Hypothetical gene C18orf42 encodes a novel protein kinase A-binding protein

The substrate specificity of cAMP-dependent protein kinase A (PKA) is controlled by its interaction with the A-kinase anchoring protein (AKAP) family. Individual AKAP members are localized to particular intracellular sites and tether PKA specifically to the subcellular compartments where target substrates exist. Here, we report that the human hypothetical gene C18orf42 encodes a novel PKA-binding protein that potentially regulates PKA-AKAP interactions. C18orf42 is expressed preferentially in neural tissues. Functional motif searching predicted that C18orf42 may encode a short protein that contains a putative PKA-binding motif. To confirm this possibility, we applied the CRISPR/Cas9 genome-editing system to incorporate the FLAG tag into the C-terminus of the endogenous C18orf42 protein in the mouse neural cell line Neuro2a. Immunoprecipitation and immunoblotting using anti-FLAG antibody showed translation of the endogenous C18orf42 protein and the physical interaction of the C18orf42 protein with PKA subunits. Immunoprecipitation and pull-down assays showed that C18orf42 binds specifically to the type II regulatory subunits of PKA. Unlike the expression of many AKAPs, that of C18orf42 could block the AKAP-mediated subcellular localization of PKA. These findings suggest that C18orf42 may be a novel PKA signaling gene that serves as an endogenous disruptor peptide for PKA-AKAP interactions.