Expression of novel ING variants is regulated by thyroid hormone in the Xenopus laevis tadpole

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.

ING1 and ING2: multifaceted tumor suppressor genes

Inhibitor of Growth 1 (ING1) was identified and characterized as a "candidate" tumor suppressor gene in 1996. Subsequently, four more genes, also characterized as "candidate" tumor suppressor genes, were identified by homology search: ING2, ING3, ING4, and ING5. The ING proteins are characterized by a high homology in their C-terminal domain, which contains a Nuclear Localization Sequence and a Plant HomeoDomain (PHD), which has a high affinity to Histone 3 tri-methylated on lysine 4 (H3K4Me3). The ING proteins have been involved in the control of cell growth, senescence, apoptosis, chromatin remodeling, and DNA repair. Within the ING family, ING1 and ING2 form a subgroup since they are evolutionarily and functionally close. In yeast, only one gene, Pho23, is related to ING1 and ING2 and possesses also a PHD. Recently, the ING1 and ING2 tumor suppressor status has been fully established since several studies have described the loss of ING1 and ING2 protein expression in human tumors and both ING1 and ING2 knockout mice were reported to have spontaneously developed tumors, B cell lymphomas, and soft tissue sarcomas, respectively. In this review, we will describe for the first time what is known about the ING1 and ING2 genes, proteins, their regulations in both human and mice, and their status in human tumors. Furthermore, we explore the current knowledge about identified functions involving ING1 and ING2 in tumor suppression pathways especially in the control of cell cycle and in genome stability.

Thyroid hormone-dependent development in Xenopus laevis: a sensitive screen of thyroid hormone signaling disruption by municipal wastewater treatment plant effluent

Because thyroid hormones (THs) are conserved modulators of development and physiology, identification of compounds adversely affecting TH signaling is critical to human and wildlife health. Anurans are an established model for studying disruption of TH signaling because metamorphosis is dependent upon the thyroid system. In order to strengthen this model and identify new gene transcript biomarkers for TH disruption, we performed DNA microarray analysis of Xenopus laevis tadpole tail transcriptomes following treatment with triiodothyronine (T(3)). Comparison of these results with previous studies in frogs and mammals identified 36 gene transcripts that were TH-sensitive across clades. We then tested molecular biomarkers for sensitivity to disruption by exposure to wastewater effluent (WWE). X. laevis tadpoles, exposed to WWE from embryo through metamorphosis, exhibited an increased developmental rate compared to controls. Cultured tadpole tails showed dramatic increases in levels of four TH-sensitive gene transcripts (thyroid hormone receptor β (TRβ), deiodinase type II (DIO2), and corticotropin releasing hormone binding protein (CRHBP), fibroblast activation protein α (FAPα)) when exposed to T(3) and WWE extracts. TRβ, DIO2, and CRHBP were identified as TH sensitive in other studies, while FAPα mRNA transcripts were highly TH sensitive in our array. The results validate the array and demonstrate TH-disrupting activity by WWE. Our findings demonstrate the usefulness of cross-clade analysis for identification of gene transcripts that provide sensitivity to endocrine disruption. Further, the results suggest that development is disrupted by exposure to complex mixes of compounds found in WWE possibly through interference with TH signaling.

Modulation of thyroid hormone-dependent gene expression in Xenopus laevis by INhibitor of Growth (ING) proteins

BACKGROUND

INhibitor of Growth (ING) proteins belong to a large family of plant homeodomain finger-containing proteins important in epigenetic regulation and carcinogenesis. We have previously shown that ING1 and ING2 expression is regulated by thyroid hormone (TH) during metamorphosis of the Xenopus laevis tadpole. The present study investigates the possibility that ING proteins modulate TH action.

METHODOLOGY/PRINCIPAL FINDINGS

Tadpoles expressing a Xenopus ING2 transgene (Trans(ING2)) were significantly smaller than tadpoles not expressing the transgene (Trans(GFP)). When exposed to 10 nM 3,5,3'-triiodothyronine (T(3)), premetamorphic Trans(ING2) tadpoles exhibited a greater reduction in tail, head, and brain areas, and a protrusion of the lower jaw than T(3)-treated Trans(GFP) tadpoles. Quantitative real time polymerase chain reaction (QPCR) demonstrated elevated TH receptor β (TRβ) and TH/bZIP transcript levels in Trans(ING2) tadpole tails compared to Trans(GFP) tadpoles while TRα mRNAs were unaffected. In contrast, no difference in TRα, TRβ or insulin-like growth factor (IGF2) mRNA abundance was observed in the brain between Trans(ING2) and Trans(GFP) tadpoles. All of these transcripts, except for TRα mRNA in the brain, were inducible by the hormone in both tissues. Oocyte transcription assays indicated that ING proteins enhanced TR-dependent, T(3)-induced TRβ gene promoter activity. Examination of endogenous T(3)-responsive promoters (TRβ and TH/bZIP) in the tail by chromatin immunoprecipitation assays showed that ING proteins were recruited to TRE-containing regions in T(3)-dependent and independent ways, respectively. Moreover, ING and TR proteins coimmunoprecipitated from tail protein homogenates derived from metamorphic climax animals.

CONCLUSIONS/SIGNIFICANCE

We show for the first time that ING proteins modulate TH-dependent responses, thus revealing a novel role for ING proteins in hormone signaling. This has important implications for understanding hormone influenced disease states and suggests that the induction of ING proteins may facilitate TR function during metamorphosis in a tissue-specific manner.

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.

Apoptosis in amphibian organs during metamorphosis

During amphibian metamorphosis, the larval tissues/organs rapidly degenerate to adapt from the aquatic to the terrestrial life. At the cellular level, a large quantity of apoptosis occurs in a spatiotemporally-regulated fashion in different organs to ensure timely removal of larval organs/tissues and the development of adult ones for the survival of the individuals. Thus, amphibian metamorphosis provides us a good opportunity to understand the mechanisms regulating apoptosis. To investigate this process at the molecular level, a number of thyroid hormone (TH) response genes have been isolated from several organs of Xenopus laevis tadpoles and their expression and functional analyses are now in progress using modern molecular and genetic technologies. In this review, we will first summarize when and where apoptosis occurs in typical larva-specific and larval-to-adult remodeling amphibian organs to highlight that the timing of apoptosis is different in different tissues/organs, even though all are induced by the same circulating TH. Next, to discuss how TH spatiotemporally regulates the apoptosis, we will focus on apoptosis of the X. laevis small intestine, one of the best characterized remodeling organs. Functional studies of TH response genes using transgenic frogs and culture techniques have shown that apoptosis of larval epithelial cells can be induced by TH either cell-autonomously or indirectly through interactions with extracellular matrix (ECM) components of the underlying basal lamina. Here, we propose that multiple intra- and extracellular apoptotic pathways are coordinately controlled by TH to ensure massive but well-organized apoptosis, which is essential for the proper progression of amphibian metamorphosis.

Role of Thiocyanate, Bromide and Hypobromous Acid in Hydrogen Peroxide-induced Apoptosis

We have previously reported that H2O2-induced apoptosis in HL-60 human leukemia cells takes place in the presence of chloride, requires myeloperoxidase (MPO), and occurs through oxidative reactions involving hypochlorous acid and chloramines. We now report that when chloride is replaced by the pseudohalide thiocyanate, there is little or no H2O2-induced apoptosis. Furthermore, thiocyanate inhibits H2O2-induced apoptosis when chloride is present at physiological concentrations, and this occurs at thiocyanate concentrations that are present in human serum and saliva. In contrast, bromide can substitute for chloride in H2O2-induced apoptosis, but results in a lower percent of the cells induced into apoptosis. Hypobromous acid is likely a short-lived intermediate in this H2O2/MPO/bromide apoptosis, and reagent hypobromous acid and bromamines induce apoptosis in HL-60 cells. We conclude that the physiologic concentrations of thiocyanate found in human plasma could modulate the cytototoxicity of H2O2 and its resulting highly toxic MPO-generated hypochlorous acid by competing with chloride for MPO. Furthermore, the oxidative products of the reaction of thiocyanate with MPO are relatively innocuous for human leukemic cells in culture. In contrast, bromide can support H2O2/MPO/halide apoptosis, but is less potent than chloride and it has no effect in the presence of physiological levels of chloride.

ING function in apoptosis in diverse model systems

Genetic studies in model organisms have shown that programmed cell death (apoptosis) plays a significant role during development, where a deficiency in apoptosis results in severe and diverse diseases. Dysregulation of apoptosis also contributes to a variety of human diseases, such as cancer and autoimmune diseases. ING family proteins (ING1-ING5) are involved in many cellular processes, and appear to play a significant role in apoptosis. Loss or downregulation of ING protein function is frequently observed in different tumour types, many of which are resistant to apoptosis, thus warranting their classification as type II tumour suppressors. Several different in vitro and in vivo models have explored the role of ING proteins in regulating apoptosis. In this review, we discuss the progress that has been made in understanding ING protein function in apoptosis using in vitro studies and Mus musculus, Xenopus laevis, and Caenorhabditis elegans experimental models, with an emphasis on ING1 and ING3.

Reprogramming and differentiation in mammals: motifs and mechanisms

The natural reprogramming of the mammalian egg and sperm genomes is an efficient process that takes place in less than 24 hours and gives rise to a totipotent zygote. Transfer of somatic nuclei to mammalian oocytes also leads to their reprogramming and formation of totipotent embryos, albeit very inefficiently and requiring an activation step. Reprogramming of differentiated cells to induced pluripotent stem (iPS) cells takes place during a period of time substantially longer than reprogramming of the egg and sperm nuclei and is significantly less efficient. The stochastic expression of endogenous proteins during this process would imply that controlled expression of specific proteins is crucial for reprogramming to take place. The fact that OCT4, NANOG, and SOX2 form the core components of the pluripotency circuitry would imply that control at the transcriptional level is important for reprogramming to iPS cells. In contradistinction, the much more efficient reprogramming of the mammalian egg and sperm genomes implies that other levels of control are necessary, such as chromatin remodeling, translational regulation, and efficient degradation of no longer needed proteins and RNAs.

Stabilized phosphatidylinositol-5-phosphate analogues as ligands for the nuclear protein ING2: chemistry, biology, and molecular modeling

The interaction of PtdIns(5)P with the tumor suppressor protein ING2 has been implicated in the regulation of chromatin modification. To enhance the stability of PtdIns(5)P for studies of the biological role in vivo, two phosphatase-resistant moieties were used to replace the labile 5-phosphate. The total asymmetric synthesis of the 5-methylenephosphonate (MP) and 5-phosphothionate (PT) analogues of PtdIns(5)P is described herein, and the resulting metabolically stabilized lipid analogues were evaluated in three ways. First, liposomes containing either the dioleoyl MP or PT analogues bound to recombinant ING2 similar to liposomes containing dipalmitoyl PtdIns(5)P, indicating that the replacement of the hydrolyzable 5-phosphate group does not compromise the binding. Second, the dioleoyl MP and PT PtdIns(5)P analogues were equivalent to dipalmitoyl PtdIns(5)P in augmenting cell death induced by a DNA double-strand break in HT1080 cells. Finally, molecular modeling and docking of the MP or PT analogues to the C-terminus PtdInsP-binding region of ING2 (consisting of a PHD finger and a polybasic region) revealed a number of complementary surface and electrostatic contacts between the lipids and ING2.

Characterization of Inhibitor of Growth 2 tumor suppressor in Alligator mississippiensis, its conservation in Archosauria, and response to thyroid stimulating hormone

Inhibitor of growth 2 (ING2) belongs to a family of tumor suppressors that are important regulators of a wide range of cellular processes including proliferation, apoptosis, and DNA repair. ING family members are found in yeast, plants, invertebrates and many vertebrate species. However, to date, ING has not been characterized in reptiles. Herein we describe the isolation of expressed ING2 sequence in the American alligator, Alligator mississippiensis, and compare this sequence with that isolated in the chicken. We identify features that are unique to these two representatives of the Archosaurs including conservation of specific amino acid residues and the absence of an adenylate residue in the 5' end of the nucleotide sequence relative to frogs and mammals. The latter feature results in an alteration of the coding potential leading to distinctive N-termini. Injection of juvenile alligators with thyroid stimulating hormone (TSH), which increases endogenous thyroid hormones, results in the modulation of ING2 transcript levels. Quantitative real time polymerase chain reaction analyses revealed a reduction in the steady-state levels of ING2 mRNA in the phallus/cliterophallus, lung, and liver by 48 h after TSH injection. ING2 expression in the thyroid gland, gonad, and heart was unaffected by TSH treatment. These data indicate that control of ING2 expression by the thyroid axis may be conserved among species and is tissue-dependent.

Decreased cyclin-dependent kinase activity promotes thyroid hormone-dependent tail regression in Rana catesbeiana

The thyroid hormone (TH), 3,5,3'-triiodothyronine (T(3)), is an important regulator of diverse cellular processes including cell proliferation, differentiation, and apoptosis, with increasing evidence that the modulation of the phosphoproteome is an important factor in the TH-mediated response. However, little is understood regarding the mechanisms whereby phosphorylation may contribute to T(3)-mediated cellular outcomes during development. The cyclin-dependent kinases (Cdks) and mitogen-activated protein kinases (MAPK/ERK) have been implicated in TH signaling in mammalian cells. In this study, we have investigated, in frogs, the possible role that these kinases may have in the promotion of tail regression during tadpole metamorphosis, an important postembryonic process that is completely TH-dependent. Cdk2 steady state levels and activity increase in the tail concurrent with progression through the growth phase of metamorphosis, followed by a precipitous decrease coinciding with tail regression. Cyclin-A-associated kinase activity also follows a similar trend except that its associated kinase activity is maintained longer before a decrease in activity. Protein steady state levels of ERK1 and ERK2 remain relatively constant, and their kinase activities do not decrease until much later during tail regression. Tail tips cultured in serum-free medium in the presence of T(3) undergo regression, which is accelerated by coincubation with a specific Cdk2 inhibitor. Coincubation with PD098059, a MAPK inhibitor, has no effect. Thus, T(3)-dependent tail regression does not require MAPKs, but a decrease in Cdk2 activity promotes tail regression.

Genistein prevents thyroid hormone-dependent tail regression ofRana catesbeiana tadpoles by targetting protein kinase C and thyroid hormone receptor α

Thyroid hormone (TH)-regulated gene expression is mainly mediated by TH binding to nuclear thyroid hormone receptors (TRs). Despite extensive studies in mammalian cell lines that show that phosphorylation signaling pathways are important in TH action, little is known about their roles on TH signaling in vivo during development. Anuran metamorphosis is a postembryonic process that is absolutely dependent upon TH and tadpole tail resorption can be precociously induced by exogenous administration of 3,5,3'-triiodothyronine (T(3)). We demonstrate that genistein (a major isoflavone in soy products and tyrosine kinase inhibitor) and the PKC inhibitor (H7) prevent T(3)-induced regression of the Rana catesbeiana tadpole tail. T(3)-induced protein kinase C tyrosine phosphorylation and kinase activity are inhibited by genistein while T(3)-induced up-regulation of TRbeta mRNA, but not TRalpha mRNA, is significantly attenuated, most likely through inhibition of T(3)-dependent phosphorylation of the TRalpha protein. This phosphorylation may be modulated through PKC. These data demonstrate that T(3) signaling in the context of normal cells in vivo includes phosphorylation as an important factor in establishing T(3)-dependent tail regression during development.

Thyroid hormone regulates endogenous amyloid-beta precursor protein gene expression and processing in both in vitro and in vivo models

Thyroid hormone negatively regulates the amyloid-beta precursor protein (APP) gene in thyroid hormone receptor (TR)-transfected neuroblastoma cells. A negative thyroid hormone response element (nTRE) that mediates this regulation has been identified in the first exon of the APP gene. We demonstrate in an in vivo system that expression of APP mRNA, APP protein, and APP secretase cleavage products in mouse brain is influenced by thyroid status. Adult female mice were made hyperthyroid or hypothyroid for 3 weeks and compared to euthyroid mice. APP gene product expression was increased in hypothyroid mouse brain and reduced in hyperthyroid mouse brain, when compared to euthyroid controls. We observed similar effects of thyroid hormone on endogenous APP gene expression in human neuroblastoma cells. The incidence of hypothyroidism increases with age, and localized hypothyroidism of central nervous system has been reported in some patients with Alzheimer's disease (AD). Reduced action of thyroid hormone on the APP gene may contribute to AD pathology by increasing APP expression and the levels of processed APP products. These findings may be an underlying mechanism contributing to the association of hypothyroidism with AD in the elderly, as well as identifying a potential therapeutic target. Pharmacologic supplementation of thyroid hormone, or its analogs, may reduce APP gene expression and beta amyloid peptide accumulation.

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.

Multiple variants of the ING1 and ING2 tumor suppressors are differentially expressed and thyroid hormone-responsive in Xenopus laevis

The tumor suppressor candidate, inhibitor of growth (ING) is implicated in the control of apoptosis, cell cycle progression, chemosensitivity, and senescence. There are at least five different genes in mammals, ING1-ING5, and there is limited evidence that multiple transcript variants exist for ING1 that encode proteins with different functions. No variants have yet been reported for other ING genes. Here, we report the isolation of seven Xenopus laevis (x)ING1 and three xING2 transcript variants and give the first evidence for their independent regulation by thyroid hormone (TH). Comparison with mammalian genes reveals conservation in gene structure. xING1 and xING2 transcript variants are differentially expressed in adult tissues with the greatest number of variants expressed at high levels in brain, testis, and eye. During metamorphosis of the tadpole into a frog, the hindlimb, tail, and brain undergo growth, apoptosis, or remodeling, respectively. We show that xING1 and xING2 transcript variants are significantly reduced in the hindlimb while many variants increase in the tail. These transcript variants remain largely unchanged in the brain during this developmental period. By exposing premetamorphic tadpoles to TH, a precocious metamorphosis is induced. We identify specific variants whose steady state levels are significantly affected by TH at 24 and 48h of exposure. Although several of the variants show expression patterns reminiscent of that observed in natural metamorphosis, the results indicate that additional factors may be involved to influence the steady state transcript levels during development.

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.

Implication ofbaxinXenopus laevistail regression at metamorphosis

Apoptosis is fundamental to normal vertebrate development. A dramatic example of postembryonic development involving apoptosis is tail regression during amphibian metamorphosis. Earlier studies led us to propose a functional role for the pro-apoptotic protein Bax in tadpole tail regression. However, its physiological relevance has never been analyzed. We have now cloned a cDNA encoding Xenopus laevis bax (xlbax) and used in vivo gene transfer in tail muscle to analyze the effects of xlbax overexpression. Furthermore, by using an antisense strategy in a similar experimental paradigm, xlbax antisense mRNA was shown to block the apoptotic effects of xlbax and protect against apoptosis in metamorphosing tadpoles. Our results suggest that xlbax is a regulator of muscle fiber death in the regressing tail during metamorphosis.

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.

ING4 induces G2/M cell cycle arrest and enhances the chemosensitivity to DNA-damage agents in HepG2 cells

The known members of inhibitor of growth (ING) gene family are considered as candidate tumor suppressor genes. ING4, a novel member of ING family, is recently reported to interact with tumor suppressor p53, p300 (a major component of histone acetyl transferase complexes), and p65(RelA) subunit of NF-kappaB. In this study, we investigated the cellular behaviors of HepG2 cells with exogenous ING4. Interestingly, the overexpression of ING4 negatively regulated the cell growth with significant G2/M arrest of cell cycle, and moreover, enhanced the cell apoptosis triggered by serum starvation in HepG2 cells. Furthermore, the exogenous ING4 could upregulate endogenous p21 and Bax in HepG2 cells, not in p53-deficient Saos-2 cells, suggesting that G2/M arrest induced by ING4 could be mediated by the increased p21 expression in a p53-dependent manner, although there is no significant increase of p53 expression in HepG2 cells. Moreover, HepG2 cells with exogenous ING4 could significantly increase cell death, as exposed to some DNA-damage agents, such as etoposide and doxorubicin, implying that ING4 could enhance chemosensitivity to certain DNA-damage agents in HepG2 cells.

Cyclosporin A inhibits thyroid hormone-induced shortening of the tadpole tail through membrane permeability transition

Regression of the tadpole tail through muscule cell apoptosis is one of the most spectacular events in amphibian metamorphosis. Accumulated evidence has shown that mitochondrial membrane permeability transition (MPT) plays a crucial role in apoptosis. Previously we reported that cyclosporin A (CsA) suppressed 3,5,3'-triiodothyronine (T(3))-induced mitochondrial swelling, which was coupled with cytochrome c (Cyt.c) release through MPT [Comp. Biochem. Phys. 130 (2001) 411-418]. To further clarify the mechanism of tadpole metamorphosis, the present study investigates the effect of CsA on T(3) induced tadpole tail shortening. A low concentration of T(3) (5 x 10(-8) M) was found to induce a shortening of stage X Rana rugosa tadpole tails, accompanied by an increase in caspase-3- and -9 like protease activity, as well as an increase in DNA-fragmentation and ladder formation, while CsA was seen to suppress the effects of T(3). The stage X tadpole tail was found to express Bax mRNA and this expression was not affected by T(3) treatment. CsA, on the other hand, proved to have a slightly supressive effection on Bax expression. 20 microM T(3) as well as 50 microM Ca(2+) induced swelling in mitochondria isolated from the liver of R. rugosa resulting in the release of apoptosis related substances, and the released fraction activated cytosolic caspase-3 and -9 in the presence of dATP. This result indicated that Cyt.c might be released from mitochondria by treatment with T(3) through both direct and indirect action of T(3). From these results and other data it was concluded that mitochondrial MPT plays an important role in T(3)-induced apoptosis in the tadpole tail, resulting in tail shortening, and CsA was seen to suppress the effects of T(3).

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.