Transmembrane Signaling Regulates the Remodeling of the Actin Cytoskeleton:Roles of PKC and Adducin

Abstract

We tested the hypothesis that Pkc53E regulates adducin to orchestrate the remodeling of the membrane skeleton following the transmembrane GPCR-Gq signaling. Adducin is a known substrate of PKC and is critical for the assembly of the membrane skeleton by cross-linking actin filaments with the spectrin network. In Drosophila photoreceptors, loss of function in pkc53E leads to retinal degeneration while Pkc53E-RNAi negatively impacts the actin cytoskeleton of the visual organelle rhabdomeres. Unexpectedly, Pkc53E-RNAi enhances the degeneration caused by the loss of PLC{beta}4 (norpAP24). We show that when PLC{beta}4 is absent Plc21C may be activated instead for activating Pkc53E. We investigate whether Pkc53E phosphorylates adducin in vivo and observed that levels of phosphorylated adducin at the conserved PKC site were greatly reduced in a null allele of pkc53E. We show Pkc53E-RNAi did not modify adducin-RNAi, which exerts a more severe effect on the actin cytoskeleton. Moreover, overexpression of the mCherry-tagged adducin that appears to act in a dominant-negative manner interferes with the spectrin interaction leading to the apical expansion of rhabdomeres similar to that of {beta}-spectrin-RNAi. We performed epistasis analysis and show that double mutants of the tagged adducin and Pkc53E-RNAi display the expansion phenotype at the eclosion, but progress to severe degeneration in adult photoreceptors. Together, most of our findings support that adducin is likely regulated by Pkc53E in Drosophila photoreceptors.