Kelliher, M. A. | Search bioRxiv

bioRxiv2024

Raver1 links Ripk1 RNA splicing to caspase-8-mediated pyroptotic cell death, inflammation, and pathogen resistance

Multiple cell death and inflammatory signaling pathways converge on two critical factors: receptor interacting serine/threonine kinase 1 (RIPK1) and caspase-8. Careful regulation of these molecules is critical to control apoptosis, pyroptosis and inflammation. Here we discovered a pivotal role of Raver1 as an essential regulator of Ripk1 pre-mRNA splicing, expression, and functionality, and the subsequent caspase-8-dependent inflammatory cell death. Macrophages from Raver1-deficient mice exhibit altered splicing of Ripk1, accompanied by diminished cell death and reduced activation of caspase-8, Gasdermin D and E, caspase-1, as well as decreased interleukin-18 (IL-18) and IL-1{beta} production. These effects were triggered by Yersinia bacteria, or by restraining TAK1 or IKK{beta} in the presence of LPS, TNF family members, or IFN{gamma}. Consequently, animals lacking Raver1 showed heightened susceptibility to Yersinia infection. Raver1 and RIPK1 also controlled the expression and function of the C-type lectin receptor Mincle. Our study underscores the critical regulatory role of Raver1 in modulating innate immune responses and highlights its significance in directing in vivo and in vitro inflammatory processes. SignificanceCaspase-8 and the kinase RIPK1 are at focal points of several inflammation and cell death pathways. Thus, a careful regulation of their actions is needed. Our work identifies the RNA splicing factor Raver1 as a critical factor directing the splicing of Ripk1 in order to modulate RIPK1/caspase-8-driven pyroptosis, apoptosis and inflammation. Raver1 is central for macrophage responses to Yersinia bacteria, initiated after blockade of kinases TAK1 and IKK, measured as activation of RIPK1, caspase-8, Gasdermin D, caspase-3, IL-1{beta} and IL-18. Importantly, Raver1 is necessary for host resistance to Yersinia infection in vivo. We propose that Raver1 is key for correct tuning of RIPK1-caspase-8 dependent processes.

immunology↗

bioRxiv2024

Focal Deletions of a Promoter Tether Activate the IRX3 Oncogene in T Cell Acute Lymphoblastic Leukemia

Oncogenes can be activated in cis through multiple mechanisms including enhancer hijacking events and noncoding mutations that create enhancers or promoters de novo. These paradigms have helped parse somatic variation of noncoding cancer genomes, thereby providing a rationale to identify noncanonical mechanisms of gene activation. Here we describe a novel mechanism of oncogene activation whereby focal copy number loss of an intronic element within the FTO gene leads to aberrant expression of IRX3, an oncogene in T cell acute lymphoblastic leukemia (T-ALL). Loss of this CTCF bound element downstream to IRX3 (+224 kb) leads to enhancer hijack of an upstream developmentally active super-enhancer of the CRNDE long noncoding RNA (-644 kb). Unexpectedly, the CRNDE super-enhancer interacts with the IRX3 promoter with no transcriptional output until it is untethered from the FTO intronic site. We propose that promoter tethering of oncogenes to inert regions of the genome is a previously unappreciated biological mechanism preventing tumorigenesis.

cancer biology↗