Yonghwan Shin

Background and Aims: Thermal ablation is the standard-of-care treatment modality with curative intent for early-stage nonresectable HCC, but a durable response is limited, with up to 40% of patients with HCC eventually experiencing local recurrence on posttreatment surveillance. While thermal ablation has been established to cause immediate cell death in the center of the thermal ablation zone, its metabolic impact in the peri-ablational region remains unclear. We aimed to elucidate the metabolic mechanism by which Galectin-1 (Gal-1) promotes thermal-ablation–induced hyperthermia resistance in HCC and demonstrate the therapeutic potential of inhibiting Gal-1 in combination with thermal ablation in vivo . Approach and Results: Proteomic analysis was performed using an untargeted approach on pre-ablation formalin-fixed paraffin-embedded biopsy specimens of thermal ablation responders (n=32) and nonresponders (n=23). Gal-1 was found to be overexpressed in thermal ablation nonresponders compared with responders. Moreover, HCC with Gal-1 overexpression demonstrated reduced sensitivity to hyperthermia in vitro and increased utilization of glycolysis and the downstream tricarboxylic acid (TCA) cycle under hyperthermia-induced stress. Gal-1–overexpressing HCC enhanced its metabolic utilization through Gal-1–facilitated GM1-ganglioside breakdown, producing galactose to increase the metabolic influxes into glycolysis and consequently the downstream TCA cycle. In-vivo studies showed that inhibiting Gal-1 in combination with thermal ablation significantly reduced tumor size compared with either monotherapy thermal ablation or Gal-1 inhibition alone. Conclusions: Gal-1 can mediate hyperthermia resistance in HCC and can potentially be modulated as a therapeutic target to reduce rapid progression after thermal ablation.

Histones are essential for DNA packaging and undergo post-translational modifications that significantly influence gene regulation. Among these modifications, histone tail cleavage has recently garnered attention despite being less explored. Cleavage by various proteases impacts processes such as stem cell differentiation, aging, infection, and inflammation, though the mechanisms remain unclear. This review delves into recent insights on histone proteolytic cleavage and its epigenetic significance, highlighting how chromatin, which serves as a dynamic scaffold, responds to signals through histone modification, replacement, and ATP-dependent remodeling. Specifically, histone tail cleavage is linked to critical cellular processes such as granulocyte differentiation, viral infection, aging, yeast sporulation, and cancer development. Although the exact mechanisms connecting histone cleavage to gene expression are still emerging, it is clear that this process represents a novel epigenetic transcriptional mechanism intertwined with chromatin dynamics. This review explores known histone tail cleavage events, the proteolytic enzymes involved, their impact on gene expression, and future research directions in this evolving field.

The interwoven relationship between gut microbiota and the epigenetic landscape constitutes a pivotal axis in understanding human health and disease. Governed by a myriad of dietary, genetic, and environmental influences, the gut microbiota orchestrates a sophisticated metabolic interplay, shaping nutrient utilization, immune responses, and defenses against pathogens. Recent strides in genomics and metabolomics have shed light on the intricate connections between these microbial influencers and the host’s physiological dynamics, presenting a dynamic panorama across diverse disease spectra. DNA methylation and histone modifications, as key players in epigenetics, intricately align with the dynamic orchestration of the gut microbiota. This seamless collaboration, notably evident in conditions like inflammatory bowel disease and obesity, has captured the attention of researchers, prompting an exploration of its nuanced choreography. Nevertheless, challenges abound. Analyzing data is intricate due to the multifaceted nature of the gut microbiota and the limitations of current analytical methods. This underscores the need for a multidisciplinary approach, where diverse disciplines converge to pave innovative research pathways. The integration of insights from microbiome and epigenome studies assumes paramount importance in unraveling the complexities of this intricate partnership. Deciphering the synchronized interactions within this collaboration offers a deeper understanding of these delicate interplays, potentially heralding revolutionary strides in treatment modalities and strategies for enhancing public health.

Vpr binding protein (VprBP), also known as DDB1- and CUL4-associated factor1 (DCAF1), is a recently identified atypical kinase and plays an important role in downregulating the transcription of tumor suppressor genes as well as increasing the risk for colon and prostate cancers. Melanoma is the most aggressive form of skin cancer arising from pigment-producing melanocytes and is often associated with the dysregulation of epigenetic factors targeting histones. Here, we demonstrate that VprBP is highly expressed and phosphorylates threonine 120 (T120) on histone H2A to drive the transcriptional inactivation of growth-regulatory genes in melanoma cells. As is the case for its epigenetic function in other types of cancers, VprBP acts to induce a gene silencing program dependent on H2AT120 phosphorylation (H2AT120p). The significance of VprBP-mediated H2AT120p is further underscored by the fact that VprBP knockdown- or VprBP inhibitor-induced lockage of H2AT120p mitigates melanoma tumor growth in xenograft models. Collectively, our results establish VprBP-mediated H2AT120p as a key epigenetic signal for melanomagenesis and suggest the therapeutic potential of targeting VprBP kinase activity for effective melanoma treatment.

VprBP (also known as DCAF1) is a recently identified kinase that is overexpressed in cancer cells and serves as a major determinant for epigenetic gene silencing and tumorigenesis. The role of VprBP in driving target gene inactivation has been largely attributed to its ability to mediate histone H2A phosphorylation. However, whether VprBP also phosphorylates non-histone proteins and whether these phosphorylation events drive oncogenic signaling pathways have not been explored. Here we report that serine 367 phosphorylation (S367p) of p53 by VprBP is a key player in attenuating p53 transcriptional and growth suppressive activities. VprBP catalyzes p53S367p through a direct interaction with the C-terminal domain of p53. Mechanistically, VprBP-mediated S367p inhibits p53 function in the wake of promoting p53 proteasomal degradation, because blocking p53S367p increases p53 protein levels, thereby enhancing p53 transactivation. Furthermore, abrogation of VprBP-p53 interaction by p53 acetylation is critical for preventing p53S367p and potentiating p53 function in response to DNA damage. Together, our findings establish VprBP-mediated S367p as a negative regulator of p53 function and identify a previously uncharacterized mechanism by which S367p modulates p53 stability.

Melanoma is a type of skin cancer that develops in pigment-producing melanocytes and often spreads to other parts of the body. Aberrant gene expression has been considered as a crucial step for increasing the risk of melanomagenesis, but how chromatin reorganization contributes to this pathogenic process is still not well understood. Here we report that matrix metalloproteinase 9 (MMP-9) localizes to the nucleus of melanoma cells and potentiates gene expression by proteolytically clipping the histone H3 N-terminal tail (H3NT). From genome-wide studies, we discovered that growth-regulatory genes are selectively targeted and activated by MMP-9-dependent H3NT proteolysis in melanoma cells. MMP-9 cooperates functionally with p300/CBP because MMP-9 cleaves H3NT in a manner that is dependent on p300/CBP-mediated acetylation of H3K18. The functional significance of MMP-9-dependent H3NT proteolysis is further underscored by the fact that RNAi knockdown and small-molecule inhibition of MMP-9 and p300/CBP impede melanomagenic gene expression and melanoma tumor growth. Together, our data establish new functions and mechanisms for nuclear MMP-9 in promoting melanomagenesis and demonstrate how MMP-9-dependent H3NT proteolysis can be exploited to prevent and treat melanoma skin cancer.

Cystic fibrosis transmembrane conductance regulator (CFTR), a cyclic AMP (cAMP)-regulated chloride channel, is critical for secretion and absorption across diverse epithelia. Mutations or absence of CFTR result in pathogeneses, including cancer. While CFTR has been proposed as a tumor suppressing gene in tumors of the intestine, lung, and breast cancers, its effects in head and neck cancer (HNC) have yet to be investigated. This study aimed to define expression patterns and epigenetic modifications of CFTR in HNC. CFTR was expressed in normal but not in HNC cells and tissues. Treatment with 5-aza-2′-deoxycytidine (5-Aza-CdR) was associated with rescued expression of CFTR, whose function was confirmed by patch clamp technique. Further experiments demonstrated that CFTR CpG islands were hypermethylated in cancer cells and tissues and hypomethylated in normal cells and tissue. Our results suggest that CFTR epigenetic modifications are critical in both down-regulation and up-regulation of CFTR expression in HNC and normal cells respectively. We then investigated the impact of CFTR on expressions and functions of cancer-related genes. CFTR silencing was closely associated with changes to other cancer-related genes, suppressing apoptosis while enhancing proliferation, cell motility, and invasion in HNC. Our findings demonstrate that hypermethylation of CFTR CpG islands and CFTR deficiency is closely related to HNC.

Anoctamin1 (ANO1), a calcium activated chloride channel, is known to play a critical role in salivary secretion. In the salivary gland, ANO1 is expressed exclusively in the acinar cells, with no expression in the ductal cells. However, the mechanisms that determine this distinctive cell type-dependent expression pattern of ANO1 remain unknown. In this study, we discovered that the cell-dependent expression of ANO1 during salivary gland organogenesis is regulated by DNA methylation of ANO1 CpG islands. ANO1 CpG islands in e12 embryonic submandibular glands (eSMG) are highly methylated, but those in e14 eSMG or adult SMG are significantly unmethylated. The differential expression pattern of ANO1 in duct and acini is defined at e14. Artificial demethylation by treatment with the demethylating agent 5-aza-2’-deoxycytidine (5-Aza-CdR), induced the expression of ANO1 in both the ductal cell line Human Submandibular Gland (HSG) and in the duct cells of adult mouse SMG. During the trans-differentiation in Matrigel of duct-origin HSG cells into acinar-like phenotype, significant demethylation of ANO1 CpG islands is observed. This may be due to the reduced expression of DNA methyltransferase (DNMT) 3a and 3b. These results suggest that the differential expression of ANO1 in salivary glands during organogenesis and differentiation is mainly regulated by epigenetic demethylation of the ANO1 gene.

MMP-9-dependent proteolysis of histone H3 N-terminal tail (H3NT) is an important mechanism for activation of gene expression during osteoclast differentiation. Like other enzymes targeting their substrates within chromatin structure, MMP-9 enzymatic activity toward H3NT is tightly controlled by histone modifications such as H3K18 acetylation (H3K18ac) and H3K27 monomethylation (H3K27me1). Growing evidence indicates that DNA methylation is another epigenetic mechanism controlling osteoclastogenesis, but whether DNA methylation is also critical for regulating MMP-9-dependent H3NT proteolysis and gene expression remains unknown. We show here that treating RANKL-induced osteoclast progenitor (OCP) cells with the DNMT inhibitor 5-Aza-2′-deoxycytidine (5-Aza-CdR) induces CpG island hypomethylation and facilitates MMP-9 transcription. This increase in MMP-9 expression results in a significant enhancement of H3NT proteolysis and OCP cell differentiation. On the other hand, despite an increase in levels of H3K18ac, treatment with the HDAC inhibitor trichostatin A (TSA) leads to impairment of osteoclastogenic gene expression. Mechanistically, TSA treatment of OCP-induced cells stimulates H3K27ac with accompanying reduction in H3K27me1, which is a key modification to facilitate stable interaction of MMP-9 with nucleosomes for H3NT proteolysis. Moreover, hypomethylated osteoclastogenic genes in 5-Aza-CdR-treated cells remain transcriptionally inactive after TSA treatment, because H3K27 is highly acetylated and cannot be modified by G9a. These findings clearly indicate that DNA methylation and histone modification are important mechanisms in regulating osteoclastogenic gene expression and that their inhibitors can be used as potential therapeutic tools for treating bone disorders.

MMP-9 plays a direct role in the activation of pro-osteoclastogenic genes by cleaving histone H3N-terminal tail (H3NT) and altering chromatin architecture. Although H3 acetylation at K18 has been shown to stimulate MMP-9 enzymatic activity toward H3NT, nothing is known about the influence of other H3NT modifications on this epigenetic reaction. We show that H3 monomethylation at lysine 27 (H3K27me1) is essential for MMP-9-dependent H3NT proteolysis during RANKL-induced osteoclast differentiation. Through the recognition of H3K27me1 mark, MMP-9 localizes and generates H3NT proteolysis at the genes encoding osteoclast differentiation factors. By using RNAi and small molecule inhibitor approaches, we also confirmed that G9a is the major methyltransferase to catalyze H3K27me1 for MMP-9-dependent H3NT proteolysis and trigger the expression of osteoclast-specific genes. Our data establish new functions for G9a-mediated H3K27me1 in MMP-9-dependent H3NT proteolysis and demonstrate how histone modification can be exploited to regulate osteoclastogenic gene expression at the molecular level. Further studies are warranted to investigate the detailed mechanism by which G9a overexpression with concomitant dysregulation of osteoclastogenesis contributes to the pathogenesis of bone disorders.