Computational Modeling of NLRP3 Identifies Enhanced ATP Binding and Multimerization in Cryopyrin-Associated Periodic Syndromes.

Cyropyrin-associated periodic syndromes (CAPS) are clinically distinct syndromes that encompass a phenotypic spectrum yet are caused by alterations in the same gene, NLRP3. Many CAPS cases and other NLRP3-autoinflammatory diseases (NLRP3-AIDs) are directly attributed to protein-coding alterations in NLRP3 and the subsequent dysregulation of the NLRP3 inflammasome leading to IL-1ß-mediated inflammatory states. Here, we used bioinformatics tools, computational modeling, and computational assessments to explore the proteomic consequences of NLRP3 mutations, which potentially drive NLRP3 inflammasome dysregulation. We analyzed 177 mutations derived from familial cold autoinflammatory syndrome (FCAS), Muckle-Wells Syndrome (MWS), and the non-hereditary chronic infantile neurologic cutaneous and articular syndrome, also known as neonatal-onset multisystem inflammatory disease (CINCA/NOMID), as well as other NLRP3-AIDs. We found an inverse relationship between clinical severity and the severity of predicted structure changes resulting from mutations in NLRP3. Bioinformatics tools and computational modeling revealed that NLRP3 mutations that are predicted to be structurally severely-disruptive localize around the ATP binding pocket and that specific proteo-structural changes to the ATP binding pocket lead to enhanced ATP binding affinity by altering hydrogen-bond and charge interactions. Furthermore, we demonstrated that NLRP3 mutations that are predicted to be structurally mildly- or moderately-disruptive affect protein-protein interactions, such as NLRP3-ASC binding and NLRP3-NLRP3 multimerization, enhancing inflammasome formation and complex stability. Taken together, we provide evidence that proteo-structural mechanisms can explain multiple mechanisms of inflammasome activation in NLRP3-AID.

Inflammasome Sensor NLRP1 Confers Acquired Drug Resistance to Temozolomide in Human Melanoma.

Cancer cells gain drug resistance through a complex mechanism, in which nuclear factor-κB (NF-κB) and interleukin-1ß (IL-1ß) are critical contributors. Because NACHT, LRR and PYD domains-containing protein (NLRP) inflammasomes mediate IL-1ß maturation and NF-κB activation, we investigated the role of inflammasome sensor NLRP1 in acquired drug resistance to temozolomide (TMZ) in melanoma. The sensitivity of melanoma cells to TMZ was negatively correlated with the expression levels of O6-methylguanine-DNA methyltransferase (MGMT), the enzyme to repair TMZ-induced DNA lesions. When MGMT-low human melanoma cells (1205Lu and HS294T) were treated with TMZ for over two months, MGMT was upregulated, and cells became resistant. However, the resistance mechanism was independent of MGMT, and the cells that acquired TMZ resistance showed increased NLRP1 expression, NLRP inflammasome activation, IL-1ß secretion, and NF-κB activity, which contributed to the acquired resistance to TMZ. Finally, blocking IL-1 receptor (IL-1R) signaling with IL-1R antagonist decreased TMZ-resistant 1205Lu tumor growth in vivo. Although inflammation has been associated with drug resistance in various cancers, our paper is the first to demonstrate the involvement of NLRP in the development of acquired drug resistance. Because drug-tolerant cancer cells become cross-tolerant to other classes of cancer drugs, NLRP1 might be a suitable therapeutic target in drug-resistant melanoma, as well as in other cancers.

NLRP1 Functions Downstream of the MAPK/ERK Signaling via ATF4 and Contributes to Acquired Targeted Therapy Resistance in Human Metastatic Melanoma.

The BRAF V600E mutation leads to constitutive activation of the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway and its downstream effector responses. Uncovering the hidden downstream effectors can aid in understanding melanoma biology and improve targeted therapy efficacy. The inflammasome sensor, NACHT, LRR, and PYD domains-containing protein 1 (NLRP1), is responsible for IL-1ß maturation and itself is a melanoma tumor promoter. Here, we report that NLRP1 is a downstream effector of MAPK/ERK signaling through the activating transcription factor 4 (ATF4), creating regulation in metastatic melanoma cells. We confirmed that the NLRP1 gene is a target of ATF4. Interestingly, ATF4/NLRP1 regulation by the MAPK/ERK pathway uses distinct mechanisms in melanoma cells before and after the acquired resistance to targeted therapy. In parental cells, ATF4/NLRP1 is regulated by the MAPK/ERK pathway through the ribosomal S6 kinase 2 (RSK2). However, vemurafenib (VEM) and trametinib (TRA)-resistant cells lose the signaling via RSK2 and activate the cAMP/protein kinase A (PKA) pathway to redirect ATF4/NLRP1. Therefore, NLRP1 expression and IL-1ß secretion were downregulated in response to VEM and TRA in parental cells but enhanced in drug-resistant cells. Lastly, silencing NLRP1 in drug-resistant cells reduced their cell growth and inhibited colony formation. In summary, we demonstrated that NLRP1 functions downstream of the MAPK/ERK signaling via ATF4 and is a player of targeted therapy resistance in melanoma. Targeting NLRP1 may improve the therapeutic efficacy of targeted therapy in melanoma.