Down-regulation of RalGTPase-Activating Protein Promotes Colitis-Associated Cancer via NLRP3 Inflammasome Activation

Abstract

Ral activation impacts interleukin 1b production by nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3 inflammasome activation and enhances matrix metalloproteinase-9 and matrix metalloproteinase-13 expression in a newly established mouse colitis-associated cancer model. This study strongly showed that the Ras-likenucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3 inflammasome pathway is involved in the mechanism of colitis-associated cancer invasion. BACKGROUND & AIMS: Ral guanosine triphosphatase-activating protein a2 (RalGAPa2) is the major catalytic subunit of the negative regulators of the small guanosine triphosphatase Ral, a member of the Ras subfamily. Ral regulates tumorigenesis and invasion/ metastasis of some cancers; however, the role of Ral in colitisassociated cancer (CAC) has not been investigated. We aimed to elucidate the role of Ral in the mechanism of CAC. METHODS: We used wild-type (WT) mice and RalGAPa2 knockout (KO) mice that showed Ral activation, and bone marrow chimeric mice were generated as follows: WT to WT, WT to RalGAPa2 KO, RalGAPa2 KO to WT, and RalGAPa2 KO to RalGAPa2 KO mice. CAC was induced in these mice by intraperitoneal injection of azoxymethane followed by dextran sulfate sodium intake. Intestinal epithelial cells were isolated from colon tissues, and we performed complementary DNA microarray analysis. Cytokine expression in normal colon tissues and CAC was analyzed by quantitative polymerase chain reaction. RESULTS: Bone marrow chimeric mice showed that immune cell function between WT mice and RalGAPa2 KO mice was not significantly different in the CAC mechanism. RalGAPa2 KO mice had a significantly larger tumor number and size and a significantly higher proportion of tumors invading the submucosa than WT mice. Higher expression levels of matrix metalloproteinase-9 and matrix metalloproteinase-13 were observed in RalGAPa2 KO mice than in WT mice. The expression levels of interleukin 1b, NLRP3, apoptosis associated speck-like protein containing a CARD, and caspase-1 were apparently increased in the tumors of RalGAPa2 KO mice compared with WT mice. NLRP3 inhibitor reduced the number of invasive tumors. CONCLUSIONS: Ral activation participates in the mechanism of CAC development via NLRP3 inflammasome activation. (Cell

Dysregulation of RalA signaling through dual regulatory mechanisms exerts its oncogenic functions in hepatocellular carcinoma

“…[29,30] On the other hand, RalGAP complex 2 was reported to be inactivated in multiple malignancies including oral, [13] prostate, [14] bladder, [12] and colon cancers. [15] As we observed in this study, of the two catalytic subunits, RalGAPA2 but not RalGAPA1 was predominantly expressed in HCC cells at both transcript and protein levels. We further found that RalGAPA2 was frequently and significantly down-regulated in HCC tumors and, more importantly, this down-regulation was associated with poorer overall survival rates and poorer cellular differentiation.…”

“…[ 11 ] Recently, a series of studies has suggested that dysregulation of the RalGAP complex is present in multiple solid cancers, including those of the buccal cavity, prostate, bladder, and colon. [ 12 , 13 , 14 , 15 ] In addition, functional inactivation of the RalGAP complex could promote cell migration in vitro and enhance cancer metastasis in vivo in an RalA‐dependent manner. [ 12 , 13 , 14 ] Furthermore, the catalytic subunit of RalGAP has been suggested to be a previously undocumented critical tumor suppressor gene for liver carcinogenesis in a two‐step forward short hairpin RNA (shRNA)‐based library screening in mice.…”

Huoxiang Zhengqi alleviates azoxymethane/dextran sulfate sodium-induced colitis-associated cancer by regulating Nrf2/NF-κB/NLRP3 signaling

“…Nrf2 controls the adaptive response to oxidative stress (Hayes and Dinkova-Kostova, 2014), which can inhibit the phosphorylation of IKKα/β and IκBα, thereby inhibits NF-κB phosphorylation and nuclear translocation and thus inhibits the release of downstream pro-inflammatory cytokines (Wardyn et al, 2015). NLRP3 inflammasome is responsible for increased production of IL-1β (Iida et al, 2020), and suppressing NLRP3 inflammasome activation by inhibiting MKP1/NF-κB pathway could attenuate DSS-induced ulcerative colitis (Wei et al, 2021). HXZQ may regulate Nrf2/NF-κB signaling, thus inhibiting NLRP3 transcription (Wang et al, 2018).…”

Parallel Rap1>RalGEF>Ral and Ras signals sculpt theC. elegansnervous system

“…Ras binds and activates RalGEF, which in turn activates Ral. Ral is an oncogene (Gentry et al, 2014;Kashatus, 2013), and its GAP is a tumor suppressor (Beel et al, 2020;Gao et al, 2019;Iida et al, 2020;Oeckinghaus et al, 2014;Saito et al, 2013; RalGEF>Ral signaling in cell migration Uegaki et al, 2019). Of the two mammalian Ral orthologs, RalA is associated with tumor initiation and anchorage-independent growth and RalB is associated with invasion, metastasis and survival (Gentry et al, 2014;Kashatus, 2013).…”