Mutation Associated with Aggressive Tumors PRKAR1A Protein Kinase A Effects of an Expressed

Most PRKAR1A tumorigenic mutations lead to nonsense mRNA that is decayed; tumor formation has been associated with an increase in type II protein kinase A (PKA) subunits. The IVS6+1G>T PRKAR1A mutation leads to a protein lacking exon 6 sequences [R1A#184-236 (R1A#6)]. We compared in vitro R1A#6 with wild-type (wt) R1A. We assessed PKA activity and subunit expression, phosphorylation of target molecules, and properties of wt-R1A and mutant (mt) R1A; we observed by confocal microscopy R1A tagged with green fluorescent protein and its interactions with Cerulean-tagged catalytic subunit (CA). Introduction of the R1A#6 led to aberrant cellular morphology and higher PKA activity but no increase in type II PKA subunits. There was diffuse, cytoplasmic localization of R1A protein in wt-R1A– and R1A#6-transfected cells but the former also exhibited discrete aggregates of R1A that bound CA; these were absent in R1A#6-transfected cells and did not bind CA at baseline or in response to cyclic AMP. Other changes induced by R1A#6 included decreased nuclear CA. We conclude that R1A#6 leads to increased PKA activity through the mt-R1A decreased binding to CA and does not involve changes in other PKA subunits, suggesting that a switch to type II PKA activity is not necessary for increased kinase activity or tumorigenesis. [Cancer Res 2008;68(9):3133–41]