Mutational analysis of the candidate tumor suppressor gene ING1 in Indian oral squamous cell carcinoma

The ING family tumor suppressors: from structure to function

The Inhibitor of Growth (ING) proteins belong to a well-conserved family which presents in diverse organisms with several structural and functional domains for each protein. The ING family members are found in association with many cellular processes. Thus, the ING family proteins are involved in regulation of gene transcription, DNA repair, tumorigenesis, apoptosis, cellular senescence and cell cycle arrest. The ING proteins have multiple domains that are potentially capable of binding to many partners. It is conceivable, therefore, that such proteins could function similarly within protein complexes. In this case, within this family, each function could be attributed to a specific domain. However, the role of ING domains is not definitively clear. In this review, we summarize recent advances in structure-function relationships in ING proteins. For each domain, we describe the known biological functions and the approaches utilized to identify the functions associated with ING proteins.

Molecular pathology of the FSH receptor: new insights into FSH physiology

Manipulations of mouse genome have helped to elucidate gonadotrophin function but important differences subsist between rodent and human reproduction. Studies of patients with mutations of gonadotrophins or gonadotrophin receptors genes allow understanding their physiological effects in humans. The correlation of the clinical phenotypes of patients with in vitro studies of the mutated receptor residual function and histological and immunohistological studies of the ovarian biopsies permits to understand which stages of follicular development are under FSH control. Total FSH receptor (FSHR) inactivation causes infertility with an early block of follicular maturation remarkably associated with abundant small follicles as in prepubertal ovaries and demonstrates the absolute requirement of FSH for follicular development starting from the primary stage. Partial FSHR inactivation, characterized by normal-sized ovaries, can sustain follicular development up to the early antral stages but incremental levels of FSH stimulation seem to be required for antral follicular growth before selection. These findings contrast with the traditional view of an initial gonadotrophin-independent follicular growth prior to the preantral-early antral stages. The presence of numerous reserve follicles in the ovaries of these patients may permit a future treatment of their infertility. The study of reduced FSHbeta or FSHR activity in genetically modified male mice models and in men suggests a minor impact of the FSHR on masculine fertility. Further studies on patients with a demonstrated total FSHbeta or FSHR inactivation are required to elucidate reported differences in spermatogenesis impairment. Finally, the studies of mutations of gonadotrophins and their receptors demonstrate differences in gonadotrophin function between genetically modified rodents and humans which suggest prudence in extrapolating observations in rodents to human reproduction. Ovarian hyperstimulation syndrome (OHSS) can infrequently arise spontaneously during pregnancy, but most often it is an iatrogenic complication of ovarian stimulation treatments with ovulation drugs for in vitro fertilization. The first genetic cause of familial recurrent spontaneous OHSS was identified as a broadening specificity of the FSHR for hCG due to naturally occurring heterozygous mutations located unexpectedly in the transmembrane domain of the FSHR. Broadening specificity of a G protein-coupled receptor is extremely rare. These observations led to the identification of the etiology of this previously unexplained syndrome and permitted to conceive novel models of FSHR activation. Susceptibility to iatrogenic OHSS or its clinical severity may be associated with FSHR polymorphisms with slightly different activities in vivo as suggested by several studies. The study of larger cohorts is needed to evaluate the clinical impact of these observations in the management of patients undergoing IVF protocols.

Nuclear to cytoplasmic shift of p33(ING1b) protein from normal oral mucosa to oral squamous cell carcinoma in relation to clinicopathological variables

PURPOSE

p33(ING1b), as a candidate tumour suppressor gene, has been found to be expressed a proportion of oral squamous cell carcinomas (OSCCs), however, its clinicopathological significance is not studied yet. Our aim was to investigate association of p33(ING1b) expression with clinicopathological variables and particularly interesting new cysteine-histidine rich protein (PINCH) in OSCCs.

METHODS

p33(ING1b) expression was immunohistochemically examined in 20 normal oral mucosa specimens and 49 OSCCs.

RESULTS

Normal squamous cells showed only p33(ING1b )nuclear expression (no cytoplasmic expression), with a rate of 90% positive cases. While 24% of OSCCs appeared cytoplasmic expression (11 of them with weak nuclear staining) and the rest tumours (76%) were negative for p33(ING1b). Furthermore, the cases having lymph node metastasis showed a higher frequency of positive cytoplasmic expression than those without metastasis (P = 0.03). The p33(ING1b) cytoplasmic expression was positively related to PINCH expression (P = 0.04), the cases positive for both proteins had a high rate of the metastasis (P = 0.03).

CONCLUSIONS

The transfer of p33(ING1b) protein from the nucleus to the cytoplasm may result in loss of normal cellular function of the protein, which might play a role in the tumourigenesis and metastasis of OSCCs.

Clinical, pathological, cellular and molecular lesions caused by oral smokeless tobacco - a review

While carcinogenicity of smokeless tobacco (ST) to humans is well established the oral lesions that precede development of cancer are less well characterized. The clinical appearances of ST-associated lesions are variable. Epidemiological studies show a strong significant association of risk with chronic daily use but population differences are noted because of various commercial products in use. Morphological features observed are some what different to oral lesions caused by smoking and oral dysplasia in ST-associated lesions is less common. Effects of ST on oral keratinocytes observed in vitro include alterations in cell proliferation, apoptosis and activation of inflammatory markers. Genetic aberrations caused by ST include activation of ras, uncommon in smokers but mutational hot spots in p53 encountered are similar to those in smokers.

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.

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

AIM: To explore the effect and significance of inhibitor of growth 1 (ING1) gene in carcinogenesis and progression of human sporadic colorectal cancer.

METHODS: mRNA expression, mutation, and loss of heterozygosity (LOH) of ING1 gene in 35 specimens of sporadic colorectal cancer tissues and the matched normal mucous membrane tissues were detected by semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR), PCR-single strain conformation polymorphism (PCR-SSCP) and PCR-simple sequence length polymorphism (PCR-SSLP) using microsatellite markers, respectively.

RESULTS: The average ratios of light intensities of p33^ING1b and p47^ING1a mRNA expression in the cancerous tissues were significantly lower than those in normal tissues. The difference between the two mRNA splices was not significant in the matched tissues. In addition, the ratios of light intensities of p33^ING1b and p47^ING1a mRNA expression in the cancerous tissues of Dukes?stages C and D were significantly lower than those in cancerous tissues of Dukes?stages A and B. However, no mutation of ING1 gene was detected in all 35 cases; only 4 cases of LOH (11.4%) were found.

CONCLUSION: p33^ING1b and p47^ING1a mRNA expressions are closely related with the carcinogenesis and progression of human sporadic colorectal cancer. No mutation of ING1 gene is found, and there are only few LOH in sporadic colorectal cancers. These might not be the main reasons for the down regulation of ING1 expression. Its low expression may happen in transcription or post-transcription.

Function of the ING family of PHD proteins in cancer

The ING genes encode a family of at least seven proteins with conserved plant homeodomain (PHD)-type zinc fingers in their C-termini. The founding member, ING1, is capable of binding to and affecting the activity of histone acetyltransferase (HAT), histone deacetylase (HDAC), and factor acetyltransferase (FAT) protein complexes. Some ING proteins are involved in transcriptional regulation of genes, such as the p53-inducible genes p21 and Bax. Others have been found to affect post-translational modifications, exemplified by the ING2-induced acetylation of p53 on the same site deacetylated by the Sir2 HDAC. Upon UV irradiation, ING1 causes cell cycle arrest and interacts with proliferating cell nuclear antigen to promote DNA repair or induce apoptosis in cells to prevent tumorigenesis depending upon the severity of DNA damage. It is very likely that, by linking DNA repair, apoptosis and chromatin remodeling to the transcriptional regulation of critical genes, ING1 exerts it tumor suppressor functions by helping maintain genomic stability. Therefore, ING proteins, which are down-regulated in a broad variety of cancer types, are able to restrict cell growth and proliferation, induce apoptosis, and modulate cell cycle progression, which strongly supports the notion that ING family proteins act as class II tumor suppressors.

Epigenetic and genetic alterations of p33 ING1b in ovarian cancer

p33ING1b is a candidate tumor suppressor gene and a nuclear protein. We investigated whether genetic and epigenetic mechanisms affect p33ING1b expression in ovarian cancer thus contributing toward its pathogenesis. A total of 111 ovarian cancers collected from Beijing and Hong Kong were used for this study. Weak or negative p33ING1b protein expression was demonstrated by immunohistochemistry on tissue microarray in 28/111 cases. Real-time quantitative RT-PCR also showed overall significant reduction of p33ING1b mRNA expression (P = 0.0137), with 53.1% (17/32) cases showing 2- to 5-fold reduction and absence of expression. The reduction of mRNA expression in cancer correlated with decreased p33ING1b protein expression (P < 0.0001). While no p33ING1b mutation was found, allelic loss at the p33ING1b locus was demonstrated in 25% (8/32) cases. The allelic loss profiles also showed statistical significant correlation with reduction of p33ING1b protein and mRNA expression (P = 0.031 and 0.030). Promoter methylation as assessed by methylation specific PCR was found in 23.9% (21/88) cases analyzed. Bisulfite sequencing results confirmed the p33ING1b promoter methylation status of these methylation positive cases. Statistical significant correlation between methylation and mRNA expression (P = 0.006) was demonstrated. Treatment with demethylating drug, 5'-aza-2'-deoxycytidine, resulted in dosage-dependent elevated mRNA expression of p33ING1b in ovarian cancer cell lines. This is the first study reporting epigenetic mechanism regulating the p33ING1b expression. Our findings support that genetic and epigenetic alteration of p33ING1b are likely to contribute towards the pathogenesis of ovarian cancers.

Growth inhibition by the tumor suppressor p33ING1 in immortalized and primary cells: involvement of two silencing domains and effect of Ras

ING1 was identified as an inhibitor of growth and has been described as a tumor suppressor. Furthermore, the expression of ING1 is induced in senescent cells and antisense ING1 extends the proliferative life span of primary human fibroblasts. Cooperation of p33ING1 with p53 has been suggested to be an important function of ING1 in cell cycle control. Intriguingly, it has been shown that p33ING1 is associated with histone acetylation as well as with histone deacetylation function. Here we show that p33ING1 is a potent transcriptional silencer in various cell types. However, the silencing function is independent of the presence of p53. By use of deletion mutants two potent autonomous and transferable silencing domains were identified, but no evidence of an activation domain was found. The amino (N)-terminal silencing domain is sensitive to the histone deacetylase inhibitor trichostatin A (TSA) whereas the carboxy-terminal silencing function is resistant to TSA, suggesting that p33ING1 confers gene silencing through both HDAC-dependent and -independent mechanisms. Interestingly, the presence of oncogenic Ras, which is able to induce premature senescence, increases the p33ING1-mediated silencing function. Moreover, ING1-mediated silencing was reduced by coexpressing dominant-negative Ras or by treatment with the mitogen-activated protein kinase inhibitor PD98059 but not by treatment with SB203580, an inhibitor of the p38 pathway. In addition, we show that both silencing domains of ING1 are involved in cell cycle control, as measured by inhibition of colony formation of immortalized cells and by thymidine incorporation of primary human diploid fibroblasts (HDF). Interestingly, p33ING1 expression induces features of cellular senescence in HDFs.

Genetic alterations and reduced expression of tumor suppressor p33ING1b in human exocrine pancreatic carcinoma

AIM: To detect the expression of p33^ING1b protein and the change of p33^ING1b gene in pancreatic carcinoma and to evaluate the significance of p33^ING1b in pancreatic cell carcinogenesis.

METHODS: Pathological specimens from pancreatic carcinoma and matched non-tumor pancreatic tissues were examined for p33^ING1b expression and mutation by immunohistochemistry, polymerase chain reaction single-strand conformation polymorphisms (PCR-SSCP) and loss of heterozygosity (LOH).

RESULTS: The rate of p33^ING1b protein expression was 85% (34/40). A single germline missense mutation was detected in 1 of 40 tumors located at codon 215: TGC-TCC (Cys-Ser). Fourteen (60.9%) of 23 tumor samples showed LOH in all of the informative markers tested, but no mutation was detected in these tumors and only two of the informative tumors lacked expressions of p33^ING1b protein.

CONCLUSION: Mutation and loss of expression are not the main reasons for the disfunction of p33^ING1b in pancreatic carcinoma, an abnormality at the level of chromosome and/or transcription may inhibit their normal functions, potentially contributing to pancreatic cell carcinogenesis.

Phylogenetic analysis of the ING family of PHD finger proteins

Since the discovery of ING1 class II tumor suppressors in 1996, five different ING genes (ING1 to ING5) encoding proteins with highly conserved plant homeodomain (PHD) motifs and several splicing isoforms of the ING1 and ING2 gene have been identified. The ING family functions in DNA repair and apoptosis in response to UV damage through binding to proliferating cell nuclear antigen (PCNA); chromatin remodeling and regulation of gene expression through regulating and/or targeting histone acetyltransferase/deacetylase (HAT/HDAC) activities; binding targets of rare phosphatidylinositol phosphates (PtdInsPs) that function in DNA damage-initiated stress signaling; and regulating brain tumor angiogenesis through transcriptional repression of NF-KB-responsive genes. To elucidate the evolutionary history of ING proteins and summarize what is known about regions highly conserved in the ING family members, we have examined the sequences and phylogenetic relationships of ING proteins across taxonomically diverse organisms. We have identified novel ING family members in rats, frogs, fish, mosquitoes, fruit flies, worms, fungi, and plants. We have also clarified the naming and classification of ING proteins based on our phylogenetic analysis to allow better understanding of the ING protein family. Using sequence similarities, we have identified novel regions and motifs of unknown function that are conserved across family members. An evolutionary history for the ING family of PHD finger proteins is presented that indicates that five ING genes are present in vertebrates. Three of these may be paralogs of ING genes found in arthropods, whereas nematodes, fungi, and green plants contain ING genes that have general features of the vertebrate ING family.

The role of the tumour suppressor p33 ING1b in human neoplasia

The inhibitor of growth (ING) genes (ING1-4) probably descend from tumour suppressor genes. ING1 was the first to be identified and later isolated using an approach to detect genes whose expression is suppressed in cancer. The others were isolated through homology and similarity searches in human and mouse databases. All members contain a plant homeodomain involved in macromolecule recognition. Apart from the extensively studied ING1, little is known about the number of transcripts encoded by the other members or their gene structure. ING1 encodes several differentially spliced mRNAs, which may produce a family of proteins. The most widely expressed protein isoform is p33(INGb1), which is involved in restriction of cell growth and proliferation, apoptosis, tumour anchorage independent growth, cellular senescence, maintenance of genomic stability, and modulation of cell cycle checkpoints. ING1 gene mutation is uncommon in cancer, although the subcellular localisation of p33(INGb1) may have an effect on its function. The p33(INGb1) cellular compartmental shift from the nucleus to the cytoplasm may cause loss of normal cellular function, and may play a central role in the pathogenesis of several cancers.

Different HATS of the ING1 gene family

The ING family of proteins are involved in chromatin remodelling, and bind to and affect the activity of histone acetyltransferase, histone deacetylase, and factor acetyltransferase protein complexes. Some family members affect transcription, including the expression of p53-inducible genes such as p21 and Bax, and ING2 induces p53 acetylation on a site implicated in the regulation of p53 activity. ING1 promotes DNA repair and interacts with proliferating cell nuclear antigen, thus linking DNA repair, apoptosis and chromatin remodelling. Here, we summarize what is known about the molecular interactions of ING1 family proteins and, based on these interactions, develop a model to better understand the impact of ING proteins on multiple biological processes.

Loss of nuclear expression of the p33(ING1b) inhibitor of growth protein in childhood acute lymphoblastic leukaemia

BACKGROUND/AIMS

p33(ING1b) is a tumour suppressor protein involved in growth control and apoptosis. Suppression of p33(ING1b) expression is associated with the loss of cellular growth control and immortalisation, whereas its overexpression causes cell cycle arrest. Moreover, normal p33(ING1b) expression is essential for optimal function of p53. Acute lymphoblastic leukaemia (ALL) is the most common malignancy of childhood, accounting for one third of all childhood malignancies. A variety of cytogenetic abnormalities have been described but there is no single abnormality common to all cases. Deregulation of the TP53 pathway is a common genetic abnormality in human malignancies. However, TP53 mutations are uncommon in ALL. It is possible that alternative mechanisms of regulation of the TP53 apoptosis pathway, such as modulation of p33(ING1b) expression, may be important in ALL. The aim of this study was to assess the expression of p33(ING1b) in childhood ALL.

METHODS

One hundred and forty five patients with childhood ALL were investigated in this immunohistochemical study of the expression of p33(ING1b).

RESULTS

Loss of nuclear expression of p33(ING1b) was seen in 78% of cases. This was associated with increased cytoplasmic expression of the protein. Kaplan Meier survival analysis demonstrated a trend towards a better prognosis for patients with tumours that had lost nuclear p33(ING1b).

CONCLUSION

These results suggest that the loss of nuclear p33(ING1b) expression may be an important molecular event in the pathogenesis of childhood ALL.

Relative levels of alternative transcripts of the ING1 gene and lack of mutations of p33/ING1 in haematological malignancies

The protein product of the ING1 gene physically interacts with p53 and appears necessary for the role of p53 in growth inhibition/apoptosis. Alternative splicing of the ING1 gene produces three transcripts: p24/ING1-ALT1, p47/ING1-ALT2 and p33/ING1. A competitive RT-PCR, which determines the relative levels of these transcripts, was employed to study peripheral blood lymphocytes from 49 patients with haematological malignancies and five normal controls. Both groups expressed predominantly the p33/ING1 transcript, with low levels of p24/ING1 and p47/ING1. We screened the complete p33/ING1 transcript for sequence variations, by non-isotopic RNase cleavage assay (NIRCA); none were found. This study suggests that neither perturbation of alternative splicing, nor mutation of p33/ING1 plays a significant role in the development of haematological malignancies.

Comparative assessment expression of the inhibitor of growth 1 gene (ING1) in normal and neoplastic tissues

Studies have indicated that the tumor suppressor p33(ING1b) (13q33-34) interact with p53. Moreover, the association of functional protein forms of each member of the p33(ING1b)/p53 complex is essential for optimum activity of p53. The present report describes the sequencing of cDNAs corresponding to the p33(ING1b) mRNAs in a series of normal and tumor cell lines, and the production of monoclonal antibodies (MAbs) reactive with p33(ING1b). These antibodies were subsequently used to analyze p33(ING1b) expression in normal and tumor cell lines and tissues. No evidence of mutation of p33(ING1b) was found in any of the 15 tumor cell lines cDNAs studied. Our investigation of a wide range of normal tissues have shown that expression of the nuclear epitope is highly ubiquitous, whereas expression of the cytoplasmic form could be detected in only 50% of tissues studied. Considering neoplastic tissues, loss of nuclear p33(ING1b) was observed in melanoma, seminoma, papillary thyroid carcinoma, ductal breast carcinoma, and acute lymphoblastic leukemia. As with normal tissue, cytoplasmic p33(ING1b) was more restricted, being observed in around 30% of neoplastic tissues, but in melanoma, papillary thyroid carcinoma, ductal breast carcinoma, there was increased detection of cytoplasmic p33(ING1b) associated with concomitant loss of nuclear expression. These results may suggest that at least in some tumors, loss of effective p33(ING1b) function may be achieved by translocation to the cytoplasm or failure of nuclear localization.