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Inhibition of hsp27 Phosphorylation Increases Interaction with Hic5 in Vascular Myocytes

The small heat shock protein, hsp27, is a cytosolic ubiquitously expressed, stress responsive chaperone. It is phosphorylated rapidly in response to a variety of stressors via the p38 MAP kinase pathway. Hsp27 has been associated with and modulates a variety of essential proteins such as actin and cytochrome c. It has also been shown to bind to and be modulated by the paxillin homologue, Hic‐5 (hydrogen peroxide inducible clone 5, also known as ARA55 for androgen receptor activator 55kda). We sought to examine the nature of this interaction via co‐expressing hsp27‐cfp and Hic‐5‐mcitrine fusion proteins and confocal FRET methodology. Both fusions were adenovirally mounted to allow myocyte transduction. Of note, in neonatal cardiomyocytes and smooth muscle cells (SMCs) there was no measureable interaction under basal conditions. With 60 minute pretreatment of SMCs with the specific p38 inhibitor, SB203580 at 10uM, there was a marked increase in F485 vs basal and vs pretreatment with the MEK inhibitor PD90859 at 30 uM (63±3.9%*vs −5±5% vs −6.5±2.6%, respectively, n=9, *p=0.001 by ANOVA, post‐hoc Bonferroni). In contrast, inhibitor pretreatment produced no significant FRET in cardiomyocytes nor did the use of mutagenized nonphosphorylatable 3Ahsp27‐cfp in SMCs. We conclude that only nonphosphorylated hsp27 species interact with Hic‐5 and in specific cell types.