USP24-dependent stabilization of Runx2 recruits a p300/NCOA3 complex to transactivate ADAMTS genes and promote degeneration of intervertebral disc in chronic inflammation mice

Vitamin D deficiency promotes intervertebral disc degeneration via p38/NCoR2-mediated extracellular matrix degradation

PURPOSE

Vitamin D (VD) deficiency significantly contributes to intervertebral disc degeneration (IDD), a common cause of low back pain, yet the underlying mechanisms remain unclear. This study investigates how VD deficiency exacerbates IDD and identifies potential therapeutic targets.

METHODS

We used real-time quantitative PCR, immunoblots, immunoprecipitation, liquid chromatography with tandem mass spectrometry analysis, co-immunoprecipitation, and chromatin immunoprecipitation to study gene and protein expressions, protein complex assembly, and transcriptional complex binding. Degeneration of IVDs was assessed via hematoxylin and eosin staining.

RESULTS

Eight members of ADAMTSs (A disintegrin and metalloproteinase with thrombospondin motifs) are enriched in lumbar discs of both VD-deficient and VD receptor (VDR)-knockout (VDR-/-) mice. Sufficient VD suppresses ADAMTS genes through a complex formed by nuclear receptor corepressor 2 (NCoR2) and signal transducer and activator of transcription 6 (STAT6). VD deficiency activates p38 kinase, leading to NCoR2 phosphorylation and subsequent degradation by a Cullin 4-RING (CRL4) E3 ligase, impairing NCoR2's transrepression function and upregulating ADAMTS genes, accelerating extracellular matrix (ECM) degradation in discs. This mechanism is replicated in VDR-deficient cells. In vitro treatments with p38 inhibitor (BIRB-796) and CRL4 inhibitor (KH-4-43) reduce ADAMTS expression, and in vivo application of these inhibitors improves disc integrity in VD-deficient mice.

CONCLUSION

Our findings highlight NCoR2 degradation, mediated by p38 kinase and CRL4 E3 ligase, as crucial in VD deficiency-induced IDD. Targeting this pathway offers promising therapeutic potential to mitigate IDD progression in individuals with VD deficiency or VDR abnormalities.

Dysregulation of the p300/CBP histone acetyltransferases in human cancer

p300 (E1A binding protein 300) and CBP (CREB-binding protein) are critical regulators of chromatin dynamics and gene expression, playing essential roles in various cellular processes, including proliferation, differentiation, apoptosis, and immune responses. These homologous histone acetyltransferases (HATs) function as transcriptional co-activators by acetylating histones and non-histone proteins. p300/CBP is essential for development, and dysregulation of p300 and CBP has been implicated in several human diseases, particularly cancer. Somatic mutations that inactivate p300/CBP are frequently observed across various cancer types. Additionally, other mutations leading to translocations or truncations of p300/CBP can result in enhanced catalytic activity, potentially representing novel gain-of-function mutations that promote tumor progression. In this review, we discuss the mechanisms underlying the regulation of p300/CBP HAT activity, its dysregulation in cancer, and the development of p300/CBP inhibitors and their potential in cancer therapies.

Inflammatory microenvironment promotes extracellular matrix degradation of chondrocytes through ALKBH5-dependent Runx2 m6A modification in the pathogenesis of osteoarthritis

BACKGROUND

Osteoarthritis (OA) is a chronic degenerative joint disease characterized by the breakdown of cartilage and extracellular matrix (ECM). The degradation of ECM in chondrocytes plays a crucial role in OA pathogenesis, but the underlying molecular mechanisms remain largely unclear.

METHODS

A sodium monoiodoacetate (MIA) mouse model was used to mimic OA. ECM integrity was accessed by Hematoxylin and Eosin (H&E) staining, Safranin O/fast green staining, and microcomputerized tomography. Enzyme-linked immunosorbent assay measured circulating proinflammatory cytokines. Reverse transcription-quantitative polymerase chain reaction and western blotting analyzed mRNA and protein expression levels. RNA and chromatin immunoprecipitation evaluated RNA-protein and DNA-protein interactions.

RESULTS

MIA mice showed significant upregulation of the RNA m6A demethylase ALKBH5 (alkylated DNA repair protein AlkB homolog 5), the transcription factor Runx2 (runt-related transcription factor 2), and matrix-degrading enzymes Mmps (matrix metallopeptidase) and Adamts(s) (a disintegrin and metalloproteinase with thrombospondin motifs). In vitro, proinflammatory cytokines induced these proteins in chondrocytes. Mechanically, Alkbh5 cooperated with Ythdf1 (YTH N6-methyladenosine RNA binding protein 1) in the inflammatory microenvironment to regulate the expression and stability of RUNX2 mRNA. Runx2, in turn, activated the expression of MMPs and ADAMTSs, promoting ECM degradation in chondrocytes, thereby contributing to OA progression. Notably, inhibition of Alkbh5 and Runx2 in MIA-treated mice significantly alleviated the pathological progression of OA.

CONCLUSION

Our results reveal a novel mechanism of OA pathogenesis and suggest that targeting Alkbh5 and Runx2 may represent a new therapeutic strategy for OA treatment.

YTHDF2-dependent m6A modification of FOXO3 mRNA mediates TIMP1 expression and contributes to intervertebral disc degeneration following ROS stimulation

The accumulation of reactive oxygen species (ROS) significantly contributes to intervertebral disc degeneration (IDD), but the mechanisms behind this phenomenon remain unclear. This study revealed elevated ROS levels in the intervertebral discs (IVDs) of aged mice compared to those of younger mice. The local application of hydrogen peroxide (H2O2) near lumbar discs also induced ROS accumulation and IDD. Isobaric tags for relative and absolute quantitation (iTRAQ) analysis of discs from aged and H2O2-injected mice showed increased levels of YTH N6-methyladenosine RNA binding protein F2 (YTHDF2) and matrix metallopeptidase 1/3/7/9 (MMP1/3/7/9), along with decreased levels of forkhead box O3 (FOXO3) and TIMP1 (tissue inhibitor of metalloproteinases 1). Our experiments indicated that in nucleus pulposus (NP) cells and young mouse IVDs that were not exposed to ROS, FOXO3 recruited histone acetyltransferase CBP (CREB binding protein) and mediator complex subunit 1 (Med1) to activate TIMP1 expression, which inhibited MMP activity and prevented disc degeneration. However, ROS exposure activated YTHDF2 and promoted the degradation of m6A-modified FOXO3 mRNA, impairing FOXO3's ability to activate TIMP1. This degradation exacerbated MMP activity and contributed to the degradation of the IVD extracellular matrix. Notably, administration of the YTHDF2 inhibitor DC-Y13-27 in older and H2O2-treated mice significantly enhanced FOXO3 and TIMP1 expression, reduced MMP activity, and mitigated IVD degeneration. Together, this study uncovers a novel ROS-regulated pathway in IDD, centered on the YTHDF2/FOXO3/TIMP1/MMPs axis, suggesting that targeting YTHDF2 may represent a promising therapeutic strategy for combating the progression of IDD.

USP24 promotes autophagy-dependent ferroptosis in hepatocellular carcinoma by reducing the K48-linked ubiquitination of Beclin1

Ubiquitination is a post-translational modification (PTM), which is critical to maintain cell homeostasis. Ubiquitin-specific protease 24 (USP24) plays roles in various diseases, the mechanisms by which USP24 regulates hepatocellular carcinoma (HCC) remain poorly understood. In this study, USP24 is found to be significantly downregulated in HCC. Knocking down USP24 promotes HCC proliferation and migration, whereas USP24 overexpression inhibits HCC in vitro and in vivo. The endogenous interaction between USP24 and Beclin1 is confirmed. Mechanically, USP24 delays Beclin1 degradation by reducing its K48-linked ubiquitination, the effects of overexpressing USP24 on HCC proliferation can be partially reversed by silencing Beclin1. We find that increased autophagy is accompanied by ferroptosis in USP24 overexpressed HCC cells and USP24 increases the susceptibility of HCC to sorafenib. Collectively, this study highlights the critical role of USP24 in regulating autophagy-dependent ferroptosis by decreasing Beclin1 ubiquitination, suggesting that targeting USP24 may be a strategy for treating HCC.

Ubiquitin recruiting chimera: more than just a PROTAC

Ubiquitinylation of protein substrates results in various but distinct biological consequences, among which ubiquitin-mediated degradation is most well studied for its therapeutic application. Accordingly, artificially targeted ubiquitin-dependent degradation of various proteins has evolved into the therapeutically relevant PROTAC technology. This tethered ubiquitinylation of various targets coupled with a broad assortment of modifying E3 ubiquitin ligases has been made possible by rational design of bi-specific chimeric molecules that bring these proteins in proximity. However, forced ubiquitinylation inflicted by the binary warheads of a chimeric PROTAC molecule should not necessarily result in protein degradation but can be used to modulate other cellular functions. In this respect it should be noted that the ubiquitinylation of a diverse set of proteins is known to control their transport, transcriptional activity, and protein-protein interactions. This review provides examples of potential PROTAC usage based on non-degradable ubiquitinylation.

Mutations in fibulin-1 and collagen IV suppress the short healthspan of mig-17/ADAMTS mutants in Caenorhabditis elegans

The ADAMTS (a disintegrin and metalloprotease with thrombospondin motifs) family metalloprotease MIG-17 plays a crucial role in the migration of gonadal distal tip cells (DTCs) in Caenorhabditis elegans. MIG-17 is secreted from the body wall muscle cells and localizes to the basement membranes (BMs) of various tissues including the gonadal BM where it regulates DTC migration through its catalytic activity. Missense mutations in the BM protein genes, let-2/collagen IV a2 and fbl-1/fibulin-1, have been identified as suppressors of the gonadal defects observed in mig-17 mutants. Genetic analyses indicate that LET-2 and FBL-1 act downstream of MIG-17 to regulate DTC migration. In addition to the control of DTC migration, MIG-17 also plays a role in healthspan, but not in lifespan. Here, we examined whether let-2 and fbl-1 alleles can suppress the age-related phenotypes of mig-17 mutants. let-2(k196) fully and fbl-1(k201) partly, but not let-2(k193) and fbl-1(k206), suppressed the senescence defects of mig-17. Interestingly, fbl-1(k206), but not fbl-1(k201) or let-2 alleles, exhibited an extended lifespan compared to the wild type when combined with mig-17. These results reveal allele specific interactions between let-2 or fbl-1 and mig-17 in age-related phenotypes, indicating that basement membrane physiology plays an important role in organismal aging.

ALKBH5-mediated m6A demethylation of Runx2 mRNA promotes extracellular matrix degradation and intervertebral disc degeneration

BACKGROUND

N6-methyladenosine (m6A) methylation is a prevalent RNA modification implicated in various diseases. However, its role in intervertebral disc degeneration (IDD), a common cause of low back pain, remains unclear.

RESULTS

In this investigation, we explored the involvement of m6A demethylation in the pathogenesis of IDD. Our findings revealed that ALKBH5 (alkylated DNA repair protein AlkB homolog 5), an m6A demethylase, exhibited upregulation in degenerative discs upon mild inflammatory stimulation. ALKBH5 facilitated m6A demethylation within the three prime untranslated region (3'-UTR) of Runx2 mRNA, consequently enhancing its mRNA stability in a YTHDF1 (YTH N6-methyladenosine RNA binding protein F1)-dependent manner. The subsequent elevation in Runx2 expression instigated the upregulation of ADAMTSs and MMPs, pivotal proteases implicated in extracellular matrix (ECM) degradation and IDD progression. In murine models, subcutaneous administration of recombinant Runx2 protein proximal to the lumbar disc in mice elicited complete degradation of intervertebral discs (IVDs). Injection of recombinant MMP1a and ADAMTS10 proteins individually induced mild to moderate degeneration of the IVDs, while co-administration of MMP1a and ADAMTS10 resulted in moderate to severe degeneration. Notably, concurrent injection of the Runx2 inhibitor CADD522 with recombinant Runx2 protein did not result in IVD degeneration in mice. Furthermore, genetic knockout of ALKBH5 and overexpression of YTHDF1 in mice, along with lipopolysaccharide (LPS) treatment to induce inflammation, did not alter the expression of Runx2, MMPs, and ADAMTSs, and no degeneration of the IVDs was observed.

CONCLUSION

Our study elucidates the role of ALKBH5-mediated m6A demethylation of Runx2 mRNA in activating MMPs and ADAMTSs, thereby facilitating ECM degradation and promoting the occurrence of IDD. Our findings suggest that targeting the ALKBH5/Runx2/MMPs/ADAMTSs axis may represent a promising therapeutic strategy for preventing IDD.

Related cellular signaling and consequent pathophysiological outcomes of ubiquitin specific protease 24

Ubiquitin-specific protease 24 (USP24) is an essential member of the deubiquitinating protease family found in eukaryotes. It engages in interactions with multiple proteins, including p53, MCL-1, E2F4, and FTH1, among others. Through these interactions, USP24 plays a critical role in regulating vital cellular processes such as cell cycle control, DNA damage response, cellular iron autophagy, and apoptosis. Increased levels of USP24 have been observed in various cancer types, including bladder cancer, lung cancer, myeloma, hepatocellular carcinoma, and gastric cancer. However, in certain tumors like kidney cancer, USP24 is significantly downregulated, and the specific mechanism behind this remains unclear. Currently, there are no officially approved USP24 inhibitors available for clinical use. Some existing inhibitors targeting USP24 have shown promising effects in treating malignancies; however, their precise mode of action and information regarding binding sites are not well understood. Moreover, further optimization is required to enhance the selectivity and efficacy of these inhibitors. This review aims to provide a comprehensive overview of recent advancements in understanding the cellular functions of USP24, its association with various diseases, and the development of small-molecule inhibitors that target this protein. In conclusion, USP24 represents a promising therapeutic target for various diseases, and ongoing research will contribute to validating its role and facilitating the development of effective treatments.