Acetylation of Heat Shock Protein 20 (Hsp20) Regulates Human Myometrial Activity

Abstract

Phosphorylation of heat shock protein 20 (Hsp20) by protein kinase A (PKA) is now recognized as an important regulatory mechanism modulating contractile activity in the human myometrium. Thus agonists that stimulate cyclic AMP production may cause relaxation with resultant beneficial effects on pathologies that affect this tissue such as the onset of premature contractions prior to term. Here we describe for the first time that acetylation of Hsp20 is also a potent post-translational modification that can affect human myometrial activity. We show that histone deacetylase 8 (HDAC8) is a non-nuclear lysine deacetylase (KDAC) that can interact with Hsp20 to affect its acetylation. Importantly, use of a selective linkerless hydroxamic acid HDAC8 inhibitor increases Hsp20 acetylation with no elevation of nuclear-resident histone acetylation nor marked global gene expression changes. These effects are associated with significant inhibition of spontaneous and oxytocin-augmented contractions of ex vivo human myometrial tissue strips. A potential molecular mechanism by which Hsp20 acetylation can affect myometrial activity by liberating cofilin is described and further high-lights the use of specific effectors of KDACs as therapeutic agents in regulating contractility in this smooth muscle.In developed countries premature birth prior to 37 weeks gestation accounts for nearly 75% of newborn deaths and is related to a high risk for survivors of long-term physical or mental disability (1). There are still no effective and safe therapeutic treatments for decreasing the incidence of premature deliveries. Accordingly, an increased understanding of the molecular mechanisms underlying myometrial activity is required to aid in the development of new strategies for the treatment of premature labor. To this end, recent evidence indicates a novel role for post-translational modification by acetylation in regulating myometrial activity. This was first highlighted by the class I/II histone deacetylase inhibitors (HDACIs) 3 TSA, VPA, and SBHA effecting relaxations of ϳ60% to spontaneously or oxytocin-mediated contracting human myometrial tissues ex vivo (2). Potential epigenetic events resulting from increased histone acetylation seem to be excluded due to the comparatively short time period observed for contractile inhibition of 20 -60 min. This pointed to the above HDACIs having non-epigenetic effects involving increased acetylation of lysine residues of protein components of the myometrial contractile machinery. This possibility is supported by recent proteomic findings of Kim et al. (3) and Choudhary et al. (4). They, respectively, showed that administration of the HDACIs TSA/Sirtinol to HeLa or SAHA/MS-275 to leukemia MV4 -11 cell cultures resulted in acetylation of a range of non-nuclear proteins. Importantly, proteins involved in regulating the cytoskeletal/filamentous architecture of cells were observed to be acetylated. These included actin, cofilin, 14-3-3 as well as the heat shock family protein member Hsp27.

Critical Role for Heat Shock Protein 20 (HSP20) in Migration of Malarial Sporozoites

“…The latter function is supported by biochemical and limited genetic data (9 -12). To explain the roles of sHSPs in actin dynamics, alternative modes of action, including direct competition with myosin binding to F-actin (13), alteration of actin attachment sites at membranedense plaques and cytoplasmic dense bodies (14), and sequestration of the 14-3-3 protein, resulting in liberation of cofilin (15,16), have been proposed. However, whether chaperones play an important role in microfilament-dependent processes in vivo still remains an open question.…”

Inhibition of Interleukin 1β (IL-1β) Expression by Anthrax Lethal Toxin (LeTx) Is Reversed by Histone Deacetylase 8 (HDAC8) Inhibition in Murine Macrophages

“…However, contribution of these genes to LPS immune responses is unknown. In addition, several proteins, including protein phosphatase (PP) 1, heat shock proteins, cofilin, ␣-actin, the structural maintenance of chromosome-3 (SMC3), ARID1A, MLL2, and the estrogen-related receptor-␣, have been shown to interact with HDAC8 (65,(71)(72)(73)(74)(75). Involvement of these proteins in immune responses has yet to be explored.…”

Regulation of GTP-binding Protein (Gαs) Expression in Human Myometrial Cells

“…Influence of Non-genomic Protein Acetylation-Previous work has also demonstrated a key role for lysine acetylation of Hsp20 (68). This post-translational modification was seen to govern the interaction between Hsp20 and cofilin.…”

“…Moreover, it would also suggest that in the context of myometrial function a cautious approach to using HDAC inhibitors as tocolytic (labor-stopping) drugs should be used. Briefly, there is a growing body of literature interested in understanding whether HDAC inhibitors may be of use clinically as tocolytic drugs (17,49,68). Although such studies do present convincing evidence that HDAC inhibitors such as TSA exert robust prorelaxant effects on isolated strips of human myometrium (Refs.…”