Hsp70 binds to and stabilizes Nod2, an innate immune receptor involved in Crohn’s disease [Molecular Bases of Disease]

April 30th, 2014 by Mohanan, V., Grimes, C. L.

Microbes are detected by the pathogen−associated molecular patterns (PAMPs) through specific host pattern recognition receptors (PRR). Nucleotide binding oligomerization domain−containing protein 2 (Nod2) is an intracellular PRR that recognizes fragments of bacterial cell wall. Nod2 is important to human biology as when it is mutated it loses the ability to respond properly to bacterial cell wall fragments. In order to determine the mechanisms of misactivation in the Nod2 Crohn′s mutants, we developed a cell based system to screen for protein-protein interactors of Nod2. We identified heat shock protein 70 (Hsp70) as a protein interactor of both wild-type and Crohn′s mutant Nod2. Hsp70 has previously been linked with inflammation, especially in the regulation of anti−inflammatory molecules. Induced Hsp70 expression in cells increased Nod2 response to bacterial cell wall fragments. In addition, a Hsp70 inhibitor, KNK437, was capable of decreasing a Nod2 mediated NF−κb activation in response to bacterial cell wall stimulation. We found Hsp70 to regulate Nod2′s half-life, as increasing the Hsp70 level in cells increased Nod2′s half-life, and down-regulating Hsp70 decreased Nod2′s half-life. The expression level of the Crohn′s associated Nod2 variants were decreased compared to wild-type. The over-expression of Hsp70 significantly increased Nod2 levels as well as the signaling capacity of the mutants. Thus our study shows that restoring the stability of the Nod2 Crohn′s mutants is sufficient for rescuing the ability of these mutations to signal the presence of a bacterial cell wall ligand.