Cloning and Characterization of a Novel A-kinase Anchoring Protein

Compartmentalization of the type II cyclic AMP-dependent kinase (PKA) is achieved through association of the regulatory subunit (RII) with A-kinase anchoring proteins (AKAPs). Using an interaction cloning strategy with RIIalpha as a probe, we have isolated cDNAs encoding a novel 1129-amino acid protein that contains both a PKA binding region and a peroxisome targeting motif. Northern analysis detected mRNAs of 9.7 and 7.3 kb in several rat tissues with the highest levels present in the brain and testis. Western analysis and RII overlay experiments showed that the protein is approximately 220 kDa and was, therefore, named AKAP 220. Immunoprecipitation of AKAP 220 from rat testis extracts resulted in co-purification of the type II PKA holoenzyme. The specific activity of PKA increased 458-fold from 7.2 pmol/min/mg in the cell lysate to 3.3 nmol/min/mg in the immunoprecipitate. Immunohistochemical analysis of rat testicular TM4 cells showed that AKAP 220 and a proportion of RII were co-localized in microbodies that appear to be a subset of peroxisomes. Collectively, these results suggest that AKAP 220 may play a role in targeting type II PKA for cAMP-responsive peroxisomal events.