Human AIM2 blocking peptide

Inflammasomes are key intracellular signaling platforms involved in innate immune responses to micro-organisms and danger signals. Extracellular signal-regulated kinase, Jun N-terminal kinase, and p38 mitogen-activated protein kinase family members are activated by numerous environmental stresses. Recently, it has been reported that Jun N-terminal kinase is involved in inflammasome activation in myeloid immune cells. To date, the role of mitogen-activated protein kinase in inflammasome activity in keratinocytes has not been investigated. Here, we show that, in primary human keratinocytes, p38 mitogen-activated protein kinase is required for inflammasome activation and IL-1 beta secretion. Using selective small molecule inhibitors, small interfering RNA gene silencing, and CRISPR/Cas9-based deletion, we demonstrate the above and identify p38 alpha and p38 delta as critical regulators of ASC oligomerization, inflammasome activation, and IL-1 beta secretion in keratinocytes. Furthermore, our data suggest that the nature of the mitogen-activated protein kinase regulating inflammasome activity exhibits a certain cell specificity, with p38 playing a predominant role in keratinocytes and Jun N-terminal kinase 1 in cells of myeloid origin.

Objective: Salmonella is known to evolve many mechanisms to avoid or delay inflammasome activation which remain largely unknown. In this study, we investigated whether the SopB protein critical to bacteria virulence capacity was an effector that involved in the regulation of inflammasome activation. Methods: BMDMs from NLRC4-, NLRP3-, caspase-1/-11-, IF116- and AIM2-deficient mice were pretreated with LPS, and subsequently stimulated with a series of SopB-related strains of Salmonella, inflammasome induced cell death, IL-1 beta secretion, cleaved caspase-1 production and ASC speckle formation were detected. Results: We found that SopB could inhibit host IL-1 beta secretion, caspase-1 activation and inflammasome induced cell death using a series of SopB-related strains of Salmonella; however the reduction of IL-1 beta secretion was not dependent on sensor that contain PYD domain, such as NLRP3, AIM2 or IF116, but dependent on NLRC4. Notably, SopB specifically prevented ASC oligomerization and the enzymatic activity of SopB was responsible for the inflammasome inhibition. Furthermore, inhibition of Akt signaling induced enhanced inflammasome activation. Conclusions: These results revealed a novel role in inhibition of NLRC4 inflammasome for Salmonella effector SopB.