Xiaojian Wang

High-fat diet (HFD) is a risk factor for metabolic dysfunction-associated steatotic liver disease (MASLD), yet the molecular pathways that connect dietary fats to liver dysfunction remain unclear. Here, we discover that hepatic downregulation of Raf kinase inhibitory protein (RKIP) in MASLD patients and male mice is linked to fatty acid uptake, which causes endoplasmic reticulum (ER)-associated degradation of RKIP by inhibiting its S-palmitoylation. Via facilitating the m⁶A-modified RNA binding of YTHDF1, RKIP is required for the efficient translation of PEMT, an essential enzyme in maintaining phosphatidylcholine (PC) / phosphatidylethanolamine (PE) ratio and ER homeostasis. Hepatocyte-specific RKIP depletion in male mice exacerbates the PC/PE imbalance and ER stress, resulting in lipid droplets accumulation and MASLD progression. Notably, RKIP correlates positively with PEMT protein but inversely with MASLD development. These findings uncover a cellular mechanism of HFD-RKIP-PEMT that underlies diet-induced liver metabolic disease and propose RKIP as a target for MASLD prevention.

Dysregulated tissue‐resident macrophages (TRMs) contribute to the pathogenesis of inflammatory bowel disease (IBD) and multiple sclerosis (MS). Uncovering molecular regulators of the divergent role of TRMs in inflammation can advance therapeutic strategies for autoimmune disorders. Here, a significant downregulation of SMAD‐specific E3 ubiquitin protein ligase 2 (SMURF2) is reported in TRMs within inflamed intestinal tissues from both IBD patients and mouse models. Notably, TRM‐specific deficiency of Smurf2 significantly exacerbates TRM proliferation in dextran sulfate sodium (DSS)‐induced colitis and experimental autoimmune encephalomyelitis (EAE), leading to augmented autoimmune inflammation. Mechanistically, SMURF2 interacts with phosphorylated TBK1 (p‐TBK1), mediating its Lys‐27‐linked ubiquitination and its subsequent lysosomal degradation, thereby suppressing TRM proliferation and autoimmune inflammation. Collectively, these findings establish SMURF2 as a pivotal mediator of TRM proliferation and autoimmune inflammation via p‐TBK1 modulation. Given that impaired SMURF2 expression correlates with the progression of autoimmune inflammation, SMURF2 represents a potential target for autoimmune disease treatment.

As central cells involved in osteoimmunology, bone niche macrophages possess diverse functions, and their differentiation fate regulates bone homeostasis. Elucidation of the underlying mechanism involved in macrophage differentiation is important for developing new therapeutic targets for osteoporosis. Here, we show that knocking out Raf kinase inhibitor protein (RKIP), either globally or in macrophages, results in dramatically increased bone mass in mice due to synergistic inhibition of bone resorption and promotion of bone formation. Mechanistically, RKIP knockout inhibits differentiation of macrophages into osteoclasts and promotes their differentiation towards pro-angiogenic subclusters, which enhances formation of H-type vessels. RKIP enhances osteoclastogenesis by interacting with ARHGAP to suppress CDC42 inactivation. Intranuclear RKIP suppresses angiogenic genes expression by bridging the association between HIF-1α and VHL to reduce the protein stability of HIF-1α in macrophages. Furthermore, RKIP deletion or inhibitor rescues ovariectomy (OVX)-induced bone loss in vivo. Collectively, this study provides insights into the different roles of extranuclear or intranuclear RKIP in regulating differentiation of bone niche macrophages and could inform potential therapies for bone homeostasis-related diseases.

Gasdermin (GSDM) family proteins mediate tumor pyroptosis and impact cancer progression, but other than that, their involvement in the tumor immune microenvironment remains largely unknown. Here, we show that activation of GSDMD in human tumor specimens mainly occurs in tumor-infiltrating leukocytes. Significantly, GSDMD deficiency or its inactivation in CD4 ⁺ T cells disabled CD8 ⁺ T cell–mediated antitumor immunity and caused tumor outgrowth in mice. Further study uncovered that, via inducing IL-2 production, GSDMD was required for CD4 ⁺ T cells to provide help to CD8 ⁺ T cell function. Mechanistically, GSDMD was cleaved by TCR stimulation–activated caspase-8 to form GSDMD-N pores, which enhanced Ca ²⁺ influx for IL-2 induction. Moreover, GSDMD activation and function were conserved in human CD4 ⁺ T cells and associated with favorable prognosis and improved response to anti–PD-1 immunotherapy in colonic and pancreatic cancer. We believe this study identifies a new nonpyroptotic role of GSDMD in tumor immunity, proposing GSDMD as a potential target for cancer immunotherapy.

Various factors play key roles in maintaining intestine homeostasis. Disruption of the balance may lead to inflammatory bowel diseases and even colorectal cancer (CRC). Loss or gain of function of many key proteins can result in dysregulated intestinal homeostasis. Our research demonstrated that neural precursor cells expressed developmentally downregulated 4–like protein (NEDD4L, or NEDD4-2), a type of HECT family E3 ubiquitin ligase, played an important role in maintaining intestinal homeostasis. NEDD4L expression was significantly inhibited in intestinal epithelial cells (IECs) of patients with Crohn’s disease, ulcerative colitis, and CRC. Global KO of NEDD4L or its deficiency in IECs exacerbated colitis induced by dextran sulfate sodium (DSS) and 2,4,6-trinitrobenzene sulfonic acid (TNBS) and CRC induced by azoxymethane and DSS. Mechanistically, NEDD4L deficiency in IECs inhibited expression of the key ferroptosis regulator glutathione peroxidase 4 (GPX4) by reducing the protein expression of solute carrier family 3 member 2 (SLC3A2) without affecting its gene expression, ultimately promoting DSS-induced IEC ferroptosis. Importantly, ferroptosis inhibitors reduced the susceptibility of NEDD4L-deficient mice to colitis and colitis-associated CRC. Thus, NEDD4L is an important regulator in IEC ferroptosis, maintaining intestinal homeostasis, making it a potential clinical target for diagnosing and treating IBDs.

Mechanical control is fundamental for cellular localization within a tissue, including for tumor-associated macrophages (TAMs). While the innate immune sensing pathways cGAS-STING and RLR-MAVS impact the pathogenesis and therapeutics of malignant diseases, their effects on cell residency and motility remain incompletely understood. Here, we uncovered that TBK1 kinase, activated by cGAS-STING or RLR-MAVS signaling in macrophages, directly phosphorylates and mobilizes Zyxin, a key regulator of actin dynamics. Under pathological conditions and in STING or MAVS signalosomes, TBK1-mediated Zyxin phosphorylation at S143 facilitates rapid recruitment of phospho-Zyxin to focal adhesions, leading to subsequent F-actin reorganization and reduced macrophage migration. Intratumoral STING-TBK1-Zyxin signaling was evident in TAMs and critical in antitumor immunity. Furthermore, myeloid-specific or global disruption of this signaling decreased the population of CD11b ⁺ F4/80 ⁺ TAMs and promoted PD-1-mediated antitumor immunotherapy. Thus, our findings identify a new biological function of innate immune sensing pathways by regulating macrophage tissue localization, thus providing insights into context-dependent mitigation of antitumor immunity.

Pattern recognition receptors (PRRs) play a crucial role in innate immunity, and a complex network tightly controls their signaling cascades to maintain immune homeostasis. Within the modification network, posttranslational modifications (PTMs) are at the core of signaling cascades. Conventional PTMs, which include phosphorylation and ubiquitination, have been extensively studied. The regulatory role of unconventional PTMs, involving unanchored ubiquitination, ISGylation, SUMOylation, NEDDylation, methylation, acetylation, palmitoylation, glycosylation, and myristylation, in the modulation of innate immune signaling pathways has been increasingly investigated. This comprehensive review delves into the emerging field of unconventional PTMs and highlights their pivotal role in innate immunity.

Cytosolic double-stranded DNA surveillance by cyclic GMP-AMP synthase (cGAS)–Stimulator of Interferon Genes (STING) signaling triggers cellular senescence, autophagy, biased mRNA translation, and interferon-mediated immune responses. However, detailed mechanisms and physiological relevance of STING-induced senescence are not fully understood. Here, we unexpectedly found that interferon regulatory factor 3 (IRF3), activated during innate DNA sensing, forms substantial endogenous complexes in the nucleus with retinoblastoma (RB), a key cell cycle regulator. The IRF3-RB interaction attenuates cyclin-dependent kinase 4/6 (CDK4/6)–mediated RB hyperphosphorylation that mobilizes RB to deactivate E2 family (E2F) transcription factors, thereby driving cells into senescence. STING-IRF3-RB signaling plays a notable role in hepatic stellate cells (HSCs) within various murine models, pushing activated HSCs toward senescence. Accordingly, IRF3 global knockout or conditional deletion in HSCs aggravated liver fibrosis, a process mitigated by the CDK4/6 inhibitor. These findings underscore a straightforward yet vital mechanism of cGAS-STING signaling in inducing cellular senescence and unveil its unexpected biology in limiting liver fibrosis.

Immunotherapy targeting PD‐L1 is still ineffective for a wide variety of tumors with high unpredictability. Deploying combined immunotherapy with alternative targeting is practical to overcome this therapeutic resistance. Here, the deficiency of serine‐threonine kinase STK24 is observed in tumor cells causing substantial attenuation of tumor growth in murine syngeneic models, a process relying on cytotoxic CD8⁺ T and NK cells. Mechanistically, STK24 in tumor cells associates with and directly phosphorylates AKT at Thr21, which promotes AKT activation and subsequent PD‐L1 induction. Deletion or inhibition of STK24, by contrast, blocks IFN‐γ‐mediated PD‐L1 expression. Various murine models indicate that in vivo silencing of STK24 can significantly enhance the efficacy of the anti‐PD‐1 blockade strategy. Elevated STK24 levels are observed in patient specimens in multiple tumor types and inversely correlated with intratumoral infiltration of cytotoxic CD8⁺ T cells and with patient survival. The study collectively identifies STK24 as a critical modulator of antitumor immunity, which engages in AKT and PD‐L1/PD‐1 signaling and is a promising target for combined immunotherapy.