A dominant mutant allele of the ING4 tumor suppressor found in human cancer cells exacerbates MYC-initiated mouse mammary tumorigenesis

Tumor immune microenvironment permissive to metastatic progression of ING4-deficient breast cancer

Deficiencies in the ING4 tumor suppressor are associated with advanced stage tumors and poor patient survival in cancer. ING4 was shown to inhibit NF-kB in several cancers. As NF-kB is a key mediator of immune response, the ING4/NF-kB axis is likely to manifest in tumor-immune modulation but has not been investigated. To characterize the tumor immune microenvironment associated with ING4-deficient tumors, three approaches were employed in this study: First, tissue microarrays composed of 246 primary breast tumors including 97 ING4-deficient tumors were evaluated for the presence of selective immune markers, CD68, CD4, CD8, and PD-1, using immunohistochemical staining. Second, an immune-competent mouse model of ING4-deficient breast cancer was devised utilizing CRISPR-mediated deletion of Ing4 in a Tp53 deletion-derived mammary tumor cell line; mammary tumors were evaluated for immune markers using flow cytometry. Lastly, the METABRIC gene expression dataset was evaluated for patient survival related to the immune markers associated with Ing4-deleted tumors. The results showed that CD68, CD4, CD8, or PD-1, was not significantly associated with ING4-deficient breast tumors, indicating no enrichment of macrophages, T cells, or exhausted T cell types. In mice, Ing4-deleted mammary tumors had a growth rate comparable to Ing4-intact tumors but showed increased tumor penetrance and metastasis. Immune marker analyses of Ing4-deleted tumors revealed a significant increase in tumor-associated macrophages (Gr-1loCD11b+F4/80+) and a decrease in granzyme B-positive (GzmB+) CD4+ T cells, indicating a suppressive and/or less tumoricidal immune microenvironment. The METABRIC data analyses showed that low expression of GZMB was significantly associated with poor patient survival, as was ING4-low expression, in the basal subtype of breast cancer. Patients with GZMB-low/ING4-low tumors had the worst survival outcomes (HR = 2.80, 95% CI 1.36-5.75, p = 0.0004), supportive of the idea that the GZMB-low immune environment contributes to ING4-deficient tumor progression. Collectively, the study results demonstrate that ING4-deficient tumors harbor a microenvironment that contributes to immune evasion and metastasis.

Inhibition of CK2/ING4 Pathway Facilitates Non-Small Cell Lung Cancer Immunotherapy

Immune cells can protect against tumor progression by killing cancer cells, while aberrant expression of the immune checkpoint protein PD-L1 (programmed death ligand 1) in cancer cells facilitates tumor immune escape and inhibits anti-tumor immunotherapy. As a serine/threonine kinase, CK2 (casein kinase 2) regulates tumor progression by multiple pathways, while it is still unclear the effect of CK2 on tumor immune escape. Here it is found that ING4 induced PD-L1 autophagic degradation and inhibites non-small cell lung cancer (NSCLC) immune escape by increasing T cell activity. However, clinical analysis suggests that high expression of CK2 correlates with low ING4 protein level in NSCLC. Further analysis shows that CK2 induce ING4-S150 phosphorylation leading to ING4 ubiquitination and degradation by JFK ubiquitin ligase. In contrast, CK2 gene knockout increases ING4 protein stability and T cell activity, subsequently, inhibites NSCLC immune escape. Furthermore, the combined CK2 inhibitor with PD-1 antibody effectively enhances antitumor immunotherapy. These findings provide a novel strategy for cancer immunotherapy.

ING Tumour Suppressors and ING Splice Variants as Coregulators of the Androgen Receptor Signalling in Prostate Cancer

Prevention and overcoming castration resistance of prostate cancer (PC) remains one of the main unsolved problems in modern oncology. Hence, many studies are focused on the investigation of novel androgen receptor (AR) regulators that could serve as potential drug targets in disease therapy. Among such factors, inhibitor of growth (ING) proteins were identified. Some ING proteins act as AR transcriptional coregulators, indicating their relevance for PC research. The ING family consists of five protein-coding genes from ING1 to ING5 and pseudogene INGX. The ING genes were revealed through their sequence homology to the first identified ING1 from an in vivo screen. ING factors are a part of histone modification complexes. With the help of the conserved plant homeodomain (PHD) motif, ING factors bind to Histone 3 Lysine 4 (H3K4) methylation mark with a stronger affinity to the highest methylation grade H3K4me3 and recruit histone acetyltransferases (HAT) and histone deacetylases (HDAC) to chromatin. ING1 and ING2 are core subunits of mSIN3a-HDAC corepressor complexes, whereas ING3–5 interact with different HAT complexes that serve as coactivators. ING members belong to type II tumour suppressors and are frequently downregulated in many types of malignancies, including PC. As the family name indicates, ING proteins are able to inhibit cell growth and tumour development via regulation of cell cycle and cancer-relevant pathways such as apoptosis, cellular senescence, DNA repair, cell migration, invasion, and angiogenesis. Many ING splice variants that enhance the diversity of ING activity were discovered. However, it seems that the existence of multiple ING splice variants is underestimated, since alternative splice variants, such as the AR coregulators ING1 and ING3, counteract full-length ING and thus play an opposite functional role. These results open a novel prospective investigation direction in understanding ING factors biology in PC and other malignancies.

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.

Proteomic analysis of the OGT interactome: novel links to epithelial-mesenchymal transition and metastasis of cervical cancer

The role of O-GlcNAc transferase (OGT) in gene regulation and tumor invasion is poorly understood. Here, we have identified several previously undiscovered OGT-interacting proteins, including the PRMT5/WDR77 complex, the PRC2 complex, the ten-eleven translocation (TET) family, the CRL4B complex and the nucleosome remodeling and deacetylase (NuRD) complex. Genome-wide analysis of target genes responsive to OGT resulted in identification of a cohort of genes including SNAI1 and ING4 that are critically involved in cell epithelial–mesenchymal transition and invasion/metastasis. We have demonstrated that OGT promotes carcinogenesis and metastasis of cervical cancer cells. OGT’s expression is significantly upregulated in cervical cancer, and low OGT level is correlated with improved prognosis. Our study has thus revealed a mechanistic link between OGT and tumor progression, providing potential prognostic indicators and targets for cancer therapy.

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.

Writing, erasing and reading histone lysine methylations

Histone modifications are key epigenetic regulatory features that have important roles in many cellular events. Lysine methylations mark various sites on the tail and globular domains of histones and their levels are precisely balanced by the action of methyltransferases ('writers') and demethylases ('erasers'). In addition, distinct effector proteins ('readers') recognize specific methyl-lysines in a manner that depends on the neighboring amino-acid sequence and methylation state. Misregulation of histone lysine methylation has been implicated in several cancers and developmental defects. Therefore, histone lysine methylation has been considered a potential therapeutic target, and clinical trials of several inhibitors of this process have shown promising results. A more detailed understanding of histone lysine methylation is necessary for elucidating complex biological processes and, ultimately, for developing and improving disease treatments. This review summarizes enzymes responsible for histone lysine methylation and demethylation and how histone lysine methylation contributes to various biological processes.

Miz1, a Novel Target of ING4, Can Drive Prostate Luminal Epithelial Cell Differentiation

BACKGROUND

How prostate epithelial cells differentiate and how dysregulation of this process contributes to prostate tumorigenesis remain unclear. We recently identified a Myc target and chromatin reader protein, ING4, as a necessary component of human prostate luminal epithelial cell differentiation, which is often lost in primary prostate tumors. Furthermore, loss of ING4 in the context of oncogenic mutations is required for prostate tumorigenesis. Identifying the gene targets of ING4 can provide insight into how its loss disrupts differentiation and leads to prostate cancer.

METHODS

Using a combination of RNA-Seq, a best candidate approach, and chromatin immunoprecipitation (ChIP), we identified Miz1 as a new ING4 target. ING4 or Miz1 overexpression, shRNA knock-down, and a Myc-binding mutant were used in a human in vitro differentiation assay to assess the role of Miz1 in luminal cell differentiation.

RESULTS

ING4 directly binds the Miz1 promoter and is required to induce Miz1 mRNA and protein expression during luminal cell differentiation. Miz1 mRNA was not induced in shING4 expressing cells or tumorigenic cells in which ING4 is not expressed. Miz1 dependency on ING4 was unique to differentiating luminal cells; Miz1 mRNA expression was not induced in basal cells. Although Miz1 is a direct target of ING4, and its overexpression can drive luminal cell differentiation, Miz1 was not required for differentiation.

CONCLUSIONS

Miz1 is a newly identified ING4-induced target gene which can drive prostate luminal epithelial cell differentiation although it is not absolutely required. Prostate 77:49-59, 2017. © 2016 Wiley Periodicals, Inc.

Tumor suppressor ING4 inhibits estrogen receptor activity in breast cancer cells

Resistance to antiestrogen therapy remains a significant problem in breast cancer. Low expression of inhibitor of growth 4 (ING4) in primary tumors has been correlated with increased rates of recurrence in estrogen receptor-positive (ER+) breast cancer patients, suggesting a role for ING4 in ER signaling. This study provides evidence that ING4 inhibits ER activity. ING4 overexpression increased the sensitivity of T47D and MCF7 ER+ breast cancer cells to hormone deprivation. ING4 attenuated maximal estrogen-dependent cell growth without affecting the dose–response of estrogen. These results indicated that ING4 functions as a noncompetitive inhibitor of estrogen signaling and may inhibit estrogen-independent ER activity. Supportive of this, treatment with fulvestrant but not tamoxifen rendered T47D cells sensitive to hormone deprivation as did ING4 overexpression. ING4 did not affect nuclear ERα protein expression, but repressed selective ER-target gene transcription. Taken together, these results demonstrated that ING4 inhibited estrogen-independent ER activity, suggesting that ING4-low breast tumors recur faster due to estrogen-independent ER activity that renders tamoxifen less effective. This study puts forth fulvestrant as a proposed therapy choice for patients with ING4-low ER+ breast tumors.

INGs are potential drug targets for cancer

PURPOSE

The inhibitor of growth (ING) family consists of ING1, ING2, ING3, ING4 and ING5, which function as the type II tumor suppressors. INGs regulate cell proliferation, senescence, apoptosis, differentiation, angiogenesis, DNA repair, metastasis, and invasion by multiple pathways. In addition, INGs increase cancer cell sensitivity for chemotherapy and radiotherapy, while clinical observations show that INGs are frequently lost in some types of cancers. The aim of the study was to summarize the recent progress regarding INGs regulating tumor progression.

METHODS

The literatures of INGs regulating tumor progression were searched and assayed.

RESULTS

The regulating signaling pathways of ING1, ING2, ING3 or ING4 on tumor progression were shown. The mechanisms of INGs on tumor suppression were also assayed.

CONCLUSIONS

This review better summarized the signaling mechanism of INGs on tumor suppression, which provides a candidate therapy strategy for cancers.

Reduced expression and prognostic implication of inhibitor of growth 4 in human osteosarcoma

Osteosarcoma is the most prevalent type of primary malignant bone tumor. Inhibitor of growth 4 (ING4) has been demonstrated to function as a tumor suppressor through multiple pathways, and is its expression is understood to be suppressed or reduced in various malignancies. The present study aimed to investigate the expression of ING4 and to determine its prognostic value in osteosarcoma tissue. Formalin-fixed, paraffin-embedded tissue microarrays were analyzed, and contained 41 osteosarcoma specimens and 11 normal bone tissue specimens with duplicate cores. ING4 expression was evaluated by immunohistochemical staining. The association between ING4 expression in the osteosarcoma and normal bone tissues was analyzed, in addition to the association between ING4 expression and Enneking classification of the osteosarcoma tissues. A significant statistical difference was observed in the ING4 immunohistochemical staining score between the osteosarcoma and normal bone tissues (P<0.001). Furthermore, a significant negative correlation was detected between the ING4 immunohistochemical staining scores and the Enneking classification results of the 41 osteosarcoma tissues (P=0.002). Low expression of ING4 was observed in the osteosarcoma specimens, and this reduced expression of ING4 was negatively correlated with Enneking classification. Thus, the results of the present study indicate that ING4 may serve as a promising prognostic marker in osteosarcoma.

Inhibitor of growth-4 is a potential target for cancer therapy

The inhibitor of growth-4 (ING-4) belongs to the inhibitor of growth (ING) family that is a type II tumor suppressor gene including five members (ING1-5). As a tumor suppressor, ING4 inhibits tumor growth, invasion, and metastasis by multiple signaling pathways. In addition to that, ING4 can facilitate cancer cell sensitivity to chemotherapy and radiotherapy. Although ING4 loss is observed for many types of cancers, increasing evidences show that ING4 can be used for gene therapy. In this review, the recent progress of ING4 regulating tumorigenesis is discussed.

SCF(JFK) is a bona fide E3 ligase for ING4 and a potent promoter of the angiogenesis and metastasis of breast cancer

The tumor suppressor ING4 (inhibitor of growth protein 4) is involved in various cellular processes by virtue of its epigenetic regulatory capability and through its positive regulation of p53 and negative regulation of NFκB. Yan et al. find that the F-box protein JFK targets ING4 for ubiquitination and degradation through assembly of an Skp1-Cul1-F-box (SCF) complex. JFK-mediated ING4 destabilization leads to the hyperactivation of the canonical NFκB pathway and promotes angiogenesis and metastasis of breast cancer.

Loss of function/dysregulation of inhibitor of growth 4 (ING4) and hyperactivation of NF-κB are frequent events in many types of human malignancies. However, the molecular mechanisms underlying these remarkable aberrations are not understood. Here, we report that ING4 is physically associated with JFK. We demonstrated that JFK targets ING4 for ubiquitination and degradation through assembly of an Skp1–Cul1–F-box (SCF) complex. We showed that JFK-mediated ING4 destabilization leads to the hyperactivation of the canonical NF-κB pathway and promotes angiogenesis and metastasis of breast cancer. Significantly, the expression of JFK is markedly up-regulated in breast cancer, and the level of JFK is negatively correlated with that of ING4 and positively correlated with an aggressive clinical behavior of breast carcinomas. Our study identified SCF^JFK as a bona fide E3 ligase for ING4 and unraveled the JFK–ING4–NF-κB axis as an important player in the development and progression of breast cancer, supporting the pursuit of JFK as a potential target for breast cancer intervention.

Stromal ING1 expression induces a secretory phenotype and correlates with breast cancer patient survival

BACKGROUND

Previous studies have established that levels of the Inhibitor of Growth 1(ING1) tumor suppressor are reduced in a significant proportion of different cancer types. Here we analyzed levels of ING1 in breast cancer patients to determine its prognostic significance as a biomarker for breast cancer prognosis.

METHODS

We used automated quantitative analysis (AQUA) to determine the levels of ING1 in the tumor associated stromal cells of 462 breast cancer samples. To better understand how high ING1 levels affect nearby epithelium, we measured the levels of cytokines and secreted matrix metalloproteases (MMPs), using an ELISA based assay in mammary fibroblasts overexpressing ING1. These cells were also used in a 3-dimensional co-culture with MCF7 cells to determine the effect of released MMPs and other cytokines on growing colonies.

RESULTS

We find that high levels of ING1 in stroma are associated with tumor grade (p = 0.001) and size (p = 0.02), and inversely associated with patient survival (p = 0.0001) in luminal, but not in non-luminal cancers, suggesting that high stromal ING1 promotes cancer development. In this group of patients ING1 could also predict patient survival and act as a biomarker (HR = 2.125). While ING1 increased or decreased the expression of different cytokines, ING1 also increased the levels of MMP1, MMP3 and MMP10 by 5-8 fold, and concomitantly decreased levels of the tissue inhibitors of metalloproteases TIMP2, TIMP3 and TIMP4 by 1.5-3.3 fold, resulting in significant increases in MMP activity as determined by zymography. Co-culturing of MCF7 cells with stromal cells expressing ING1 in 3-dimensional organoid cultures suggested that MCF7 colonies were less well defined, suggesting that secreted MMPs might promote migration.

CONCLUSION

These data indicate that stromal ING1 expression can predict the survival of patients with luminal breast cancer. High levels of ING1 in stromal cells can promote the development of breast cancer through increased expression and release of MMPs and down regulation of TIMPs, which may be an underlying mechanism of reduced patient survival.

Experimental studies on the inhibition of adenovirus-ING4-OSM therapy on nasopharyngeal carcinoma proliferation in vitro and in vivo

In the present study, the effects of the co-transfer of the tumor growth inhibitor 4 gene (ING4) together with the Oncostatin M (OSM) were investigated on tumor regression and subsequent tumor recurrence. We constructed a recombinant adenovirus carrying ING4 and OSM, which could induce high-level expression of these three genes in NPC CNE-1 cells. Ad-ING4, Ad-OSM and Ad-ING4-OSM infection all inhibited the growth of CNE-1 cells in vitro, while the Ad-ING4-OSM exerted the strongest inhibitory effect. In CNE-1 xenograft tumor models mice, an intratumoral injection of Ad-ING4, Ad-OSM and Ad-ING4-OSM resulted in a reduced tumor burden, compared to normal saline controls. Therefore, we suggested that the introduction of adenovirus-mediated ING4 and OSM genes could synergistically decrease the recurrence or metastases and develop a control of NPC tumors, which advocate a promising therapeutic future in NPC treatment.

Transient induction of ING4 by Myc drives prostate epithelial cell differentiation and its disruption drives prostate tumorigenesis

The mechanisms by which Myc overexpression or Pten loss promotes prostate cancer development are poorly understood. We identified the chromatin remodeling protein, ING4, as a crucial switch downstream of Myc and Pten that is required for human prostate epithelial differentiation. Myc-induced transient expression of ING4 is required for the differentiation of basal epithelial cells into luminal cells, while sustained ING4 expression induces apoptosis. ING4 expression is lost in >60% of human primary prostate tumors. ING4 or Pten loss prevents epithelial cell differentiation, which was necessary for tumorigenesis. Pten loss prevents differentiation by blocking ING4 expression, which is rescued by ING4 re-expression. Pten or ING4 loss generates tumor cells that co-express basal and luminal markers, indicating prostate oncogenesis occurs through disruption of an intermediate step in the prostate epithelial differentiation program. Thus, we identified a new epithelial cell differentiation switch involving Myc, Pten, and ING4, which when disrupted leads to prostate tumorigenesis. Myc overexpression and Pten loss are common genetic abnormalities in prostate cancer, whereas loss of the tumor suppressor ING4 has not been reported. This is the first demonstration that transient ING4 expression is absolutely required for epithelial differentiation, its expression is dependent on Myc and Pten, and it is lost in the majority of human prostate cancers. This is the first demonstration that loss of ING4, either directly or indirectly through loss of Pten, promotes Myc-driven oncogenesis by deregulating differentiation. The clinical implication is that Pten/ING4 negative and ING4-only negative tumors may reflect two distinct subtypes of prostate cancer.

Cancer may be a pathway to cell survival under persistent hypoxia and elevated ROS: a model for solid-cancer initiation and early development

A number of proposals have been made in the past century regarding what may drive sporadic cancers to initiate and develop. Yet the problem remains largely unsolved as none of the proposals have been widely accepted as cancer-initiation drivers. We propose here a driver model for the initiation and early development of solid cancers associated with inflammation-induced chronic hypoxia and reactive oxygen species (ROS) accumulation. The model consists of five key elements: (i)human cells tend to have a substantial gap between ATP demand and supply during chronic hypoxia, which would inevitably lead to increased uptake of glucose and accumulation of its metabolites; (ii) the accumulation of these metabolites will cast mounting pressure on the cells and ultimately result in the production and export of hyaluronic acid; (iii) the exported hyaluronic acid will be degraded into fragments of various sizes, serving as tissue-repair signals, including signals for cell proliferation, cell survival and angiogenesis, which lead to the initial proliferation of the underlying cells; (iv) cell division provides an exit for the accumulated glucose metabolites using them towards macromolecular synthesis for the new cell, and hence alleviate the pressure from the metabolite accumulation; and (v) this process continues as long as the hypoxic condition persists. In tandem, genetic mutations may be selected to make cell divisions and hence survival more sustainable and efficient, also increasingly more uncontrollable. This model also applies to some hereditary cancers as their key mutations, such as BRCA for breast cancer, generally lead to increased ROS and ultimately to repression of mitochondrial activities and up-regulation of glycolysis, as well as hypoxia; hence the energy gap, glucose-metabolite accumulation, hyaluronic acid production and continuous cell division for survival.

Keep-ING balance: tumor suppression by epigenetic regulation

Cancer cells accumulate genetic and epigenetic changes that alter gene expression to drive tumorigenesis. Epigenetic silencing of tumor suppressor, cell cycle, differentiation and DNA repair genes contributes to neoplastic transformation. The ING (inhibitor of growth) proteins (ING1-ING5) have emerged as a versatile family of growth regulators, phospholipid effectors, histone mark sensors and core components of HDAC1/2 - and several HAT chromatin-modifying complexes. This review will describe the characteristic pathways by which ING family proteins differentially affect the Hallmarks of Cancer and highlight the various epigenetic mechanisms by which they regulate gene expression. Finally, we will discuss their potentials as biomarkers and therapeutic targets in epigenetic treatment strategies.

Negative regulation of NF-κB by the ING4 tumor suppressor in breast cancer

Nuclear Factor kappa B (NF-κB) is a key mediator of normal immune response but contributes to aggressive cancer cell phenotypes when aberrantly activated. Here we present evidence that the Inhibitor of Growth 4 (ING4) tumor suppressor negatively regulates NF-κB in breast cancer. We surveyed primary breast tumor samples for ING4 protein expression using tissue microarrays and a newly generated antibody. We found that 34% of tumors expressed undetectable to low levels of the ING4 protein (n = 227). Tumors with low ING4 expression were frequently large in size, high grade, and lymph node positive, suggesting that down-regulation of ING4 may contribute to breast cancer progression. In the same tumor set, we found that low ING4 expression correlated with high levels of nuclear phosphorylated p65/RelA (p-p65), an activated form of NF-κB (p = 0.018). Fifty seven percent of ING4-low/p-p65-high tumors were lymph node-positive, indicating a high metastatic tendency of these tumors. Conversely, ectopic expression of ING4 inhibited p65/RelA phosphorylation in T47D and MCF7 breast cancer cells. In addition, ING4 suppressed PMA-induced cell invasion and NF-κB-target gene expression in T47D cells, indicating that ING4 inhibited NF-κB activity in breast cancer cells. Supportive of the ING4 function in the regulation of NF-κB-target gene expression, we found that ING4 expression levels inversely correlated with the expression of NF-κB-target genes in primary breast tumors by analyzing public gene expression datasets. Moreover, low ING4 expression or high expression of the gene signature composed of a subset of ING4-repressed NF-κB-target genes was associated with reduced disease-free survival in breast cancer patients. Taken together, we conclude that ING4 negatively regulates NF-κB in breast cancer. Consequently, down-regulation of ING4 leads to activation of NF-κB, contributing to tumor progression and reduced disease-free patient survival in breast cancer.

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.

Short-Form Ron Promotes Spontaneous Breast Cancer Metastasis through Interaction with Phosphoinositide 3-Kinase

Receptor tyrosine kinases (RTKs) have been the subject of intense investigation due to their widespread deregulation in cancer and the prospect of developing targeted therapeutics against these proteins. The Ron RTK has been implicated in tumor aggressiveness and is a developing target for therapy, but its function in tumor progression and metastasis is not fully understood. We examined Ron activity in human breast cancers and found striking predominance of an activated Ron isoform known as short-form Ron (sfRon), whose function in breast tumors has not been explored. We found that sfRon plays a significant role in aggressiveness of breast cancer in vitro and in vivo. sfRon expression was sufficient to convert slow-growing, nonmetastatic tumors into rapidly growing tumors that spontaneously metastasized to liver and bones. Mechanistic studies revealed that sfRon promotes epithelial-mesenchymal transition, invasion, tumor growth, and metastasis through interaction with p85, the regulatory subunit of phosphoinositide 3-kinase (PI3K). Inhibition of PI3K activity, or introduction of a single mutation in the p85 docking site on sfRon, completely eliminated the ability of sfRon to promote tumor growth, invasion, and metastasis. These findings reveal sfRon as an important new player in breast cancer and validate Ron and PI3K as therapeutic targets in this disease.

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.

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

Inhibitor of growth 4 (ING4) is a member of the ING family of tumor suppressor proteins. In this study, we have analyzed the impact of two mutations in ING4 associated with human tumors (Y121N and N214D), testing their behavior in a series of functional, biochemical and structural analyses. We report that the N214D mutation dramatically dampened the ability of ING4 to inhibit proliferation, anchorage-independent growth or cell migration or to sensitize to cell death. In turn, the Y121N mutant did not differ significantly from wild-type ING4 in our assays. Neither of the mutations altered the normal subcellular localization of ING4, showing predominantly nuclear accumulation. We investigated the molecular basis of the defect in the activity of the N214D mutant. The folding and ability to bind histone marks of ING4 was not significantly altered by this mutation. Instead, we found that the functional impairment of the N214D mutant correlates with reduced protein stability due to increased proteasome-mediated degradation. In summary, our data demonstrates that a point mutation of ING4 associated to human tumors leads to the loss of several essential functions of ING4 pertinent to tumor protection and highlight the importance of ING4 function to prevent tumorigenesis.