Genetic alterations and expression of inhibitor of growth 1 in human sporadic colorectal cancer

Molecular mechanisms of inhibitor of growth (ING) family members in health and malignancy

ING genes belong to family of tumor suppressor genes with regulatory functions on cell proliferation, apoptosis, and cellular senescence. These include a family of proteins with 5 members (ING1-5), which are downregulated in human malignancies and/or affected by pathogenic mutations. ING proteins are highly evolutionarily conserved proteins containing several domains through which bind to chromatin structures by exerting their effects as readers of histone modification marks, and also binding to proteins like p53 involved in biological processes such as cell cycle regulation. Further, they are known as subunits of histone acetylation as well as deacetylation complexes and so exert their regulatory roles through epigenetic mechanisms. Playing role in restriction of proliferative but also invasive potentials of normal cells, INGs are particularly involved in cancer development and progression. However, additional studies and experimental confirmation are required for these models. This paper highlights the potential impact that INGs may have on the development of human cancer and explores what new information has recently arise on the functions of ING genes.

mRNA and protein of p33ING1 in normal and cancer tissues

Background

Inhibitor growth protein 1 (ING1) is a tumor suppressor, and its down-regulation is involved in the progression and aggressive phenotypes of human malignancies through its interactions with the H3K4me3 and p53.

Methods

We collected datasets to analyze the relationship between ING1b mRNA expression and accumulative survival rate, and carried out immunohistochemistry analyses to determine the expression profiles of the p33ING1 protein on the mouse, normal human, and human cancer tissue microarrays.

Results

Compared with normal tissues, the ING1b mRNA was highly expressed in various types of cancer tissues, including, colorectal, lung, and breast cancers, and was positively correlated with the overall survival rate of gastric cancer patients. In mouse tissues, the subcellular location of p33ING1 was frequently nuclear; however, it was occasionally cytoplasmic or nucleocytoplasmic. There was a positive detection in the neuron body, a part of glial cells, the glandular epithelium of the stomach, intestines, breast, hepatocytes, heart, skeletal muscle cells, the bronchial and alveolar epithelium, and nephric tubules. In human tissues, the p33ING1 protein, apart from its cytoplasmic distribution, was distributed in the nuclei of the tongue, esophagus, stomach, intestine, lung, trachea, skin, appendix, cervix, endometrium, ovary, and breast. p33ING1 immunoreactivity was strongly detected in the stomach, trachea, skin, cervix, and breast, while it was weak in the other tissues. The positive rate of p33ING1 was 41.0% in the tested cancer entities (489/1,194). In general, p33ING1 expression was restricted to only the cytoplasm for all cancers, whereas it was found in the nucleus of renal clear cells, ovarian and colorectal cancers. Among them, p33ING1 was expressed in more than half of squamous cell carcinomas derived from the esophagus and cervix, while it was rarely expressed in hepatocellular (21.0%) and renal clear cell carcinoma (19.4%).

Conclusions

The findings suggest that p33ING1 might be participated in the repair and regeneration of organs or tissues the repair and regeneration of organs or tissue, and the carcinogenesis of the highly proliferative epithelium.

NKX6.3 controls gastric differentiation and tumorigenesis

NKX6.3 transcription factor is known to be an important regulator in gastric mucosal epithelial differentiation. The present study aimed to investigate whether NKX6.3 acts as an essential tumor suppressor in gastric carcinogenesis. Absent or reduced protein expression and decreased DNA copy number and mRNA transcript of the NKX6.3 gene were frequently observed in gastric cancers. Overexpression of NKX6.3 in AGSNKX6.3 and MKN1NKX6.3 cells markedly arrested cell proliferation by inhibiting cell cycle progression and induced apoptosis through both death receptor- and mitochondrial-pathways. In addition, stable NKX6.3 transfectants increased the expression of gastric differentiation markers, including SOX2 and Muc5ac, and decreased the expression of intestinal differentiation markers, CDX2 and Muc2. In ChIP-cloning and sequencing analyses, NKX6.3 coordinated a repertoire of target genes, some of which are clearly associated with cell cycle, differentiation and death. In particular, NKX6.3 transcriptional factor was found to bind specifically to the upstream sequences of GKN1, a gastric-specific tumor suppressor, and dramatically increase expression of the latter. Furthermore, there was a positive correlation between NKX6.3 and GKN1 expression in non-cancerous gastric mucosae. Thus, these data suggest that NKX6.3 may control the fate of gastric mucosal cells and function as a gastric tumor suppressor.

Identification of 42 Genes Linked to Stage II Colorectal Cancer Metastatic Relapse

Colorectal cancer (CRC) is one of the leading causes of cancer mortality. Metastasis remains the primary cause of CRC death. Predicting the possibility of metastatic relapse in early-stage CRC is of paramount importance to target therapy for patients who really need it and spare those with low-potential of metastasis. Ninety-six stage II CRC cases were stratified using high-resolution array comparative genomic hybridization (aCGH) data based on a predictive survival algorithm and supervised clustering. All genes included within the resultant copy number aberrations were each interrogated independently at mRNA level using CRC expression datasets available from public repositories, which included 1820 colon cancers, and 167 normal colon tissues. Reduced mRNA expression driven by copy number losses and increased expression driven by copy number gains revealed 42 altered transcripts (29 reduced and 13 increased transcripts) associated with metastatic relapse, short disease-free or overall survival, and/or epithelial to mesenchymal transition (EMT). Resultant genes were classified based on gene ontology (GO), which identified four functional enrichment groups involved in growth regulation, genomic integrity, metabolism, and signal transduction pathways. The identified 42 genes may be useful for predicting metastatic relapse in stage II CRC. Further studies are necessary to validate these findings.

Expression of P33(ING1b) Protein in Colorectal Cancer

BACKGROUND

Colorectal cancer (CRC) is the second most common malignancy in the world. However, its mortality rate can be reduced if diagnosed early. P33ING1b is a tumor suppressor protein, which plays a role in growth control and apoptosis. Suppression of p33^ING1b is associated with the loss of cellular growth control. However, p33 ^ING1b expression in CRC and its correlations with clinicopathological factors have been less studied. The aim of this study was to examine p33^ING1b expression in patients with CRC and evaluate its potential correlations with clinicopathological factors.

METHODS

P33^ING1b protein expression was examined in 70 cases of CRC tissue samples and their corresponding neighboring normal tissues by immunhistochemistry. Moreover, p33^ING1b expression in CRC and its correlations with clinicopathological variables including patients’ sex and age, tumor type, location, stage, and differentiation grade were examined.

RESULTS

P33^ING1b expression was significantly lower in tumor samples compared with the normal adjacent samples (p<0.002).

CONCLUSION

Low expression of P33^ING1b in patients with colorectal cancer, may be an important molecular event in the pathogenesis of colorectal cancer. Our data suggest that reduced expression of p33^ING1b may be contribute to tumor genesis and accompanied by the loss of cellular growth control. In fact cell growth is out of control in lower expression of P33 and dysfunctional program cell death. P33 expression might explain the etiology of CRC for reducing the expression of tumor suppressor proteins.

Ectopic expression of p33ING1b suppresses proliferation and induces apoptosis in colonic adenocarcinoma cells

Inhibitor of growth 1b (ING1b) is considered to be a class II tumor suppressor gene. Although decreased expression of p33^ING1b has previously been reported in colorectal cancer (CRC), its role in CRC has remained to be elucidated. The present study was designed to assess the function of p33^ING1b in CRC and to further evaluate its underlying mechanisms of action. Western blot analysis confirmed that ING1b gene expression was significantly decreased in CRC tissues compared with that of adjacent non-tumorous colorectal tissues. Furthermore, recombinant adenovirus-mediated ectopic expression of p33^ING1b resulted in growth inhibition, G1-phase cell cycle arrest and apoptosis in the SW480, HT29 and LoVo colorectal adenocarcinoma cell lines. The results suggested that the downregulation of ING1b contributes to colorectal carcinogenesis and that ectopic expression of ING1b may be a potentially useful therapeutic approach for CRC.

Downregulated inhibitor of growth 3 (ING3) expression during colorectal carcinogenesis

BACKGROUND & OBJECTIVES

ING3 (inhibitor of growth protein 3) overexpression decreased S-phase cell population and colony-forming efficiency, and induced apoptosis at a p53-mediated manner. The aim of this study was to investigate the clinicopathological and prognostic significance of ING3 expression in colorectal carcinogenesis and subsequent progression.

METHODS

ING3 expression was examined by immunohistochemistry on tissue microarray containing colorectal non-neoplastic mucosa (NNM), adenoma and adenocarcinoma. Colorectal carcinoma tissue and cell lines were studied for ING3 expression by Western blot or RT-PCR.

RESULTS

ING3 mRNA was differentially expressed in Colo201, Colo205, DLD-1, HCT-15, HCT-116, HT-29, KM-12, SW480, SW620 and WiDr cells. Carcinomas showed significantly lower ING3 expression than matched NNM at mRNA level (P< 0.05), but not at protein level. Immunohistochemically, ING3 expression was significantly decreased from NNM, adenoma to adenocarcinoma (P< 0.05). ING3 expression was not correlated with age, sex, tumour size, depth of invasion, lymphatic or venous invasion, lymph node metastasis, tumour- node- metastasis staging or differentiation. Kaplan-Meier analysis indicated that ING3 protein expression was not associated the prognosis of the patients with colorectal carcinoma (P< 0.05).

INTERPRETATION & CONCLUSIONS

Our study showed that downregulated ING3 expression might play an important role in colorectal adenoma-adenocarcinoma sequence. Further studies are required to understand the mechanism.

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.

RegulatING chromatin regulators: post-translational modification of the ING family of epigenetic regulators

The five human ING genes encode at least 15 splicing isoforms, most of which affect cell growth, differentiation and apoptosis through their ability to alter gene expression by epigenetic mechanisms. Since their discovery in 1996, ING proteins have been classified as type II tumour suppressors on the basis of reports describing their down-regulation and mislocalization in a variety of cancer types. In addition to their regulation by transcriptional mechanisms, understanding the range of PTMs (post-translational modifications) of INGs is important in understanding how ING functions are fine-tuned in the physiological setting and how they add to the repertoire of activities affected by the INGs. In the present paper we review the different PTMs that have been reported to occur on INGs. We discuss the PTMs that modulate ING function under normal conditions and in response to a variety of stresses. We also describe the ING PTMs that have been identified by several unbiased MS-based PTM enrichment techniques and subsequent proteomic analysis. Among the ING PTMs identified to date, a subset has been characterized for their biological significance and have been shown to affect processes including subcellular localization, interaction with enzymatic complexes and ING protein half-life. The present review aims to highlight the emerging role of PTMs in regulating ING function and to suggest additional pathways and functions where PTMs may effect ING function.

Inhibitor of growth tumor suppressors in cancer progression

The inhibitor of growth (ING) family of tumor suppressors has five members and is implicated in the control of apoptosis, senescence, DNA repair, and cancer progression. However, little is known about ING activity in the regulation of cancer progression. ING members and splice variants seem to behave differently with respect to cancer invasion and metastasis. Interaction with histone trimethylated at lysine 4 (H3K4me3), hypoxia inducible factor-1 (HIF-1), p53, and nuclear factor kappa-B (NF-kappaB) are potential mechanisms by which ING members exert effects on invasion and metastasis. Subcellular mislocalization, rapid protein degradation, and to a lesser extent ING gene mutation are among the mechanisms responsible for inappropriate ING levels in cancer cells. The aim of this review is to summarize the different roles of ING family tumor suppressors in cancer progression and the molecular mechanisms involved.

The ING gene family in the regulation of cell growth and tumorigenesis

The five members of the inhibitor of growth (ING) gene family have garnered significant interest due to their putative roles as tumor suppressors. However, the precise role(s) of these ING proteins in regulating cell growth and tumorigenesis remains uncertain. Biochemical and molecular biological analysis has revealed that all ING members encode a PHD finger motif proposed to bind methylated histones and phosphoinosital, and all ING proteins have been found as components of large chromatin remodeling complexes that also include histone acetyl transferase (HAT) and histone deacetylase (HDAC) enzymes, suggesting a role for ING proteins in regulating gene transcription. Additionally, the results of forced overexpression studies performed in tissue culture have indicated that several of the ING proteins can interact with the p53 tumor suppressor protein and/or the nuclear factor-kappa B (NF-kappaB) protein complex. As these ING-associated proteins play well-established roles in numerous cell processes, including DNA repair, cell growth and survival, inflammation, and tumor suppression, several models have been proposed that ING proteins act as key regulators of cell growth not only through their ability to modify gene transcription but also through their ability to alter p53 and NF-kappaB activity. However, these models have yet to be substantiated by in vivo experimentation. This review summarizes what is currently known about the biological functions of the five ING genes based upon in vitro experiments and recent mouse modeling efforts, and will highlight the potential impact of INGs on the development of cancer.

Expression profiles of mRNA transcript variants encoding the human inhibitor of growth tumor suppressor gene family in normal and neoplastic tissues

The INhibitor of Growth (ING) tumor suppressor gene family is important in regulating cell fate and reads the epigenetic code by interacting specifically with methylated histone H3. Several transcript variants are expressed from the five ING genes but nomenclature for these variants are not consistent in the literature, and very little is known regarding transcript variant expression in normal human tissues and during development. Here we propose a standardized nomenclature for human ING gene family transcript variants and present an expression analysis using real-time quantitative PCR. We establish the steady-state levels of eleven human ING mRNA transcript variants across several fetal, adult, and tumor tissues as well as in cancer-derived cell lines. Consistent with their roles as type II tumor suppressors, we find up to 10,000-fold reduction in many transcript variants in a subset of neoplastic cells. We also find considerable variation in expression levels in different tissues, with up to 1 million-fold higher expression of some ING transcripts in adult, compared to fetal counterparts, particularly in the brain cerebral cortex. These results show differential expression of specific subsets of ING1-5 transcript variants in tissues that may influence the degree to which these variants contribute to epigenetic regulation in cancer and development.

Grow-ING, Age-ING and Die-ING: ING proteins link cancer, senescence and apoptosis

The INhibitor of Growth (ING) family of plant homeodomain (PHD) proteins induce apoptosis and regulate gene expression through stress-inducible binding of phospholipids with subsequent nuclear and nucleolar localization. Relocalization occurs concomitantly with interaction with a subset of nuclear proteins, including PCNA, p53 and several regulators of acetylation such as the p300/CBP and PCAF histone acetyltransferases (HATs), as well as the histone deacetylases HDAC1 and hSir2. These interactions alter the localized state of chromatin compaction, subsequently affecting the expression of subsets of genes, including those associated with the stress response (Hsp70), apoptosis (Bax, MDM2) and cell cycle regulation (p21WAF1, cyclin B) in a cell- and tissue-specific manner. The expression levels and subcellular localization of ING proteins are altered in a significant number of human cancer types, while the expression of ING isoforms changes during cellular aging, suggesting that ING proteins may play a role in linking cellular transformation and replicative senescence. The variety of functions attributed to ING proteins suggest that this tumor suppressor serves to link the disparate processes of cell cycle regulation, cell suicide and cellular aging through epigenetic regulation of gene expression. This review examines recent findings in the ING field with a focus on the functions of protein-protein interactions involving ING family members and the mechanisms by which these interactions facilitate the various roles that ING proteins play in tumorigenesis, apoptosis and senescence.