yielding diffusion similar to that observedfor sperm capacitated in vitro. When we repeated the FRAP ontesticular sperm incubated in db-cAMP, we found only a modestincrease in lateral mobility of ADAM1/ADAM2, which underwentlittle redistribution. Interestingly, testicular sperm alsocannot be induced to undergo capacitation. Together, the datasuggest that the release of ADAM1/ADAM2 from its diffusion constraintsresults from a cAMP-induced signaling pathway that, like othersof capacitation, is established during epididymal sperm maturation.