Moustaqil, M. | bioRxiv Science

bioRxiv2020

A dominant-negative SOX18 mutant disrupts multiple regulatory layers essential to transcription factor activity.

Few genetically dominant mutations involved in human disease have been fully explained at the molecular level. In cases where the mutant gene encodes a transcription factor, the dominant-negative mode of action of the mutant protein is particularly poorly understood. Here, we studied the genome-wide mechanism underlying a dominant-negative form of the SOX18 transcription factor (SOX18RaOp) responsible for both the classical mouse mutant Ragged opossum and the human genetic disorder Hypotrichosis-Lymphedema-Telangiectasia-Renal Syndrome. Combing three single-molecule imaging assays in living cells, we found that SOX18RaOp disrupts the system through an accumulation of molecular interferences which impair several functional properties of the wild-type SOX18 protein, including its chromatin-binding dynamics. The dominant-negative effect is further amplified by recruiting the interactome of its wild-type counterpart, which perturbs regulatory nodes such as SOX7 and MEF2C. Our findings explain in unprecedented detail the multi-layered process that underpins the molecular etiology of dominant-negative transcription factor function.

cell biology↗

bioRxiv2020

SARS-CoV-2 proteases cleave IRF3 and critical modulators of inflammatory pathways (NLRP12 and TAB1): implications for disease presentation across species and the search for reservoir hosts.

The genome of SARS-CoV-2 (SARS2) encodes for two viral proteases (NSP3/ papain-like protease and NSP5/ 3C-like protease or major protease) that are responsible for cleaving viral polyproteins for successful replication. NSP3 and NSP5 of SARS-CoV (SARS1) are known interferon antagonists. Here, we examined whether the protease function of SARS2 NSP3 and NSP5 target proteins involved in the host innate immune response. We designed a fluorescent based cleavage assay to rapidly screen the protease activity of NSP3 and NSP5 on a library of 71 human innate immune proteins (HIIPs), covering most pathways involved in human innate immunity. By expressing each of these HIIPs with a genetically encoded fluorophore in a cell-free system and titrating in the recombinant protease domain of NSP3 or NSP5, we could readily detect cleavage of cognate HIIPs on SDS-page gels. We identified 3 proteins that were specifically and selectively cleaved by NSP3 or NSP5: IRF-3, and NLRP12 and TAB1, respectively. Direct cleavage of IRF3 by NSP3 could explain the blunted Type- I IFN response seen during SARS-CoV-2 infections while NSP5 mediated cleavage of NLRP12 and TAB1 point to a molecular mechanism for enhanced production of IL-6 and inflammatory response observed in COVID-19 patients. Surprisingly, both NLRP12 and TAB1 have each two distinct cleavage sites. We demonstrate that in mice, the second cleavage site of NLRP12 is absent. We pushed this comparative alignment of IRF-3 and NLRP12 homologs and show that the lack or presence of cognate cleavage motifs in IRF-3 and NLRP12 could contribute to the presentation of disease in cats and tigers, for example. Our findings provide an explanatory framework for in-depth studies into the pathophysiology of COVID-19 and should facilitate the search or development of more effective animal models for severe COVID-19. Finally, we discovered that one particular species of bats, Davids Myotis, possesses the five cleavage sites found in humans for NLRP12, TAB1 and IRF3. These bats are endemic from the Hubei province in China and we discuss its potential role as reservoir for the evolution of SARS1 and SASR2.

molecular biology↗