Dimension++ - Conformational changes in NLRC5 function

NOD-like receptors (NLRs) are best known as fundamental innate immune sensors. Upon cellular perturbations, NLRs such as NLR CARD-containing (NLRC) 4 and NLR pyrin domain-containing (NLRP) 3, switch from an inactive/closed conformation to an open one allowing the formation of multimers known as inflammasomes. Inflammasomes cause the production of inflammatory mediators and pyroptotic cell death, and mutations of NLRP3 and NLRC4 favoring the open conformation have been identified in patients suffering from inflammatory disorders.

NLRC5, instead, exerts a unique activity among NLRs; it transcriptionally regulates Major Histocompatibility Complex class I (MHCI) genes, the core genes of the adaptive immune system. This NLR shuttles to the nucleus and occupies the promoter of MHCI genes, where it is expected to interact with epigenetic and transcription factors supporting transactivation. Despite its emerging relevance in anticancer immunity, the molecular mechanisms underlying NLRC5 function remain largely unknown.

Because of their profoundly different functions, the possibility that conformational changes similar to those of inflammasome-forming NLRs regulate NLRC5 activity has never been considered. However, NLRC5 shares domain organization and regulatory residues with NLRP3 and/or NLRC4. Our preliminary data demonstrate that mutation of such residues alters NLRC5’s transactivation ability, suggesting that conserved conformational mechanisms underlie the function of NLRC5. Notably, the identified mutations enhancing NLRC5’s transcriptional activity are predicted, based on in silico analyses, to destabilize its open conformation; this further suggests that NLRC5 is functional in a closed form. To test these novel hypotheses, we plan to (1) investigate the propensity of WT NLRC5 and of the mutants with supraphysiological transactivation activity to form monomers/multimers and adopt a closed/open conformation and (2) test their capacity to occupy the MHCI gene promoter and/or interact with epigenetic/transcription factors.

Gaining a structural understanding of NLRP3’s activation mechanism helped develop targeted therapeutic interventions, which are currently tested for clinical use. Unveiling the relevance of conformational changes in NLRC5-mediated transcription of MHCI genes, key for immunity, constitutes not only a timely endeavour, but also a step forward to the potential modulation of NLRC5 activity for cancer immunotherapy.