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Immune dysregulation in SHARPIN-deficient mice is dependent on CYLD-mediated cell death
Rosalind L Ang1, Mark Chan2,3, Diana Legarda2
1Precision Immunology Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029; rang.phd776@gmail.com ting.adrian@mayo.edu.
Abstract:
SHARPIN, together with RNF31/HOIP and RBCK1/HOIL1, form the linear ubiquitin chain assembly complex (LUBAC) E3 ligase that catalyzes M1-linked polyubiquitination. Mutations in RNF31/HOIP and RBCK/HOIL1 in humans and Sharpin in mice lead to autoinflammation and immunodeficiency, but the mechanism underlying the immune dysregulation remains unclear. We now show that the phenotype of the Sharpin mice is dependent on CYLD, a deubiquitinase previously shown to mediate removal of K63-linked polyubiquitin chains. Dermatitis, disrupted splenic architecture, and loss of Peyer's patches in the Sharpin mice were fully reversed in Sharpin mice. We observed enhanced association of RIPK1 with the death-signaling Complex II following TNF stimulation in Sharpin cells, a finding dependent on CYLD since we observed reversal in Sharpin cells. Enhanced RIPK1 recruitment to Complex II in Sharpin cells correlated with impaired phosphorylation of CYLD at serine 418, a modification reported to inhibit its enzymatic activity. The dermatitis in the Sharpin mice was also ameliorated by the conditional deletion of Cyld using LysM-cre or Cx3cr1-cre indicating that CYLD-dependent death of myeloid cells is inflammatory. Our studies reveal that under physiological conditions, TNF- and RIPK1-dependent cell death is suppressed by the linear ubiquitin-dependent inhibition of CYLD. The Sharpin phenotype illustrates the pathological consequences when CYLD inhibition fails.
Insights
The Sharpin protein deficiency causes immune problems by failing to inhibit CYLD, a deubiquitinase. Restoring CYLD inhibition reverses these inflammatory effects in mice.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- The linear ubiquitin chain assembly complex (LUBAC), comprising SHARPIN, RNF31/HOIP, and RBCK1/HOIL1, catalyzes M1-linked polyubiquitination.
- Mutations in LUBAC components cause autoinflammation and immunodeficiency, but the underlying mechanisms are not fully understood.
- CYLD is a deubiquitinase known to remove K63-linked polyubiquitin chains.
Purpose of the Study:
- To elucidate the mechanism by which SHARPIN deficiency leads to immune dysregulation.
- To investigate the role of CYLD in the autoinflammatory phenotype observed in Sharpin-deficient mice.
Main Methods:
- Analysis of Sharpin-deficient mouse models.
- Investigation of CYLD's role in Sharpin-deficient cells and tissues.
- Assessment of RIPK1 association with death-signaling Complex II.
- Examination of CYLD phosphorylation status.
- Conditional deletion of Cyld in myeloid cells.
Main Results:
- The autoinflammatory phenotype of Sharpin-deficient mice was dependent on CYLD and fully reversed by its absence.
- Sharpin deficiency led to enhanced RIPK1 recruitment to TNF-induced Complex II, linked to impaired CYLD phosphorylation.
- Deletion of CYLD ameliorated dermatitis in Sharpin-deficient mice, indicating CYLD-dependent myeloid cell death contributes to inflammation.
Conclusions:
- Under physiological conditions, linear ubiquitination by LUBAC inhibits CYLD activity, preventing TNF- and RIPK1-dependent cell death.
- SHARPIN deficiency disrupts this inhibitory mechanism, leading to pathological inflammation.
- The findings reveal a critical role for CYLD in suppressing inflammatory cell death pathways regulated by LUBAC.
