P38 kinases mediate NLRP1 inflammasome activation after ribotoxic stress response and virus infection

Inflammasomes integrate cytosolic evidence of infection or damage to mount inflammatory responses. The inflammasome sensor NLRP1 is expressed in human keratinocytes and coordinates inflammation in the skin. We found that diverse stress signals induce human NLRP1 inflammasome assembly by activating MAP kinase p38: While the ribotoxic stress response to UV and microbial molecules exclusively activates p38 through MAP3K ZAKα, infection with arthropod-borne alphaviruses, including Semliki Forest and Chikungunya virus, activates p38 through ZAKα and potentially other MAP3K. We demonstrate that p38 directly phosphorylates NLRP1 and that serine 107 in the linker region is critical for activation. NLRP1 phosphorylation is followed by ubiquitination of NLRP1PYD, N-terminal degradation of NLRP1, and nucleation of inflammasomes by NLRP1UPA-CARD. In contrast, activation of NLRP1 by nanobody-mediated ubiquitination, viral proteases, or inhibition of DPP9 was independent of p38 activity. Taken together, we define p38 activation as a unifying signaling hub that controls NLRP1 inflammasome activation by integrating a variety of cellular stress signals relevant to the skin.

Recessive NLRC4-Autoinflammatory Disease Reveals an Ulcerative Colitis Locus

PURPOSE

NLRC4-associated autoinflammatory disease (NLRC4-AID) is an autosomal dominant condition presenting with a range of clinical manifestations which can include macrophage activation syndrome (MAS) and severe enterocolitis. We now report the first homozygous mutation in NLRC4 (c.478G > A, p.A160T) causing autoinflammatory disease with immune dysregulation and find that heterozygous carriers in the general population are at increased risk of developing ulcerative colitis.

METHODS

Circulating immune cells and inflammatory markers were profiled and historical clinical data interrogated. DNA was extracted and sequenced using standard procedures. Inflammasome activation assays for ASC speck formation, pyroptosis, and IL-1β/IL-18 secretion confirmed pathogenicity of the mutation in vitro. Genome-wide association of NLRC4 (A160T) with ulcerative colitis was examined using data from the IBD exomes portal.

RESULTS

A 60-year-old Brazilian female patient was evaluated for recurrent episodes of systemic inflammation from six months of age. Episodes were characterized by recurrent low-grade fever, chills, oral ulceration, uveitis, arthralgia, and abdominal pain, followed by diarrhea with mucus and variable skin rash. High doses of corticosteroids were somewhat effective in controlling disease and anti-IL-1β therapy partially controlled symptoms. While on treatment, serum IL-1β and IL-18 levels remained elevated. Genetic investigations identified a homozygous mutation in NLRC4 (A160T), inherited in a recessive fashion. Increased ASC speck formation and IL-1β/IL-18 secretion confirmed pathogenicity when NLRC4 (A160T) was analyzed in human cell lines. This allele is significantly enriched in patients with ulcerative colitis: OR 2.546 (95% 1.778-3.644), P = 0.01305.

CONCLUSION

NLRC4 (A160T) can either cause recessively inherited autoinflammation and immune dysregulation, or function as a heterozygous risk factor for the development of ulcerative colitis.

Structure-guided multivalent nanobodies block SARS-CoV-2 infection and suppress mutational escape

The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to spread, with devastating consequences. For passive immunization efforts, nanobodies have size and cost advantages over conventional antibodies. In this study, we generated four neutralizing nanobodies that target the receptor binding domain of the SARS-CoV-2 spike protein. We used x-ray crystallography and cryo-electron microscopy to define two distinct binding epitopes. On the basis of these structures, we engineered multivalent nanobodies with more than 100 times the neutralizing activity of monovalent nanobodies. Biparatopic nanobody fusions suppressed the emergence of escape mutants. Several nanobody constructs neutralized through receptor binding competition, whereas other monovalent and biparatopic nanobodies triggered aberrant activation of the spike fusion machinery. These premature conformational changes in the spike protein forestalled productive fusion and rendered the virions noninfectious.