Functional impact of cancer-associated mutations in the tumor suppressor protein ING4

In silico analysis prediction of HepTH1-5 as a potential therapeutic agent by targeting tumour suppressor protein networks

Many studies reported that the activation of tumour suppressor protein, p53 induced the human hepcidin expression. However, its expression decreased when p53 was silenced in human hepatoma cells. Contrary to Tilapia hepcidin TH1-5, HepTH1-5 was previously reported to trigger the p53 activation through the molecular docking approach. The INhibitor of Growth (ING) family members are also shown to directly interact with p53 and promote cell cycle arrest, senescence, apoptosis and participate in DNA replication and DNA damage responses to suppress the tumour initiation and progression. However, the interrelation between INGs and HepTH1-5 remains unknown. Therefore, this study aims to identify the mechanism and their protein interactions using in silico approaches. The finding revealed that HepTH1-5 and its ligands had interacted mostly on hotspot residues of ING proteins which involved in histone modifications via acetylation, phosphorylation, and methylation. This proves that HepTH1-5 might implicate in an apoptosis signalling pathway and preserve the protein structure and function of INGs by reducing the perturbation of histone binding upon oxidative stress response. This study would provide theoretical guidance for the design and experimental studies to decipher the role of HepTH1-5 as a potential therapeutic agent for cancer therapy. Communicated by Ramaswamy H. Sarma.

Roles of the tumor suppressor inhibitor of growth family member 4 (ING4) in cancer

Inhibitor of growth family member 4 (ING4) is best known as a tumor suppressor that is frequently downregulated, deleted, or mutated in many cancers. ING4 regulates a broad array of tumor-related processes including proliferation, apoptosis, migration, autophagy, invasion, angiogenesis, DNA repair and chromatin remodeling. ING4 alters local chromatin structure by functioning as an epigenetic reader of H3K4 trimethylation histone marks (H3K4Me3) and regulating gene transcription through directing histone acetyltransferase (HAT) and histone deacetylase (HDAC) protein complexes. ING4 may serve as a useful prognostic biomarker for many cancer types and help guide treatment decisions. This review provides an overview of ING4's central functions in gene expression and summarizes current literature on the role of ING4 in cancer and its possible use in therapy.

Deciphering structure, function and mechanism of lysine acetyltransferase HBO1 in protein acetylation, transcription regulation, DNA replication and its oncogenic properties in cancer

HBO1 complexes are major acetyltransferase responsible for histone H4 acetylation in vivo, which belongs to the MYST family. As the core catalytic subunit, HBO1 consists of an N-terminal domain and a C-terminal MYST domain that are in charge of acetyl-CoA binding and acetylation reaction. HBO1 complexes are multimeric and normally consist of two native subunits MEAF6, ING4 or ING5 and two kinds of cofactors as chromatin reader: Jade-1/2/3 and BRPF1/2/3. The choices of subunits to form the HBO1 complexes provide a regulatory switch to potentiate its activity between histone H4 and H3 tails. Thus, HBO1 complexes present multiple functions in histone acetylation, gene transcription, DNA replication, protein ubiquitination, and immune regulation, etc. HBO1 is a co-activator for CDT1 to facilitate chromatin loading of MCM complexes and promotes DNA replication licensing. This process is regulated by mitotic kinases such as CDK1 and PLK1 by phosphorylating HBO1 and modulating its acetyltransferase activity, therefore, connecting histone acetylation to regulations of cell cycle and DNA replication. In addition, both gene amplification and protein overexpression of HBO1 confirmed its oncogenic role in cancers. In this paper, we review the recent advances and discuss our understanding of the multiple functions, activity regulation, and disease relationship of HBO1.

Identification of the inhibitor of growth protein 4 (ING4) as a potential target in prostate cancer therapy

INhibitor of Growth protein 4 (ING4) is a potential chromatin modifier that has been implicated in several cancer-related processes. However, the role of ING4 in prostate cancer (PC) is largely unknown. This study aimed to assess ING4's role in global transcriptional regulation in PC cells to identify potential cellular processes associated with ING4 loss. RNA-Seq using next-generation sequencing (NGS) was used to identify altered genes in LNCaP PC cells following ING4 depletion. Ingenuity pathways analysis (IPA^®) was applied to the data to highlight candidates, ING4-regulated pathways, networks and cellular processes. Selected genes were validated using RT-qPCR. RNA-Seq of LNCaP cells revealed a total of 159 differentially expressed genes (fold change ≥ 1.5 or ≤ - 1.5, FDR ≤ 0.05) following ING4 knockdown. RT-qPCR used to validate the expression level of selected genes was in agreement with RNA-Seq results. Key genes, unique pathways, and biological networks were identified using IPA^® analysis. This is the first report of global gene regulation in PC cells by ING4. The resultant differential expression profile revealed the potential role of ING4 in PC pathogenesis possibly through modulation of key genes, pathways and biological networks that are central drivers of the disease. Collectively, these findings shed light on a novel transcriptional regulator of PC that ultimately may influence the disease progression and as a potential target in the disease therapy.

Inhibitor of growth 4 affects hypoxia-induced migration and angiogenesis regulation in retinal pigment epithelial cells

Inhibitor of growth 4 (ING4), a potential tumor suppressor, is implicated in cell migration and angiogenesis. However, its effects on diabetic retinopathy (DR) have not been elucidated. In this study, we aimed to evaluate ING4 expression in normal and diabetic rats and clarify its effects on hypoxia-induced dysfunction in human retinal pigment epithelial (ARPE-19) cells. A Type 1 diabetic model was generated by injecting rats intraperitoneally with streptozotocin and then killed them 4, 8, or 12 weeks later. ING4 expression in retinal tissue was detected using western blot analysis, reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR), and immunohistochemistry assays. After transfection with an ING4 overexpression lentiviral vector or small interfering RNA (siRNA), ARPE-19 migration under hypoxia was tested using wound healing and transwell assays. The angiogenic effect of conditioned medium (CM) from ARPE-19 cells was examined by assessing human retinal endothelial cell (HREC) capillary tube formation. Additionally, western blot analysis and RT-qPCR were performed to investigate the signaling pathways in which ING4, specificity protein 1 (Sp1), matrix metalloproteinase 2 (MMP-2), MMP-9, and vascular endothelial growth factor A (VEGF-A) were involved. Here, we found that ING4 expression was significantly reduced in the diabetic rats' retinal tissue. Silencing ING4 aggravated hypoxia-induced ARPE-19 cell migration. CM collected from ING4 siRNA-transfected ARPE-19 cells under hypoxia promoted HREC angiogenesis. These effects were reversed by ING4 overexpression. Furthermore, ING4 suppressed MMP-2, MMP-9, and VEGF-A expression in an Sp1-dependent manner in hypoxia-conditioned ARPE-19 cells. Overall, our results provide valuable mechanistic insights into the protective effects of ING4 on hypoxia-induced migration and angiogenesis regulation in ARPE-19 cells. Restoring ING4 may be a novel strategy for treating DR.

The Biological and Clinical Relevance of Inhibitor of Growth (ING) Genes in Non-Small Cell Lung Cancer

Carcinogenic mutations allow cells to escape governing mechanisms that commonly inhibit uncontrolled cell proliferation and maintain tightly regulated homeostasis between cell death and survival. Members of the inhibition of growth (ING) family act as tumor suppressors, governing cell cycle, apoptosis and cellular senescence. The molecular mechanism of action of ING genes, as well as their anchor points in pathways commonly linked to malignant transformation of cells, have been studied with respect to a variety of cancer specimens. This review of the current literature focuses specifically on the action mode of ING family members in lung cancer. We have summarized data from in vitro and in vivo studies, highlighting the effects of varying levels of ING expression in cancer cells. Based on the increasing insight into the function of these proteins, the use of ING family members as clinically useful biomarkers for lung cancer detection and prognosis will probably become routine in everyday clinical practice.

The essential role of tumor suppressor gene ING4 in various human cancers and non-neoplastic disorders

Inhibitor of growth 4 (ING4), a member of the ING family discovered in 2003, has been shown to act as a tumor suppressor and is frequently down-regulated in various human cancers. Numerous published in vivo and in vitro studies have shown that ING4 is responsible for important cancer hallmarks such as pathologic cell cycle arrest, apoptosis, autophagy, contact inhibition, and hypoxic adaptation, and also affects tumor angiogenesis, invasion, and metastasis. These characteristics are typically associated with regulation through chromatin acetylation by binding histone H3 trimethylated at lysine 4 (H3K4me3) and through transcriptional activity of transcription factor P53 and NF-κB. In addition, emerging evidence has indicated that abnormalities in ING4 expression and function play key roles in non-neoplastic disorders. Here, we provide an overview of ING4-modulated chromosome remodeling and transcriptional function, as well as the functional consequences of different genetic variants. We also present the current understanding concerning the role of ING4 in the development of neoplastic and non-neoplastic diseases. These studies offer inspiration for pursuing novel therapeutics for various cancers.

Overexpression of Inhibitor of Growth 4 Enhances Radiosensitivity in Non-Small Cell Lung Cancer Cell Line SPC-A1

Inhibitor of growth 4 is a member of the inhibitor of growth family proteins, which is involved in cell apoptosis, migration, invasion, and cell cycle progress. In this study, we investigated the inhibitor of growth 4 level in non-small cell lung cancer tissues and explored the antitumor activity of inhibitor of growth 4 in vitro and in vivo using non-small cell lung cancer cell line SPC-A1 and its underlying molecular mechanisms. We also explored its role on the radiosensitivity in SPC-A1 cells. The level of inhibitor of growth 4 protein was significantly decreased in 28 cases of non-small cell lung cancer tissues in comparison with corresponding noncancerous lung epithelial tissues. Upregulation of inhibitor of growth 4 by plasmid pcDNA3.1-ING4 delivery could suppress proliferation and increase apoptosis of SPC-A1 cells both in vitro and in vivo. Additionally, we found that overexpression of inhibitor of growth 4 in SPC-A1 cell line could lead to a higher Bcl-2/Bax ratio, which might be an important factor in the apoptosis regulation. Furthermore, overexpression of inhibitor of growth 4 enhanced the radiosensitivity of SPC-A1 cells to irradiation. Inhibitor of growth 4 upregulation plus radiotherapy induced synergistic tumor suppression in SPC-A1 xenografts implanted in athymic nude mice. Thus, the restoration of inhibitor of growth 4 function might provide a potential strategy for non-small cell lung cancer radiosensitization.

ING4 regulates JWA in angiogenesis and their prognostic value in melanoma patients

Background:

We previously showed that inhibitor of growth family member 4 (ING4) inhibits melanoma angiogenesis, and JWA suppresses the metastasis of melanoma cells. As angiogenesis is essential for tumour metastasis, further investigation of the function of ING4 and JWA in melanoma angiogenesis is needed, and their prognostic value are of great interest.

Methods:

Western blot, tube-formation assays and luciferase assays were used to investigate the correlation between ING4 and JWA in melanoma angiogenesis. JWA and integrin-linked kinase (ILK) expression was determined on a tissue microarray constructed from 175 biopsies.

Results:

ING4 promoted JWA expression by activating JWA promoter. Furthermore, the regulation of growth and tube formation of endothelial cells by ING4 was partially JWA dependent. Also, ING4 inhibited the ILK-induced angiogenesis signalling pathway via JWA. Moreover, reduced JWA, or increased ILK, expression was closely associated with 5-year disease-specific survival of melanoma patients (P=0.001 and 0.007, respectively). There was also a positive correlation between ING4 and JWA yet a negative correlation between ING4 and ILK. Importantly, their concomitant expressions were significantly related to 5-year survival of melanoma patients (P=0.002 and 0.003, respectively).

Conclusion:

JWA has an important role in ING4-regulated melanoma angiogenesis, and ING4/JWA/ILK are promising prognostic markers and may be used as anti-angiogenic therapeutic targets for melanoma.

ING4 regulates a secretory phenotype in primary fibroblasts with dual effects on cell proliferation and tumor growth

ING proteins have an essential role in the control of a variety of cellular functions whose deregulation is associated with tumor formation and dissemination, such as proliferation, apoptosis, senescence or invasion. Accordingly, loss of function of ING proteins is a frequent event in many types of human tumors. In this report, we have studied the function of ING4, a member of the ING family of tumor suppressors, in the context of normal, non-transformed primary fibroblasts. We show that ING4 negatively regulates cell proliferation in this cell type. The antiproliferative action of ING4 requires its ability to recognize chromatin marks, it is p53-dependent at least in part, and it is lost in an ING4 cancer-associated mutant. Gene expression analysis shows that ING4 regulates the expression and release of soluble factors of the chemokine family. The secretory phenotype regulated by ING4 in primary fibroblasts displays a selective paracrine effect on proliferation, fostering the division of tumor cells, while inhibiting division in primary fibroblasts. Consistently, ING4-expressing fibroblasts promoted tumor growth in vivo in co-injection tumorigenesis assays. Collectively, our results show that ING4 not only can regulate the proliferation of primary non-transformed human fibroblasts, but also orchestrates a secretory phenotype in these cells that promotes tumor cell proliferation in vitro and in vivo. These findings support a critical role for ING4 expression in normal cells in the non-cell-autonomous regulation of tumor growth.

Regulation of p53 by ING family members in suppression of tumor initiation and progression

The INhibitor of Growth (ING) family is an evolutionarily conserved set of proteins, implicated in suppression of initiation and progression of cancers in various tissues. They promote cell cycle arrest, cellular senescence and apoptosis, participate in stress responses, regulate DNA replication and DNA damage responses, and inhibit cancer cell migration, invasion, and angiogenesis of the tumors. At the molecular level, ING proteins are believed to participate in chromatin remodeling and transcriptional regulation of their target genes. However, the best known function of ING proteins is their cooperation with p53 tumor suppressor protein in tumor suppression. All major isoforms of ING family members can promote the transactivition of p53 and the majority of them are shown to directly interact with p53. In addition, ING proteins are thought to interact with and modulate the function of auxiliary members of p53 pathway, such as MDM2, ARF , p300, and p21, indicating their widespread involvement in the regulation and function of this prominent tumor suppressor pathway. It seems that p53 pathway is the main mechanism by which ING proteins exert their functions. Nevertheless, regulation of other pathways which are not relevant to p53, yet important for tumorigenesis such as TGF-β and NF-κB, by ING proteins is also observed. This review summarizes the current understanding of the mutual interactions and cooperation between different members of ING family with p53 pathway and implications of this cooperation in the suppression of cancer initiation and progression.

Effect of the tumor suppressor gene ING4 on the proliferation of MCF-7 human breast cancer cells

Inhibitor of growth 4 (ING4) is a member of the ING family and acts as a tumor suppressor protein. To investigate the impact of ING4 on breast cancer proliferation, the present study examined the antitumor effects caused by upregulation in the expression of ING4 and its possible mechanism of effect in MCF-7 cells. A plasmid-based expression system encoding the ING4 gene was used to construct a stable cell line and overexpress ING4 in MCF-7 cells. Real-time PCR and western blot analysis were used to detect the mRNA and protein expression levels of ING4, respectively. Cell growth was examined by methylthiazolyltetrazolium (MTT) assay. Cell cycle distribution and cell apoptosis were measured by flow cytometry. The expression of p21, p53 and bax genes were tested by real-time PCR and western blot analysis. The stably transfected cell lines pcDNA3.1(+)/ING4 (with the ING4 gene) and pcDNA3.1(+) (an empty vector) were established. The expression levels of ING4 mRNA and protein in the stable cell line expressing pcDNA3.1(+)/ING4 were significantly higher than those of the two control cell lines. The cell proliferation of stably transfected cells was inhibited, and the inhibitory rate was 62.58±2.93%. Based on the changes in cell cycle distribution in stably transfected cells compared with two control cell lines, a number of cells were blocked in the G0/G1 phase 67.82±3.78% (P<0.05). In addition, the apoptotic rate was significantly higher, at 31.51±3.02% (P<0.05). Real-time PCR revealed that p21 and bax mRNA expression were increased (P<0.01), but the expression of p53 did not change significantly (P>0.05) in the stably transfected cell lines. Western blot analysis results of p21, bax and p53 were in accordance with real-time PCR results. ING4 upregulation may inhibit breast cancer cell proliferation and accelerate the process of apoptosis. It is suggested that ING4 plays a significant role in the suppression of breast cancer progression.

Crystal structure of inhibitor of growth 4 (ING4) dimerization domain reveals functional organization of ING family of chromatin-binding proteins

The protein ING4 binds to histone H3 trimethylated at Lys-4 (H3K4me3) through its C-terminal plant homeodomain, thus recruiting the HBO1 histone acetyltransferase complex to target promoters. The structure of the plant homeodomain finger bound to an H3K4me3 peptide has been described, as well as the disorder and flexibility in the ING4 central region. We report the crystal structure of the ING4 N-terminal domain, which shows an antiparallel coiled-coil homodimer with each protomer folded into a helix-loop-helix structure. This arrangement suggests that ING4 can bind simultaneously two histone tails on the same or different nucleosomes. Dimerization has a direct impact on ING4 tumor suppressor activity because monomeric mutants lose the ability to induce apoptosis after genotoxic stress. Homology modeling based on the ING4 structure suggests that other ING dimers may also exist.

Expression of tumor suppressor gene ING4 in ovarian carcinoma is correlated with microvessel density

PURPOSE

Angiogenesis, estimated by microvessel density (MVD), has been shown to predict poor progression-free survival in women with advanced epithelial ovarian cancer. Inhibitor of growth (ING) family proteins inhibit angiogenesis in a number of cancers. We evaluated the role of ING4 in regulation of angiogenesis in patients with epithelial ovarian cancer.

METHODS

Semi-quantitative RT-PCR was used to determine ING4 mRNA levels in 40 ovarian cancer patients and 40 normal controls. Also, we used immunohistochemistry to evaluate (1) ING4 protein expression levels and (2) the level of MVD by staining CD34, a microvessel marker, in these patients. Through statistical analysis, the possible correlation between the ING4 expression and angiogenesis was explored.

RESULTS

ING4 mRNA and protein were significantly downregulated in all ovarian cancer patients compared to normal controls (P < 0.001). Endometrioid carcinoma tissue had significantly lower ING4 levels compared to serous or mucinous ovarian cancer. ING4 expression correlated negatively with stage and histological grade of ovarian cancers. MVD correlated negatively with ING4 protein and mRNA levels (ρ = -0.865; P < 0.001 and ρ = -0.724; P < 0.001, respectively).

CONCLUSIONS

Loss of ING4 may promote microvessel formation and plays a role in facilitating the development of ovarian cancer. Although the specific mechanisms are not yet understood, our data suggest that ING4 may be a promising target for the treatment for ovarian cancer.

Inhibitor of growth-4 mediates chromatin modification and has a suppressive effect on tumorigenesis and innate immunity

Inhibitor of growth-4 (ING4) is a member of the ING family and acts as a tumor suppressor protein. ING4 is a promising candidate for cancer research due to its anti-angiogenic function and its role in the inhibition of cell migration, cell cycle, and induction of apoptosis. Interaction of this protein with the histone acetyl transferase complex plays a vital role in the regulation of multiple nuclear factor kappa light chain enhancer of activated B cells response elements and thus in the regulation of innate immunity. Splice variants of ING4 have different binding affinities to target sites, which results in the enhancement of its functional diversity. ING4 is among the few known regulatory proteins that can directly interact with chromatin as well as with transcription factors. The influence of ING4 on tumor necrosis factor-α, keratinocyte chemoattractant, interleukin (IL)-6, IL-8, matrix metalloproteinases, cyclooxygenase-2, and IκBα expression clearly demonstrates its critical role in the regulation of inflammatory mediators. Its interaction with liprin α1 and p53 contribute to mitigate cell spreading and induce apoptosis of cancer cells. Multiple factors including breast cancer melanoma suppressor-1 are upstream regulators of ING4 and are frequently deactivated in tumor cells. In the present review, the different properties of ING4 are discussed, and its activities are correlated with different aspects of cell physiology. Special emphasis is placed on our current understanding of ING4 with respect to its influence on chromatin modification, tumorigenesis, and innate immunity.