Cyclophilin A is not acetylated at Lysine-82 and Lysine-125 in resting and stimulated platelets

Cyclophilin A (CyPA), a member of the family of cyclophilins, is widely expressed by all prokaryotic and eukaryotic cells. Upon activation, CyPA can also be released from platelets, and engages in extracellular functions via interaction with the CD147 receptor that contribute to cardiovascular disease. CyPA was recently found to be acetylated at K82 and K125, two lysines conserved in most species, and these modifications were required for secretion of acetylated CyPA in response to cell activation in vascular smooth muscle cells. We here addressed whether acetylation at these sitesis also required for release of acetylated CyPA from platelets. Western blot analyses demonstrated the presence of CyPA in human and mouse platelets. Thrombin-stimulation resulted in CyPA release from platelets, however, no acetylation was observed –neither in cell lysates nor in supernatants of untreatedand thrombin-activated platelets. Similar results were obtained after immunoprecipitation of CyPA from platelets. In vitro acetylation of recombinant humanCyPA by p300 acetyltransferase likewise did not induce CyPA acetylation. Using shotgun proteomics we detected two CyPA peptide precursors in the recombinant protein, acetylatedat K28, but again no acetylation was found in CyPA from resting or stimulated platelet samples. Our findings suggest that acetylation of CyPA is not a major protein modification in platelets, and that CyPA acetylation at K82 and K125 is not required for its secretion from platelets.