Cytoplasmic innate immune sensing by the caspase-4 non-canonical inflammasome promotes cellular senescence

Abstract

Cytoplasmic recognition of microbial lipopolysaccharides (LPS) in human cells is elicited by the caspase-4 and caspase-5 noncanonical inflammasomes, which induce a form of inflammatory cell death termed pyroptosis. Here we show that LPS-mediated activation of caspase-4 also induces a stress response promoting cellular senescence, which is dependent on the caspase-4 substrate gasdermin-D and the tumor suppressor p53. Furthermore, we found that the caspase-4 noncanonical inflammasome is induced and assembled in response to oncogenic RAS signaling during oncogene-induced senescence (OIS). Moreover, targeting caspase-4 expression in OIS showed its critical role in the senescence-associated secretory phenotype and the cell cycle arrest induced in cellular senescence. Finally, we observed that caspase-4 induction occurs in vivo in mouse models of tumor suppression and ageing. Altogether, we are showing that cellular senescence is induced by cytoplasmic LPS recognition by the noncanonical inflammasome and that this pathway is conserved in the cellular response to oncogenic stress.

Discovery of new senolytics using machine learning

“…2D) for senolytic activity in two model cell lines for oncogene-induced and therapy-induced senescence. We first assessed oncogene-induced senescence (OIS) in human diploid fibroblasts IMR90 transduced with the fusion protein ER:RAS (IMR90 ER:RAS), which induces oncogenic Ras G12V -mediated stress by addition of 4-hydroxytamoxifen (4-OHT) to the culture media [49]. Treatment of IMR90 ER:RAS cells with 4-OHT showed a decrease in proliferation, increased senescence associated β-galactosidase activity, induction of cell cycle inhibitor expression, and activation of the SASP when compared with control and 4-OHT untreated cells, indicating that the cells underwent oncogene-induced senescence (Supplementary Fig.…”

“…We focussed on therapy-induced senescence (TIS, Supplementary Fig. 5A), where human epithelial cancerous cells (A549) were induced to become senescent by addition of etoposide [49]. Cells were treated with 100 µM etoposide for 48 hours, followed by another three days of exposure to media in standard conditions.…”

Inflammasome activation: from molecular mechanisms to autoinflammation

“…Genetic depletion of caspase‐5 reduced the secretion of hallmark cytokine factors related to SASP, such as of IL‐1α, IL‐6, IL‐8 and MCP‐1 factors in fibroblasts 173 . In a different study, augmented expression levels and activation of caspase‐4, via cytosolic LPS, induced a senescence state and pyroptotic cell death in IMR‐90 fibroblasts 174 . This was reflected by raised levels of p16INK4a, p21CIP1 proteins, and increased activity of senescence‐associated‐β‐galactosidase.…”

“…173 In a different study, augmented expression levels and activation of caspase-4, via cytosolic LPS, induced a senescence state and pyroptotic cell death in IMR-90 fibroblasts. 174 This was reflected by raised levels of p16INK4a, p21CIP1 proteins, and increased activity of senescenceassociated-b-galactosidase.…”

“… 173 In a different study, augmented expression levels and activation of caspase‐4, via cytosolic LPS, induced a senescence state and pyroptotic cell death in IMR‐90 fibroblasts. 174 This was reflected by raised levels of p16INK4a, p21CIP1 proteins, and increased activity of senescence‐associated‐β‐galactosidase. Moreover, in vivo studies using NF‐κB KO mice showed a correlation in the expression levels of caspase‐11 with p21 in lung epithelial cells.…”