ING4 induces cell growth inhibition in human lung adenocarcinoma A549 cells by means of Wnt-1/beta-catenin signaling pathway

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.

G9a Promotes Invasion and Metastasis of Non-Small Cell Lung Cancer through Enhancing Focal Adhesion Kinase Activation via NF-κB Signaling Pathway

Potential roles of euchromatic histone methyltransferase 2 (EHMT2 or G9a) in invasion and metastasis are not well understood in non-small cell lung cancer (NSCLC). Here, we investigated the effect and underlying mechanisms of G9a and therapeutic implications of targeting G9a in the invasion and metastasis of NSCLC. Overexpression of G9a significantly enhanced in vitro proliferation and invasion, while knockdown of G9a drastically suppressed in vivo growth and metastasis of A549 and H1299 NSCLC cells. Knockdown or inhibition of G9a significantly decreased the expression of focal adhesion kinase (FAK) protein and activation of FAK pathway. In addition, defactinib, a potent FAK inhibitor, partially abolished the G9a-enhanced invasion in these NSCLC cells. Furthermore, targeting G9a was found to suppress NF-κB transcriptional activity in NSCLC cells through stabilizing NF-κB inhibitor alpha (IκBα), while an NF-κB inhibitor Parthenilide partially abolished the G9a-enhanced FAK activation, which suggests that G9a-enhanced invasion and activation of FAK is mediated by elevated NF-κB activity. Notably, a strong positive correlation between the IHC staining of G9a and phosphorylated FAK proteins was identified in H1299 xenografts and 159 cases of NSCLC tissues (R = 0.408). IMPLICATIONS: The findings of this study strongly demonstrate that G9a may promote invasion and metastasis of NSCLC cells by enhancing FAK signaling pathway via elevating NF-κB transcriptional activity, indicating potential significance and therapeutic implications of these pathways in the invasion and metastasis of NSCLCs that overexpress G9a protein.

Focus-ING on DNA Integrity: Implication of ING Proteins in Cell Cycle Regulation and DNA Repair Modulation

The ING family of tumor suppressor genes is composed of five members (ING1-5) involved in cell cycle regulation, DNA damage response, apoptosis and senescence. All ING proteins belong to various HAT or HDAC complexes and participate in chromatin remodeling that is essential for genomic stability and signaling pathways. The gatekeeper functions of the INGs are well described by their role in the negative regulation of the cell cycle, notably by modulating the stability of p53 or the p300 HAT activity. However, the caretaker functions are described only for ING1, ING2 and ING3. This is due to their involvement in DNA repair such as ING1 that participates not only in NERs after UV-induced damage, but also in DSB repair in which ING2 and ING3 are required for accumulation of ATM, 53BP1 and BRCA1 near the lesion and for the subsequent repair. This review summarizes evidence of the critical roles of ING proteins in cell cycle regulation and DNA repair to maintain genomic stability.

Negative regulators of Wnt signaling in non-small cell lung cancer: Theoretical basis and therapeutic potency

Significant advances in the treatment of non-small cell lung cancer (NSCLC) have been made over the past decade, and they predominantly involve molecular targets such as epidermal growth factor receptor (EGFR) mutations and anaplastic lymphoma kinase (ALK) rearrangements. However, despite the initial good response, drug resistance eventually develops. The Wnt signaling pathway has recently been considered important in embryonic development and tumorigenesis in many cancers, particularly NSCLC. Moreover, the aberrant Wnt pathway plays a significant role in NSCLC and is associated with cancer cell proliferation, metastasis, invasion and drug resistance, and the suppression of canonical or noncanonical Wnt signaling through various biological or pharmacological negative regulators has been proven to produce specific anticancer effects. Thus, blocking the Wnt pathway via its negative regulators may overcome the resistance of current treatment methods and lead to new treatment strategies for NSCLC. Therefore, in this review, we summarize recent studies on the role of negative regulators in Wnt signaling in NSCLC and the therapeutic potency of these molecules as agents and targets for NSCLC treatments.

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.

MicroRNA-650 targets inhibitor of growth 4 to promote colorectal cancer progression via mitogen activated protein kinase signaling

Colorectal cancer (CRC) is the third most common malignant disease globally and causes numerous cancer-associated mortalities; however, the underlying molecular mechanisms remain unresolved. MicroRNAs (miRs) are endogenous noncoding RNAs that regulate post-transcriptional gene silencing by annealing to partially complementary sequences in the 3′-untranslated regions of target mRNAs. In the present study, expression of the tumor suppressor gene inhibitor of growth protein 4 (ING4) in cell lines was investigated using reverse transcription-quantitative polymerase chain reaction and western blotting. miR-650 overexpression promoted CRC cell proliferation and migration by targeting ING4 when the cells were transfected with the miR-650 mimics. Additionally, overexpression of miR-650 increased the epithelial-mesenchymal transition and activation of the Ras homolog gene family member A/Ras-related C3 botulinum toxin GTPase. Extracellular signal-regulated kinases and p38 mitogen-activated protein kinase signaling were markedly activated when miR-650 was increased in CRC cells. Combined, the results indicate the mechanism underlying the miR-650 promotion of CRC progression, and provide promising potential biomarkers for the prognosis and treatment of CRC.

Enhanced anti-melanoma efficacy of interferon α-2b via overexpression of ING4 by enhanced Fas/FasL-mediated apoptosis

Melanoma, is a highly aggressive and the most lethal form of skin cancer, and is known to be resistant to current therapeutic modalities. Interferon (IFN)-α2b is an immunostimulatory cytokine and is used to treat melanoma by inhibiting proliferation and promoting apoptosis of cells. However, there is a need to improve the efficacy of IFN-α2b. Inhibitor of growth family member 4 (ING4) has been reported to function as a tumor suppressor and is involved in regulating cell cycle progression, apoptosis, cell migration and invasion. Previously studies have also reported that caspase-3, caspase-8, poly (ADP-ribose) polymerase (PARP) and Fas/Fas ligand (FasL) pathways are involved in the process of apoptosis. In the present study, it was investigated whether overexpression of ING4 is able to enhance IFN-α2b response in human melanoma cells. It was determined that the overexpression of ING4 was able to increase the effects of IFN-α2b, and induce cell death and apoptosis in melanoma cells. Furthermore, the overexpression of ING4 resulted in decreased expression of PARP, caspase-3 and -8. The expression of cleaved PARP, cleaved caspase-3, cleaved caspase-8, Fas and FasL was increased in the A375 melanoma cell line. These results demonstrate that the overexpression of ING4 is able to enhance the anti-melanoma activity of IFN-α2b. These findings provide a potential therapeutic strategy where a combination of ING4 overexpression and IFN-α2b treatment may lead to higher levels of apoptosis in melanoma cells.

Role of inhibitor of growth 4 in the suppression of human melanoma cells through the Fas/FasL-mediated apoptosis pathway

Melanoma, the most aggressive form of skin cancer, is notoriously resistant to all current available therapies. Inhibitor of growth 4 (ING4), a novel member of the ING family of proteins, has previously been shown to play a critical role in the development of multiple tumors by regulating apoptosis, proliferation, cell cycle progress, migration and invasion. However, the functional role of ING4 in human melanoma remains unclear. To fully understand its potential role in human melanoma, in the present study, lentivirus (LV)‑ING4 and LV‑ING4‑short hairpin RNA were constructed and transfected into human melanoma A375 cells. First, the effect of overexpressing or downregulating ING4 on the apoptosis of the transfected melanoma cells and cluster of differentiation (CD)3+ T cells was investigated. In the present study, we found that the late apoptotic cells, and not the early apoptotic cells, were more in LV-ING4 group compared with LV-control, and both the early and late apoptosis of CD3+ T cells was significantly observed in A375 cells transfected with LV-ING4 compared with LV-control. Importantly, it was determined whether the overexpression of ING4 significantly induce apoptotic cell death via Fas/FasL (Fas death receptor/FasL) pathway activation and downregulation of poly(ADP‑ribose) polymerase, caspase‑3 and caspase‑8 in the melanoma cells and CD3+ T cells. These results demonstrated that overexpression of ING4 can induce the apoptosis of melanoma cells and CD3+ T cells through signaling pathways such as the Fas/FasL pathway, and that ING4 gene therapy for melanoma treatment is a novel approach.

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.

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.

Wnt signaling as potential therapeutic target in lung cancer

INTRODUCTION

Wingless-type (Wnt) signaling is tightly regulated at multiple cellular levels and is dysregulated in lung cancer. Therefore, it offers therapeutic targets for developing novel agents for lung cancer treatment.

AREAS COVERED

In this article, we discuss the role of the Wnt signaling pathway in lung cancer, highlighting the aberrant activation of Wnt in lung cancer stem cells and its implication in resistance to radiotherapy, chemotherapy and targeted therapy. We also expound the regulatory roles of microRNAs in Wnt signaling, as well as the potential of the Wnt pathway to provide biomarkers and therapeutic targets in lung cancer. The potential use of small molecule and biological inhibitors targeting the Wnt pathway for lung cancer therapy and prevention is also discussed.

EXPERT OPINION

Wnt signaling plays an important role in the development and metastasis of lung cancer; the pathway provides targets to develop agents towards for cancer prevention and therapy. A number of clinical trials have shown the effectiveness of Wnt pathway inhibitors in epithelial tumors. However, the side effects should be considered. Nevertheless, the results from clinical studies suggest that inhibitors targeting the Wnt signaling show promise against lung cancer.

TGIF1 promoted the growth and migration of cancer cells in nonsmall cell lung cancer

Transforming growth factor beta-inducing factor 1 (TGIF1) was reported to be dysregulated in several types of cancer. However, its expression pattern and functions in nonsmall cell lung cancer (NSCLC) remained unknown. In the present study, the expression of TGIF1 was found to be elevated in the clinical NSCLC tissues. TGIF1 promoted the growth and migration of NSCLC cells, while knocking down the expression of TGIF1 inhibited the growth and migration of NSCLC cells. Moreover, downregulation of TGIF1 impaired the metastasis of NSCLC cells. In the study for the molecular mechanisms, it was found that TGIF1 positively regulated beta-catenin/TCF signaling. In summary, our study demonstrated the oncogenic role of TGIF1 in NSCLC, and TGIF1 might be a therapeutic target for NSCLC.

Low ING4 protein expression detected by paraffin-section immunohistochemistry is associated with poor prognosis in untreated patients with gastrointestinal stromal tumors

BACKGROUND

Inhibitor of growth 4 (ING4) has deserved attention as a tumor suppressor gene in many malignant tumors. In our study, we investigated ING4 immunoexpression in gastrointestinal stromal tumors (GISTs) and its prognostic value.

METHOD

The expression of ING4 and Ki67 was investigated in 41 samples of various risk gastrointestinal stromal tumors by immunohistochemical technique. The associations of ING4 expression and clinicopathological parameters, and prognosis of the patients, were analyzed by multivariate Cox regression analysis.

RESULTS

ING4 expression showed a decreased trend from lower-risk to high-risk gastrointestinal stromal tumors, and an opposite trend for Ki67 expression. In lower-risk tumors, it was found the expression level of ING4 was 78.95 % ± 27.90 % and that of Ki67 was 4.42 % ± 3.75 %. However, in high-risk tumors, the expression level of ING4 was 9.23 % ± 7.66 % and that of Ki67 was 18.50 % ± 9.09 %. There was a strongly negative correlation between the expression levels of ING4 and Ki67. A significant difference was observed in the expression of ING4 between invasion and non-invasion (p < 0.001). The expression of ING4 was markedly correlated with tumor size (p < 0.001), mitotic index (p < 0.001), tumor necrosis (p = 0.021), invasion (p < 0.001), recurrence and metastasis (p = 0.021), and mortality (p < 0.001).

CONCLUSION

The low expression level of ING4 protein was correlated with high-risk GISTs. ING4 might be involved in the progression of GISTs and inhibit its invasion. ING4 might be one of the prognostic indicators in GISTs.

Tumor suppressor ING4 overexpression contributes to proliferation and invasion inhibition in gastric carcinoma by suppressing the NF-κB signaling pathway

There is growing evidence that inhibitor of growth 4 (ING4) plays a pivotal role in development and progression of multiple different tumors; however, its precise function in gastric carcinoma remains to be elucidated. In the present study, we investigated ING4 level in gastric carcinoma tissues and cells, and preliminarily elucidated the role of ING4 in the proliferation and invasion of gastric carcinoma. The results demonstrated that expressions of ING4 mRNA and protein in gastric carcinoma tissues and cells were significantly lower than those in normal tissues and cells (P < 0.05). ING4 level in gastric carcinoma cells stably expressing ING4 was markedly higher than those in untreated group and empty vector pcDNA3.1 group (P < 0.05). Elevated ING4 level resulted in the inhibition of proliferation and invasion in three of gastric carcinoma cell lines MKN-28, SGC-7901 and MKN-45. Most notably, increased ING4 level evidently evoked the down-regulation of p65, p-IκBα, MMP-9 and uPA proteins and the up-regulation of IκBα protein. Our results presented herein suggest that ING4 level elevation mediated proliferation and invasion inhibition may be tightly associated with the suppression of NF-κB signaling pathway.

ING4 is negatively correlated with microvessel density in colon cancer

ING4 is a novel tumor suppressor which is downregulated in a number of cancers. In this study, we investigated the role of ING4 in tumor angiogenesis in colorectal carcinoma (CRC) patients. Semi-quantitative RT-PCR, western blots, and immunohistochemistry were used to determine ING4 mRNA and protein expression in CRC and normal tissue from 60 CRC specimens and 30 colonic adenoma specimens. The correlation between ING4 expression and clinical stage, histological grade as well as lymph node metastasis was evaluated. Immunohistochemistry was performed to explore the correlation between ING4 expression and microvessel density (MVD) in CRC. CRC tissue had significantly lower levels of ING4 mRNA and protein compared to colonic adenoma and normal intestinal tissue. Immunostaining showed ING4 expression in 38 (63.3 %), 30 (100 %), and 60 (100 %) cases of normal colonic mucosa, adenoma, and normal intestinal mucosal tissue, respectively. Lower ING4 levels correlated with higher clinical stage and histological grade. ING4 mRNA and protein levels were significantly lower in CRC patients with lymph node metastasis compared to patients without lymph node metastasis (0.41 ± 0.30 vs. 0.91 ± 0.29 and 0.60 ± 0.21 vs. 0.87 ± 0.27, respectively; p < 0.001). Importantly, ING4 mRNA and protein levels were negatively correlated with MVD in CRC patients (p < 0.001). Our data suggest that ING4 levels are a potential biomarker of CRC progression and that ING4 may inhibit tumor growth by modulating angiogenesis in CRC.

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.

Identification of ING4 (inhibitor of growth 4) as a modulator of docetaxel sensitivity in human lung adenocarcinoma

Resistance to docetaxel (DTX) usually occurs in patients with lung adenocarcinoma. To better elucidate the underlying molecular mechanisms involved in resistance to DTX-based chemotherapy, we established a DTX-resistant lung adenocarcinoma cell line (SPC-A1/DTX). By gene array analysis, the expression of ING4 was found to be significantly downregulated in SPC-A1/DTX cells. Additionally, the decreased expression of the ING4 gene was induced upon DTX treatment of SPC-A1 cells. Overexpression of ING4 reverses DTX or paclitaxel resistance of DTX-resistant lung adenocarcinoma cells (SPC-A1/DTX or A549/Taxol) by inducing apoptosis enhancement and G₂/M arrest, and small interfering RNA-mediated ING4 knockdown renders DTX-sensitive lung adenocarcinoma cells more resistant to DTX or paclitaxel. Also, overexpression of ING4 could enhance the in vivo sensitivity of SPC-A1/DTX cells to DTX. The phenotypical changes of SPC-A1/DTX cells induced by overexpression of ING4 might be associated with the decreased ratio of Bcl-2/Bax, which resulted in the activation of caspase-3. The level of ING4 expression in tumors of nonresponding patients was significantly lower than that in those of responders, suggesting that the expression of ING4 was positively correlated with tumor response to DTX. Our results provide the first evidence that ING4 might be essential for DTX resistance in lung adenocarcinoma. Thus, ING4 will be a potential molecular target for overcoming resistance to DTX-based chemotherapies in lung adenocarcinoma.

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.

Effects of respiratory mechanical forces on the pharmacological response of lung cancer cells to chemotherapeutic agents

In vitro screening of chemotherapeutic agents is routinely carried out in static monolayer cell cultures. However, drugs administered to patients act in the presence of various microenvironments in vivo. For example, in lung tumors, mechanical forces are constantly present and do affect the physiological response of the lung tissue to a variety of therapeutic agents. We hypothesized that mechanical forces may affect the response of lung tumors to chemotherapeutic agents and studied the effects under simulated conditions. First, we examined the effects of simulated forces that approximate normal respiration on the proliferation and morphology of NCI-H358 and A549 cell lines. Then, we studied the effects of the simulated forces on the ability of Paclitaxel, Doxorubicin, Cisplatin, Zactima and an experimental drug to induce cytotoxicity in both cell lines. Cells were treated with the drugs in the presence or absence of simulated forces (20% maximum strain and 15 cycles/minute) that approximate human lung expansion and contraction. Cell proliferation and the effectiveness of the drugs were assessed. Using a standard exponential cell growth model, it was determined that mechanical forces significantly reduced the proliferation of both cell lines. Interestingly, forces also significantly lowered the effectiveness of all drugs except Zactima in A549 cells, while in NCI-H358 cells, Zactima was the only drug that demonstrated an increase in effectiveness owing to applied forces. Our results demonstrate that mechanical forces have significant impact on cell survival and chemotherapeutic efficacy and may be of significance in engineering improved screening assays for antitumor drug discovery.

Downregulated expression of inhibitor of growth 4 (ING4) in advanced colorectal cancers: a non-randomized experimental study

Colorectal cancer has a high cure rate if it can be detected early. Identifying and understanding the genes involved may enable early diagnosis and reduce mortality. The aim of our study was to investigate the correlation between the expression of ING4 and the pathological features in patients with colorectal cancer. We assayed ING4 protein expression levels in tumor samples from 97 patients diagnosed with colorectal cancer between January 2001 and January 2002. The patients received no other treatments except surgery. ING4 protein expression was downregulated in adenoma relative to normal mucosa and further reduced in colorectal cancer tissues. Furthermore, the suppression of ING4 expression was also related to the more advanced Dukes' stages. We observed that ING4 expression levels in patients with lymphatic metastasis were lower than those without metastasis. Together, our results indicate that ING4 play a role in colorectal carcinoma progression.

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.

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.

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

ING4 is a candidate tumor suppressor gene that is deleted in 10% to 20% of human breast cancers and is mutated in various human cancer cell lines. To evaluate whether ING4 has a tumor-suppressive role in breast tissue, we overexpressed it in mouse mammary glands using a transplant system. Ectopic expression of ING4 suppressed MYC-induced mammary hyperplasia, but not tumorigenesis. In the same model system, we show that a COOH-terminal truncation mutant of ING4 found in human cancer cells could act alone to induce abnormal gland structures resembling mammary hyperplasia, which did not progress to tumors. However, coexpression of the ING4 mutant with MYC increased the penetrance and metastasis of MYC-initiated mammary tumors, giving rise to tumors with more organized acinar structures. Similarly, in vitro expression of the ING4 mutant in MCF10A mammary epithelial cells reinforced tight junctional structures. Our results provide direct functional evidence that ING4 could suppress the early stages of breast cancer and that dominant mutant alleles of ING4 might contribute to malignant development.

Inhibitor of growth 4 induces apoptosis in human lung adenocarcinoma cell line A549 via Bcl-2 family proteins and mitochondria apoptosis pathway

OBJECTIVE

Inhibitor of growth 4 (ING4) is considered to be a tumor suppressor implicated in several human malignancies by tumor growth inhibition and apoptosis enhancement. In present study, the effects of ING4 on apoptosis and its mechanisms were investigated through the transduction of ING4 cDNA into lung adenocarcinoma cell line A549.

METHODS

The effects of ING4 on A549 apoptosis were observed by FCM analysis, TUNEL assay, and electron microscopy. Simultaneously, the effects of ING4 on the expression of several apoptosis-related proteins in cell line A549 were evaluated by Western blot analysis.

RESULTS

Both Annexin-V FITC analysis by FCM and TUNEL assay revealed more apoptotic cells in A549 cells with exogenous ING4 gene. For electron microscopy, A549 cells with exogenous ING4 gene showed typical morphological changes of apoptosis. The deregulation of Bcl-2 family proteins (Bcl-2, Bcl-xl, Bax, Bak, Bid) and the major apoptotic executioners of mitochondria pathway (Cyt-c, caspase3, PARP) were also observed.

CONCLUSION

Our findings suggest that exogenous ING4 can enhance A549 apoptosis via regulating the expression of Bcl-2 family proteins and the activation of mitochondrial apoptotic pathway.