Role of p90 Ribosomal S6 Kinase (p90RSK) in Reactive Oxygen Species and Protein Kinase C β (PKC-β)-mediated Cardiac Troponin I Phosphorylation

Thunder Jalili,George L. King,Nadan Wang,Bo Ding,Jun-ichi Abe,Chen Yan,Christopher P. Bains,Seigo Itoh,Yasuchika Takeishi,Richard A. Walsh

doi:10.1074/jbc.m413015200

Abstract

Protein kinase C (PKC)-induced phosphorylation of cardiac troponin I (cTnI) depresses the acto-myosin interaction and may be important during the progression of heart failure. Although both PKCbetaII and PKCepsilon can phosphorylate cTnI, only PKCbeta expression and activity are elevated in failing human myocardium during end-stage heart failure. Furthermore, although increased cTnI phosphorylation was observed in mice with cardiac-specific PKCbeta II overexpression, no differences were observed in cTnI phosphorylation status between wild type and cardiac-specific PKCepsilon overexpression mice. A potentially important downstream effector of PKCs is p90 ribosomal S6 kinase (p90RSK), which plays an important role in cell growth by activating several transcription factors as well as Na+/H+ exchanger. Since both Ser23 and Ser24 of cTnI are contained in putative consensus sequences of p90RSK phosphorylation sites, we hypothesized that p90RSK is downstream from PKCbeta II and can be a cTnI (Ser(23/24)) kinase. p90RSK, but not ERK1/2 activation, was increased in PKCbetaII overexpression mice but not in PKCepsilon overexpression mice. p90RSK could phosphorylate cTnI in vitro with high substrate affinity but not cardiac troponin T (cTnT). To confirm the role of p90RSK in cTnI phosphorylation in vivo, we generated adenovirus containing a dominant negative form of p90RSK (Ad-DN-p90RSK). We found that the inhibition of p90RSK prevented H2O2-mediated cTnI (Ser(23/24)) phosphorylation but not ERK1/2 and PKCalpha/betaII activation. Next, we generated cardiac-specific p90RSK transgenic mice and observed that cTnI (Ser(23/24)) phosphorylation was significantly increased. LY333,531, a specific PKCbeta inhibitor, inhibited both p90RSK and cTnI (Ser(23/24)) phosphorylation by H2O2. Taken together, our data support a new redox-sensitive mechanism regulating cTnI phosphorylation in cardiomyocytes.

Highlights

Protein kinase C (PKC)-induced phosphorylation of cardiac troponin I depresses the acto-myosin interaction and may be important during the progression of heart failure
Since both Ser23 and Ser24 of cardiac troponin I (cTnI) are contained in putative consensus sequences of p90 ribosomal S6 kinase (p90RSK) phosphorylation sites, we hypothesized that p90RSK is downstream from PKC␤ II and can be a cTnI (Ser23/24) kinase. p90RSK, but not ERK1/2 activation, was increased in PKC␤II overexpression mice but not in PKC⑀ overexpression mice. p90RSK could phosphorylate cTnI in vitro with high substrate affinity but not cardiac troponin T
Since we found that p90RSK activation was increased in PKC␤II-Tg mice and that p90RSK could directly phosphorylate cTnI in vitro, we investigated whether PKC␤ can regulate H2O2-mediated p90RSK activation and subsequent dual TnI (Ser23/24) phosphorylation in cardiomyocytes

Summary

EXPERIMENTAL PROCEDURES

Protein Extract from Heart Tissue—Mouse hearts were washed with 10 ml of cold phosphate-buffered saline. P90RSK was immunoprecipitated through the incubation of 1000 ␮g of protein from each sample with 3 ␮l of rabbit polyclonal anti-p90RSK (Santa Cruz Biotechnology) antibody for 3 h followed by the addition of 40 ␮l of a 1:1 slurry of protein A/Sepharose beads to the extract/antibody mixture and incubation for 1 h at 4 °C This complex was washed, twice each, in cell lysis buffer described above, LiCl buffer (500 mM LiCl, 100 mM Tris-HCl (pH 7.6), 0.1% Triton X-100, 1 mM dithiothreitol) and wash buffer (20 mM Hepes, pH 7.2, 2 mM EGTA, 100 ␮M Na3VO4, 10 mM MgCl2, 1 mM dithiothreitol, 0.1% Triton X-100). Washed beads were incubated in 40 ␮l of assay dilution buffer (20 mM MOPS, pH 7.2, 25 mM ␤-glycerol phosphate, 5 mM EGTA, 1 mM sodium orthovanadate, and 1 mM dithiothreitol), 10 ␮l of 150-␮m-long S6 kinase substrate peptide, 10 ␮Ci of [␥-32P]ATP (Amersham Bioscience), 100 ␮M ATP, and 15 mM MgCl for 30 min at 30 °C. Differences were analyzed with one- or two-way repeated measures analysis of variance as appropriate followed by Scheffe’s correction

RESULTS

Findings

DISCUSSION