STAT3 palmitoylation initiates a positive feedback loop that promotes the malignancy of hepatocellular carcinoma cells in mice

Pharmacologically targeting fatty acid synthase-mediated de novo lipogenesis alleviates osteolytic bone loss by directly inhibiting osteoclastogenesis through suppression of STAT3 palmitoylation and ROS signaling

Aberrant increases in osteoclast formation and/or activity are the underlying cause of bone loss in a variety of osteolytic diseases. Fatty acid synthase (Fasn)-mediated de novo lipogenesis (DNL) is one of the major lipid metabolic pathways and has been shown to play critical roles in diverse physiological and pathological processes. However, little is known about its role in osteoclastogenesis. Here, we investigate the direct role of DNL in osteoclastogenesis and its therapeutic potential in osteolytic diseases. We found that Fasn expression and DNL levels are upregulated during receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis. Inhibition of Fasn by shRNA knockdown or its pharmacological inhibitors (ASC40 and trans-C75) impairs osteoclast differentiation in vitro. Mechanistically, pharmacological inhibition of Fasn suppresses RANKL-induced c-Fos/NFATc1 expression and thus osteoclastogenesis partly by disrupting STAT3 palmitoylation, while promoting ROS scavenging to impair mitogen-activated protein kinase (MAPK) signaling. Finally, the therapeutic potential of ASC40 for the treatment of osteolytic bone loss is tested in two mouse models of osteolytic diseases, i.e. ovariectomy (OVX)-induced osteoporosis and titanium nanoparticle-induced calvarial osteolysis. The results show that ASC40 significantly attenuates bone loss and osteoclastogenesis in both models. In conclusion, our results demonstrate that Fasn-mediated DNL is a novel positive regulator of osteoclastogenesis and may serve as a promising therapeutic target for the treatment of osteoclast-driven osteolytic bone diseases.

Palmitoylation in cardiovascular diseases: Molecular mechanism and therapeutic potential

Cardiovascular disease is one of the leading causes of mortality worldwide, and involves complex pathophysiological mechanisms that encompass various biological processes and molecular pathways. Post-translational modifications of proteins play crucial roles in the occurrence and progression of cardiovascular diseases, among which palmitoylation is particularly important. Various proteins associated with cardiovascular diseases can be palmitoylated to enhance the hydrophobicity of their molecular subdomains. This lipidation can significantly affect some pathophysiological processes, such as metabolism, inflammation by altering protein stability, localization, and signal transduction. In this review, we narratively summarize recent advances in the palmitoylation of proteins related to cardiovascular diseases and discuss its potential as a therapeutic target.

The role of palmitoylation modifications in the regulation of bone cell function, bone homeostasis, and osteoporosis

Osteoporosis a is a metabolic bone disease caused by an imbalance in bone homeostasis, which is regulated by osteoblasts and osteoclasts. Protein palmitoylation modification is a post-translational modification that affects protein function, localization, and targeting by attaching palmitoyl groups to specific amino acid residues of proteins. Recent studies have shown that protein palmitoylation is involved in the regulation of osteoclast overproduction, osteoblast migration, osteogenic differentiation, dysfunctional autophagy, and endocrine hormone membrane receptors in osteoporosis. Exactly to what extent palmitoylation modifications can regulate osteoporosis, and whether palmitoylation inhibition can delay osteoporosis, is a key question that needs to be investigated urgently. In this review, we observed that palmitoylation modifications act mainly through two target cells - osteoblasts and osteoclasts - and that the targets of palmitoylation modifications are focused on plasma membrane proteins or cytosolic proteins of the target cells, which tend to assume the role of receiving extracellular signals. We also noted that different palmitoyl transferases acting on different substrate proteins exert conflicting regulation of osteoblast function. We concluded that the regulation of osteocyte function, bone homeostasis, and osteoporosis by palmitoylation modifications is multidimensional, diverse, and interconnected. Perfecting the palmitoylation modification network can enhance our ability to utilize post-translational modifications to resist osteoporosis and lay the foundation for targeting palmitoyl transferases to treat osteoporosis in the future.

PLOD1 promotes the malignancy of hepatocellular carcinoma by facilitating the NF-κB/IL-6/STAT3-dependent TCA cycle

Background & Aims

Procollagen lysyl hydroxylase 1 (PLOD1) is crucial in regulating collagen synthesis and cross-linking. However, its roles and underlying mechanisms in the progression of hepatocellular carcinoma (HCC) remain unclear. Herein, we aimed to investigate the underlying biological functions and mechanisms of PLOD1 in HCC.

Methods

The expression levels of PLOD1 in HCC were measured by qPCR, Western blot, and immunohistochemistry. Cell proliferation, apoptosis, and stemness were examined by CCK8, flow cytometry, sphere formation, and aldehyde dehydrogenase activity assays. The subcutaneous tumorigenicity model, orthotopic tumorigenicity model, and hepatotoxin-induced HCC model were used for in vivo experiments. RNA-sequence and untargeted metabolomics analysis were performed to identify underlying mechanisms.

Results

PLOD1 is found to be highly expressed in both human (p <0.0001) and mouse HCC (p <0.01) and is associated with a poor prognosis (p = 0.047). In vitro and in vivo experiments reveal that overexpression of PLOD1 promotes the proliferation and stemness of HCC cells. Meanwhile, the depletion of PLOD1 attenuates the occurrence and growth of HCC, leading to cell cycle arrest (p <0.01) and apoptosis (p <0.001) in HCC. Mechanistically, PLOD1 positively regulates the NF-κB/IL-6/STAT3 signaling pathway and accelerates TCA cycle metabolic reprogramming. Blocking the NF-κB/IL-6/STAT3 signaling pathway and TCA cycle can effectively mitigate PLOD1-induced proliferation and stemness of HCC cells.

Conclusions

Our study uncovers the PLOD1/NF-κB/IL-6/STAT3 axis as a therapeutic target for inhibiting the progression and stemness of HCC.

Impact and implications

The roles and underlying mechanisms of PLOD1 in the progression of HCC remain unclear. In this study, we report that PLOD1 is highly expressed in patients with HCC and promotes the proliferation and stemness of HCC cells by activating the NF-κB/IL-6/STAT3-dependent TCA cycle. Knocking down hepatic PLOD1 using adeno-associated virus results in reduced progression of HCC in mice, suggesting that PLOD1 may serve as a potential therapeutic target for HCC.

ATG9B-4 accelerates the proliferation and migration of liver cancer cells in an ARNTL-CDK5 pathway-dependent manner: A case-control study

Lnc ATG9B-4 aggravated the progression of liver cancer by up-regulating cyclin-dependent-kinase 5 (CDK5). It could be inferred that ATG9B-4 indirectly regulates the expression of CDK5 via lncRNA-mediated negative regulation of target genes. Therefore, the specific molecular mechanism by which ATG9B-4 regulates the malignant characteristics of liver cancer cells still needs further study. The differentially expressed genes were identified by mRNA sequencing in liver cancer cells transfected with or without ATG9B-4. Liver cancer cells were transfected with ATG9B-4, ARNTL, or si-CDK5. The expression of aryl basic helix-loop-helix ARNT like 1 (BMAL1, also known as ARNTL), CDK5, and ATG9B-4 was analyzed by real-time quantitative PCR and western blotting. The proliferation and invasion of the transfected cells were respectively analyzed by cell counting kit-8 and wound healing assays, respectively. The ARNTL expression was down-regulated in the liver cancer tissues and liver cancer cells transfected with ATG9B-4. Low ARNTL expression indicated poor overall survival in patients with liver cancer. The optical density of cells transfected with ATG9B-4 and ARNTL was significantly lower than that of cells transfected with ATG9B-4. The wound areas of cells transfected with ATG9B-4 and ARNTL were markedly wider than those of cells transfected with ATG9B-4. The expression of CDK5 was down-regulated in cells transfected with ARNTL. CDK5 knockdown partially attenuated the ATG9B-4-induced increase in proliferation and migration in liver cancer cells. ATG9B-4 deteriorated the proliferation and migration of liver cancer cells in an ARNTL-CDK5 pathway-dependent manner.

PRMT1-mediated modification of H4R3me2a promotes liver cancer progression by enhancing the transcriptional activity of SOX18

BACKGROUND

HCC is one of the most prevalent and deadliest malignancies worldwide, with a poor prognosis. Altered histone modifications have been shown to play a significant role in HCC. However, the biological roles and clinical relevance of specific histone modifications, such as the asymmetric dimethylation on arginine 3 of histone H4 (H4R3me2a), remain poorly understood in HCC.

METHODS

In this study, immunohistochemical staining was performed to assess histone H4R3me2a modification in 32 pairs of HCC tissues and corresponding adjacent nontumor liver tissues. Cellular-level experiments and subcutaneous xenograft models in nude mice were used to investigate the effects of silencing protein arginine methyltransferase 1 (PRMT1) with shRNA or pharmacologically blocking PRMT1 activity on HCC cell proliferation, migration, and invasion. RNA-seq analysis combined with Chip-qPCR validation was employed to explore the regulatory mechanism of PRMT1 on SOX18 expression. The downstream target of SOX18 was identified using the JASPAR database and a dual-luciferase reporter system.

RESULTS

The level of histone H4R3me2a modification was significantly elevated in HCC tissues and closely associated with poor prognosis in patients with HCC. Silencing PRMT1 or pharmacologically inhibiting its activity effectively suppressed the proliferation, migration, and invasion of HCC cells. Mechanistically, PRMT1 was found to regulate SOX18 expression by modulating histone H4R3me2a modification in the SOX18 promoter region. LOXL1 was identified as a downstream target of the transcription factor SOX18.

CONCLUSIONS

This study revealed the clinical relevance of histone H4R3me2a modification in HCC and demonstrated that PRMT1 promotes malignant behavior in HCC cells by modulating H4R3me2a modification in the SOX18 promoter region. The findings elucidate the role and molecular mechanism of PRMT1-mediated histone H4R3me2a modification in HCC progression and highlight the potential clinical applications of PRMT1 inhibitors. These results may provide new insights into the treatment of HCC.

Palmitoylation of GPX4 via the targetable ZDHHC8 determines ferroptosis sensitivity and antitumor immunity

Ferroptosis is closely linked with various pathophysiological processes, including aging, neurodegeneration, ischemia-reperfusion injury, viral infection and, notably, cancer progression; however, its post-translational regulatory mechanisms remain incompletely understood. Here we revealed a crucial role of S-palmitoylation in regulating ferroptosis through glutathione peroxidase 4 (GPX4), a pivotal enzyme that mitigates lipid peroxidation. We identified that zinc finger DHHC-domain containing protein 8 (zDHHC8), an S-acyltransferase that is highly expressed in multiple tumors, palmitoylates GPX4 at Cys75. Through small-molecule drug screening, we identified PF-670462, a zDHHC8-specific inhibitor that promotes the degradation of zDHHC8, consequently attenuating GPX4 palmitoylation and enhancing ferroptosis sensitivity. PF-670462 inhibition of zDHHC8 facilitates the CD8+ cytotoxic T cell-induced ferroptosis of tumor cells, thereby improving the efficacy of cancer immunotherapy in a B16-F10 xenograft model. Our findings reveal the prominent role of the zDHHC8-GPX4 axis in regulating ferroptosis and highlight the potential application of zDHHC8 inhibitors in anticancer therapy.

Regulation of pattern recognition receptor signaling by palmitoylation

Pattern recognition receptors (PRRs), consisting of Toll-like receptors, RIG-I-like receptors, cytosolic DNA sensors, and NOD-like receptors, sense exogenous pathogenic molecules and endogenous damage signals to maintain physiological homeostasis. Upon activation, PRRs stimulate the sensitization of nuclear factor κB, mitogen-activated protein kinase, TANK-binding kinase 1-interferon (IFN) regulatory factor, and inflammasome signaling pathways to produce inflammatory factors and IFNs to activate Janus kinase/signal transducer and activator of transcription signaling pathways, resulting in anti-infection, antitumor, and other specific immune responses. Palmitoylation is a crucial type of post-translational modification that reversibly alters the localization, stability, and biological activity of target molecules. Here, we discuss the available knowledge on the biological roles and underlying mechanisms linked to protein palmitoylation in modulating PRRs and their downstream signaling pathways under physiological and pathological conditions. Moreover, recent advances in the use of palmitoylation as an attractive therapeutic target for disorders caused by the dysregulation of PRRs were summarized.

Recapitulating the potential contribution of protein S-palmitoylation in cancer

Protein S-palmitoylation is a reversible form of protein lipidation in which the formation of a thioester bond occurs between a cysteine (Cys) residue of a protein and a 16-carbon fatty acid chain. This modification is catalyzed by a family of palmitoyl acyl transferases, the DHHC enzymes, so called because of their Asp-His-His-Cys (DHHC) catalytic motif. Deregulation of DHHC enzymes has been linked to various diseases, including cancer and infections. Cancer, a major cause of global mortality, is characterized by features like uncontrolled cell growth, resistance to cell death, angiogenesis, invasion, and metastasis. Several of these processes are controlled by DHHC-mediated S-palmitoylation of oncogenes or tumor suppressors, including growth factor receptors (e.g., EGFR), kinases (e.g., AKT), and transcription factors (e.g., β-catenin). Dynamic regulation of S-palmitoylation is also governed by protein depalmitoylases. These enzymes balance the cycling of palmitoylation and regulate cellular signaling, cell growth, and its organization. Given the significance of S-palmitoylation in cancer, the DHHCs and protein depalmitoylases are promising targets for cancer therapy. Here we summarize the catalytic mechanisms of DHHC enzymes and depalmitoylases, their role in cancer progression and prevention, as well as the crosstalk of palmitoylation with other post-translational modifications. Additionally, we discuss the methods to detect S-palmitoylation, the limitations of available DHHC-targeting inhibitors, and ongoing research efforts to address these obstacles.

S-acylation of Ca2+ transport proteins in cancer

Alterations in cellular calcium (Ca2+) signals have been causally associated with the development and progression of human cancers. Cellular Ca2+ signals are generated by channels, pumps, and exchangers that move Ca2+ ions across membranes and are decoded by effector proteins in the cytosol or in organelles. S-acylation, the reversible addition of 16-carbon fatty acids to proteins, modulates the activity of Ca2+ transporters by altering their affinity for lipids, and enzymes mediating this reversible post-translational modification have also been linked to several types of cancers. Here, we compile studies reporting an association between Ca2+ transporters or S-acylation enzymes with specific cancers, as well as studies reporting or predicting the S-acylation of Ca2+ transporters. We then discuss the potential role of S-acylation in the oncogenic potential of a subset of Ca2+ transport proteins involved in cancer.

RNA-binding motif protein 28 enhances angiogenesis by improving STAT3 translation in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a prevalent malignant tumor characterized by extensive angiogenesis. However, the underlying mechanisms of HCC pathogenesis remain unclear. Previous studies have shown that RNA-binding proteins (RBPs) are implicated in HCC pathogenesis. In this study, we observed that increased RBM28 expression in HCC tissues was positively correlated with tumor microvascular density and negatively correlated with patient prognosis. Overexpression of RBM28 in HCC cells promoted tubule formation in human umbilical vein endothelial cells, whereas inhibition of RBM28 had the opposite effect, furthermore, the role of RBM28 in the progression of HCC was assessed using transgenic mouse models and chemically induced HCC models. We used various molecular assays and high-throughput detection methods to evaluate the role of RBM28 in promoting angiogenesis in HCC. Increased RBM28 expression in HCC directly binds to STAT3 mRNA, recruiting EIF4E to increase STAT3 expression and enhancing the secretion and expression of vascular endothelial growth factor A; consequently, promoting neovascularization in HCC. The potential of RBM28 as a viable diagnostic and therapeutic target for HCC was assessed using multi-cohort clinical samples and animal models. In summary, our results provide insights into the pathogenesis, clinical diagnosis, and treatment of HCC.

Therapeutic inhibition of the JAK-STAT pathway in the treatment of inflammatory bowel disease

Inflammatory bowel disease (IBD) encompasses a group of non-specific chronic intestinal inflammatory conditions of unclear etiology. The current treatment and long-term management primarily involve biologics. Nevertheless, some patients experience treatment failure or intolerance to biologics [1], making these patients a primary focus of IBD research. The Janus kinase (JAK)-Signal Transducers and Activator of Transcription (STAT) signal transduction pathway is crucial to the regulation of immune and inflammatory responses [2], and plays an important role in the pathogenesis of IBD. JAK inhibitors alleviate IBD by suppressing the transmission of JAK-STAT signaling pathway. As the first small-molecule oral inhibitor for IBD, JAK inhibitors greatly improved the treatment of IBD and have demonstrated significant efficacy, with tofacitinib and upadacitinib being approved for the treatment of ulcerative colitis (UC) [3]. JAK inhibitors can effectively alleviate intestinal inflammation in IBD patients who have failed to receive biologics, which may bring new treatment opportunities for refractory IBD patients. This review aims to elucidate the crucial roles of JAK-STAT signal transduction pathway in IBD pathogenesis, examine its role in various cell types within IBD, and explore the research progress of JAK inhibitors as therapeutic agents, paving the road for new IBD treatment strategies.

Metabolic Signaling in Cancer Metastasis

Metastases, which are the leading cause of death in patients with cancer, have metabolic vulnerabilities. Alterations in metabolism fuel the energy and biosynthetic needs of metastases but are also needed to activate cell state switches in cells leading to invasion, migration, colonization, and outgrowth in distant organs. Specifically, metabolites can activate protein kinases as well as receptors and they are crucial substrates for posttranslational modifications on histone and nonhistone proteins. Moreover, metabolic enzymes can have moonlighting functions by acting catalytically, mainly as protein kinases, or noncatalytically through protein-protein interactions. Here, we summarize the current knowledge on metabolic signaling in cancer metastasis.

SIGNIFICANCE

Effective drugs for the prevention and treatment of metastases will have an immediate impact on patient survival. To overcome the current lack of such drugs, a better understanding of the molecular processes that are an Achilles heel in metastasizing cancer cells is needed. One emerging opportunity is the metabolic changes cancer cells need to undergo to successfully metastasize and grow in distant organs. Mechanistically, these metabolic changes not only fulfill energy and biomass demands, which are often in common between cancer and normal but fast proliferating cells, but also metabolic signaling which enables the cell state changes that are particularly important for the metastasizing cancer cells.

NLRP3 Cys126 palmitoylation by ZDHHC7 promotes inflammasome activation

Nucleotide oligomerization domain (NOD)-like receptor protein 3 (NLRP3) inflammasome hyperactivation contributes to many human chronic inflammatory diseases, and understanding how NLRP3 inflammasome is regulated can provide strategies to treat inflammatory diseases. Here, we demonstrate that NLRP3 Cys126 is palmitoylated by zinc finger DHHC-type palmitoyl transferase 7 (ZDHHC7), which is critical for NLRP3-mediated inflammasome activation. Perturbing NLRP3 Cys126 palmitoylation by ZDHHC7 knockout, pharmacological inhibition, or modification site mutation diminishes NLRP3 activation in macrophages. Furthermore, Cys126 palmitoylation is vital for inflammasome activation in vivo. Mechanistically, ZDHHC7-mediated NLRP3 Cys126 palmitoylation promotes resting NLRP3 localizing on the trans-Golgi network (TGN) and activated NLRP3 on the dispersed TGN, which is indispensable for recruitment and oligomerization of the adaptor ASC (apoptosis-associated speck-like protein containing a CARD). The activation of NLRP3 by ZDHHC7 is different from the termination effect mediated by ZDHHC12, highlighting versatile regulatory roles of S-palmitoylation. Our study identifies an important regulatory mechanism of NLRP3 activation that suggests targeting ZDHHC7 or the NLRP3 Cys126 residue as a potential therapeutic strategy to treat NLRP3-related human disorders.