Impact of Immunomodulatory Therapy on COVID-19 Vaccine Response in Patients with Autoimmune Inflammatory Rheumatic Diseases.

Coronavirus disease 2019 (COVID-19) vaccination is essential for patients with autoimmune inflammatory rheumatic diseases (AIIRD) to reduce the risk of morbidity and mortality associated with serious COVID-19 infection. With endemicity, waning of vaccine- and infection-acquired immunity, and development of SARS-CoV-2 variants, the need for additional doses of vaccines against serious illness in high-risk immunocompromised persons remains imperative. This review examines how immunomodulatory therapies affect vaccine-induced immune response in patients with AIIRD. Glucocorticoids, methotrexate, azathioprine, calcineurin inhibitors, mycophenolate mofetil, tumor necrosis factor inhibitors, and abatacept have been shown to variably attenuate both humoral and cellular immune responses to vaccination. Janus kinase inhibitors reduce humoral immune response. In contrast, sulfasalazine, leflunomide, belimumab, interleukin (IL)-17, IL-12/23, IL-6, and IL-1 inhibitors appear favorable, with mild or no impact on vaccine response. Although rituximab is known to profoundly diminish humoral immune response, cellular immunity is relatively preserved. Administering a third and subsequent vaccine dose or temporally coordinating the dosing of immunomodulatory drugs may improve vaccine effectiveness. Further research is needed to personalise vaccination strategies for AIIRD patients, considering their specific immunomodulatory treatments.

Structural Basis for the Enzymatic Activity of the HACE1 HECT-Type E3 Ligase Through N-Terminal Helix Dimerization.

HACE1 is an ankyrin repeat (AKR) containing HECT-type E3 ubiquitin ligase that interacts with and ubiquitinates multiple substrates. While HACE1 is a well-known tumor suppressor, its structure and mode of ubiquitination are not understood. The authors present the cryo-EM structures of human HACE1 along with in vitro functional studies that provide insights into how the enzymatic activity of HACE1 is regulated. HACE1 comprises of an N-terminal AKR domain, a middle (MID) domain, and a C-terminal HECT domain. Its unique G-shaped architecture interacts as a homodimer, with monomers arranged in an antiparallel manner. In this dimeric arrangement, HACE1 ubiquitination activity is hampered, as the N-terminal helix of one monomer restricts access to the C-terminal domain of the other. The in vitro ubiquitination assays, hydrogen-deuterium exchange mass spectrometry (HDX-MS) analysis, mutagenesis, and in silico modeling suggest that the HACE1 MID domain plays a crucial role along with the AKRs in RAC1 substrate recognition.

HOX epimutations driven by maternal SMCHD1/LRIF1 haploinsufficiency trigger homeotic transformations in genetically wildtype offspring.

The body plan of animals is laid out by an evolutionary-conserved HOX code which is colinearly transcribed after zygotic genome activation (ZGA). Here we report that SMCHD1, a chromatin-modifying enzyme needed for X-inactivation in mammals, is maternally required for timely HOX expression. Using zebrafish and mouse Smchd1 knockout animals, we demonstrate that Smchd1 haplo-insufficiency brings about precocious and ectopic HOX transcription during oogenesis and embryogenesis. Unexpectedly, wild-type offspring born to heterozygous knockout zebrafish smchd1 mothers exhibited patent vertebrate patterning defects. The loss of maternal Smchd1 was accompanied by HOX epi-mutations driven by aberrant DNA methylation. We further show that this regulation is mediated by Lrif1, a direct interacting partner of Smchd1, whose knockout in zebrafish phenocopies that of Smchd1. Rather than being a short-lived maternal effect, HOX mis-regulation is stably inherited through cell divisions and persists in cultured fibroblasts derived from FSHD2 patients haploinsufficient for SMCHD1. We conclude that maternal SMCHD1/LRIF1 sets up an epigenetic state in the HOX loci that can only be reset in the germline. Such an unusual inter-generational inheritance, whereby a phenotype can be one generation removed from its genotype, casts a new light on how unresolved Mendelian diseases may be interpreted.

Exploring the "Other" subfamily of HECT E3-ligases for therapeutic intervention.

The HECT E3 ligase family regulates key cellular signaling pathways, with its 28 members divided into three subfamilies: NEDD4 subfamily (9 members), HERC subfamily (6 members) and "Other" subfamily (13 members). Here, we focus on the less-explored "Other" subfamily and discuss the recent findings pertaining to their biological roles. The N-terminal regions preceding the conserved HECT domains are significantly diverse in length and sequence composition, and are mostly unstructured, except for short regions that incorporate known substrate-binding domains. In some of the better-characterized "Other" members (e.g., HUWE1, AREL1 and UBE3C), structure analysis shows that the extended region (~ aa 50) adjacent to the HECT domain affects the stability and activity of the protein. The enzymatic activity is also influenced by interactions with different adaptor proteins and inter/intramolecular interactions. Primarily, the "Other" subfamily members assemble atypical ubiquitin linkages, with some cooperating with E3 ligases from the other subfamilies to form branched ubiquitin chains on substrates. Viruses and pathogenic bacteria target and hijack the activities of "Other" subfamily members to evade host immune responses and cause diseases. As such, these HECT E3 ligases have emerged as potential candidates for therapeutic drug development.

Structural insights into a HECT-type E3 ligase AREL1 and its ubiquitination activities in vitro.

The HECT E3 ligase family comprises three subfamilies: NEDD4 E3 ubiquitin protein ligase (NEDD4), HECT and RLD domain-containing E3 ubiquitin protein ligase (HERC), and "other." Most previous studies have focused on the NEDD4 subfamily. Apoptosis-resistant E3 ligase 1 (AREL1) belongs to "other" subfamily HECT that inhibits apoptosis by ubiquitinating and degrading proapoptotic proteins. Here, we report the crystal structure of the extended HECT domain of AREL1 (amino acids (aa) 436-823) at 2.4 Å resolution and its ubiquitination of the proapoptotic protein second mitochondria-derived activator of caspase (SMAC). We found that the extended HECT domain adopts an inverted, T-shaped, bilobed conformation and harbors an additional loop (aa 567-573) absent in all other HECT members. We also show that the N-terminal extended region (aa 436-482) preceding the HECT domain is indispensable for its stability and activity and that without this region, the HECT domain becomes inactive. AREL1 ubiquitinated SMAC, primarily on Lys62 and Lys191 We solved the crystal structure of the tetrameric form of SMAC to 2.8 Å resolution, revealing the Lys62 and Lys191 locations. The AREL1 HECT domain assembled Lys33-, Lys48-, and Lys63-linked polyubiquitin chains. Moreover, E701A substitution in the AREL1 HECT domain substantially increased its autopolyubiquitination and SMAC ubiquitination activity, whereas deletion of the last three amino acids at the C terminus completely abrogated AREL1 autoubiquitination and reduced SMAC ubiquitination. Finally, an AREL1-specific ubiquitin variant inhibited SMAC ubiquitination in vitro Our findings may assist in the development of AREL1 inhibitors that block its anti-apoptotic activity in cancer.