Interaction of a Novel Chaperone PhLP2A With the Heat Shock Protein Hsp90.

PhLP2 is a small cytosolic protein that belongs to the highly conserved phosducin-like family of proteins. In amniote genomes there are two PhLP2 homologs, PhLP2A and PhLP2B. It has been shown that mammalian PhLP2A modulates the CCT/TRiC chaperonin activity during folding of cytoskeletal proteins. In order to better understand the function of PhLP2A in cellular protein quality control system, in the present study we have searched for its protein targets. Applying immunoprecipitation followed by mass spectrometry analysis we have identified Hsp90 as a partner of PhLP2A. With pull down experiments, we have confirmed this interaction in protein lysate and using purified proteins we have shown that PhLP2A interacts directly with Hsp90. Furthermore, the proximity ligation assay (PLA) performed on mIMCD-3 cells has shown that PhLP2A forms complexes with Hsp90 which are mainly localized in the cytoplasm of these cells. Further analysis has indicated that the level of PhLP2A increases after heat shock or radicicol treatment, similarly as the level of Hsp90, and that expression of PhLP2A after heat shock is regulated at the transcriptional level. Moreover, using recombinant luciferase we have shown that PhLP2A stabilizes this enzyme in a folding competent state and prevents its denaturation and aggregation. In addition, overexpression of PhLP2A in HEK-293 cells leads to increased heat stress resistance. Altogether, our results have shown that PhLP2A interacts with Hsp90 and exhibits molecular chaperone activity toward denatured proteins. J. Cell. Biochem. 118: 420-429, 2017.