Mediates cAMP-dependent signaling triggered by receptor binding to GPCRs. PKA activation regulates diverse cellular processes such as cell proliferation, the cell cycle, differentiation and regulation of microtubule dynamics, chromatin condensation and decondensation, nuclear envelope disassembly and reassembly, as well as regulation of intracellular transport mechanisms and ion flux (PubMed:9368018). Regulates the abundance of compartmentalized pools of its regulatory subunits through phosphorylation of PJA2 which binds and ubiquitinates these subunits, leading to their subsequent proteolysis. Phosphorylates GPKOW which regulates its ability to bind RNA (By similarity). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by cAMP. A number of inactive tetrameric holoenzymes are produced by the combination of homo- or heterodimers of the different regulatory subunits associated with two catalytic subunits. cAMP causes the dissociation of the inactive holoenzyme into a dimer of regulatory subunits bound to four cAMP and two free monomeric catalytic subunits. Interacts with PRKAR1A and PRKAR2B (By similarity). The cAMP-dependent protein kinase catalytic subunit binds PJA2. Interacts with GPKOW. Translocates into the nucleus (monomeric catalytic subunit). The inactive holoenzyme is found in the cytoplasm. Isoform 1 is found in all tissues examined, with the highest expression in the brain and very low levels in the testis. Isoform 2 is strongly expressed in the brain, in the prelimbic and insular cortex. Isoform 3 is also found only in the brain, but at very low levels. Asn-3 is deaminated to Asp in more than 25% of the proteins, giving rise to 2 major isoelectric variants, called CB and CA respectively (0.4 pH unit change). Deamidation proceeds via the so-called beta-aspartyl shift mechanism and yields either 'D-Asp-2' (major) or 'D-isoAsp-2' (minor), in addition to L-isomers. Deamidation occurs after the addition of myristate. The Asn-3 form reaches a significantly larger nuclear/cytoplasmic ratio than the 'Asp-2' form (By similarity). Belongs to the protein kinase superfamily. AGC Ser/Thr protein kinase family. cAMP subfamily.