Abstract 2680: Nonautoinhibitory properties of the C-terminal helix of the mitogen- and stress-activated protein kinase 1

Abstract

Abstract Mitogen- and stress-activated protein kinase 1 (MSK1) is a growth factor-stimulated serine/threonine kinase that is important in the regulation of gene transcription and proinflammatory cytokine stimulation. MSK1 is a dual kinase possessing two distinct kinase domains linked by a hydrophobic region. The C-terminal kinase domain (CTD MSK1) is an important regulatory domain activated by ERKs and p38 mitogen-activated protein kinases (MAPKs) in response to various cellular stimuli. The activity of full length MSK1 is controlled by multiple phosphorylation sites and is mediated through stimulation of the C-terminal kinase domain. We have determined the crystal structure of the isolated active CTD MSK1 (residues 414-738) in apo- form and in complex with the non-hydrolyzable ATP analogue AMP-PNP at 2.0 and 2.5 Å resolution, respectively. The structure showed that, despite overall similarity with the p90 ribosomal S6 kinase 2 (RSK2) and the MAPK-activated protein kinase 2 (MK2), the CTD MSK1 is unexpectedly not autoinhibited by the C-terminal αL-helix. The helix does not form hydrogen bonds with a substrate-binding loop and nearby helices and lacks putative “inhibitory” residues responsible for the interaction with the kinase core. CTD MSK1 undergoes active autophosphorylation in vitro as shown by luminescent assay, and mutation of two residues, H712K and F719Y, located on the αL-helix does not convert it to RSK2-like autoinhibitory state. The protein was phosphorylated at Thr581 in the T-activation loop, and a T581A mutant showed significantly impaired autokinase activity. The “full length” C-terminal domain of MSK1 (residues 414-802) possessed weaker autophosphorylation activity compared with the truncated fragment (residues 414-738), which lacks the MAPK-docking site. Overexpression of active truncated CTD MSK1 (residues 414-738) in JB6 cells resulted in neoplastic transformation in response to EGF or TPA stimulation in a manner similar to that induced by the full length MSK1. On the other hand, the “full length” CTD (residues 414-802) suppressed colony formation ex vivo. This results indicate that the extreme C-terminal tail (residues 739-802), which encloses the ERK/p38 docking site, inhibits CTD MSK1 kinase activity. Using surface plasmon resonance (SPR) binding experiments, we showed that the C-terminal end-deleted construct does not interact with ERK1 in vitro, but the “full length” CTD MSK1 binds with ERK1 in a dose-dependent manner with a KD ∼ 70 nM. Similar binding results were obtained for interaction with ERK2 and p38. The SPR data indicate that the αL-helix is not involved in the interaction with MAP kinases. The intrinsic non-autoinhibitory C-terminal αL-helix feature suggests that the CTD has a αL-helix-independent activation mechanism, and the MAPK-docking site may regulate CTD MSK1 activity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2680.