Study of human PRKAR1A and its role in autophagy

The human PRKAR1A gene is a 381- amino acid protein encoding the regulatory subunit (RIα) of the cAMP dependent Protein Kinase A (PKA). The main function of PRKAR1A is to regulate the catalytic activity of PKA. PRKAR1A is shown to regulate autophagy via association with mTOR kinase and colocalization with the autophagy marker proteins LC3B, Rab7 and Rab9. Contradictory findings regarding the localization and function of the protein in autophagy have been reported. The main aim of this study was to investigate a functional role of the protein in relation to autophagy. Our in vitro and in vivo assays show that PRKAR1A interacts with the ATG8 family proteins, and strongest with GABARAPL2. PRKAR1A exhibits mainly diffuse cytosolic localization in the cells, and did not show a significant colocalization with LC3B, GABARAP or the autophagy receptor p62. Interestingly, colocalization of PRKAR1A with GABARAP was enhanced by the presence of the catalytic subunit of PKA. Furthermore, PRKAR1A was degraded by the proteasomal system and not by autophagy. However, PRKAR1A was involved in the regulation of autophagy as observed by a reduction in the average number of LC3B puncta in cells expressing EGFP-PRKAR1A upon starvation. It is still unclear if PRKAR1A directly regulates autophagy or has an indirect function. The strongest binding to GABARAP family members could suggest this protein might have a role during autophagosome maturation. However, further studies are crucial to identify the role of PRKAR1A in autophagy