PKA, PKC, and AKAP localization in and around the neuromuscular junction
1 Department of Neurosciences and the National Center for Microscopy and Imaging Research, University of California, San Diego, La Jolla, CA 92093-0608, USA
2 Howard Hughes Medical Institute, Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093-0654, USA
3 University of Texas, MD Anderson Cancer Center, Dept. of Genitourinary Medical Oncology Box 427, 1515 Holcombe Blvd., Houston, TX 77030-4009, USA
4 Department of Pharmacology, University of California, San Diego, La Jolla, CA 92093-0640, USA
5 Howard Hughes Medical Institute, Vollum Institute, Portland, OR 97201-3098, USA
BMC Neuroscience 2001, 2:17 doi:10.1186/1471-2202-2-17Published: 23 October 2001
One mechanism that directs the action of the second messengers, cAMP and diacylglycerol, is the compartmentalization of protein kinase A (PKA) and protein kinase C (PKC). A-kinase anchoring proteins (AKAPs) can recruit both enzymes to specific subcellular locations via interactions with the various isoforms of each family of kinases. We found previously that a new class of AKAPs, dual-specific AKAPs, denoted D-AKAP1 and D-AKAP2, bind to RIα in addition to the RII subunits.
Immunohistochemistry and confocal microscopy were used here to determine that D-AKAP1 colocalizes with RIα at the postsynaptic membrane of the vertebrate neuromuscular junction (NMJ) and the adjacent muscle, but not in the presynaptic region. The labeling pattern for RIα and D-AKAP1 overlapped with mitochondrial staining in the muscle fibers, consistent with our previous work showing D-AKAP1 association with mitochondria in cultured cells. The immunoreactivity of D-AKAP2 was distinct from that of D-AKAP1. We also report here that even though the PKA type II subunits (RIIα and RIIβ) are localized at the NMJ, their patterns are distinctive and differ from the other R and D-AKAP patterns examined. PKCβ appeared to colocalize with the AKAP, gravin, at the postsynaptic membrane.
The kinases and AKAPs investigated have distinct patterns of colocalization, which suggest a complex arrangement of signaling micro-environments. Because the labeling patterns for RIα and D-AKAP 1 are similar in the muscle fibers and at the postsynaptic membrane, it may be that this AKAP anchors RIα in these regions. Likewise, gravin may be an anchor of PKCβ at the NMJ.