Protein kinases are enzymes important for signal transduction in the regulation of cellular processes. The cAMP-dependent protein kinase A (PKA) has been previously reported to regulate the activity of the Src family kinase Fyn, an event important for cellular migration. This study aimed to characterize the reciprocal interaction, in which Fyn regulates PKA. In addition to our preliminary, unpublished findings that Fyn phosphorylates the PKA catalytic subunit at Y69 to increase its catalytic activity, we have shown through co-immunoprecipitation that Fyn physically associates with PKA in HEK293 cells. Quantitative mass spectrometry and subsequent biochemical validation shows that PKACα undergoes enhanced binding to a complex of centrosomal and Golgi-localized A-kinase anchoring proteins when Fyn is overexpressed, independent of Fyn kinase activity. Fyn was found in this complex, as well, implicating its involvement as an adaptor protein. Co-immunoprecipitation experiments with various Fyn alleles demonstrated the dispensability of the Fyn SH3 domain and the functioning SH2 domain in binding to PKACα. GST-fusion proteins containing either of these domains were also unable to enrich PKACα from HEK293 lysates. Fyn was found to bind PKACα independent of its association with the regulatory subunit, and preliminary data suggests that this interaction is direct through purified protein pulldown experiments. We hypothesize that this regulatory interaction activates PKA at the centrosome and Golgi apparatus, facilitating the potential phosphorylation of proximal substrates involved in cytoskeletal organization and mitotic processes
