Interest in the topic of tumour metabolism has waxed and waned over the past century of cancer research. The early observations of Warburg and his contemporaries established that there are fundamental differences in the central metabolic pathways operating in malignant tissue. However, the initial hypotheses that were based on these observations proved inadequate to explain tumorigenesis, and the oncogene revolution pushed tumour metabolism to the margins of cancer research. In recent years, interest has been renewed as it has become clear that many of the signalling pathways that are affected by genetic mutations and the tumour microenvironment have a profound effect on core metabolism, making this topic once again one of the most intense areas of research in cancer biology.

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Regulation of cancer cell metabolism

Epigenetic mechanisms are essential for normal development and maintenance of tissue-specific gene expression patterns in mammals. Disruption of epigenetic processes can lead to altered gene function and malignant cellular transformation. Global changes in the epigenetic landscape are a hallmark of cancer. The initiation and progression of cancer, traditionally seen as a genetic disease, is now realized to involve epigenetic abnormalities along with genetic alterations. Recent advancements in the rapidly evolving field of cancer epigenetics have shown extensive reprogramming of every component of the epigenetic machinery in cancer including DNA methylation, histone modifications, nucleosome positioning and non-coding RNAs, specifically microRNA expression. The reversible nature of epigenetic aberrations has led to the emergence of the promising field of epigenetic therapy, which is already making progress with the recent FDA approval of three epigenetic drugs for cancer treatment. In this review, we discuss the current understanding of alterations in the epigenetic landscape that occur in cancer compared with normal cells, the roles of these changes in cancer initiation and progression, including the cancer stem cell model, and the potential use of this knowledge in designing more effective treatment strategies.

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Epigenetics in Cancer

Irrespective of the morphological features of end-stage cell death (that may be apoptotic, necrotic, autophagic, or mitotic), mitochondrial membrane permeabilization (MMP) is frequently the decisive event that delimits the frontier between survival and death. Thus mitochondrial membranes constitute the battleground on which opposing signals combat to seal the cell's fate. Local players that determine the propensity to MMP include the pro- and antiapoptotic members of the Bcl-2 family, proteins from the mitochondrialpermeability transition pore complex, as well as a plethora of interacting partners including mitochondrial lipids. Intermediate metabolites, redox processes, sphingolipids, ion gradients, transcription factors, as well as kinases and phosphatases link lethal and vital signals emanating from distinct subcellular compartments to mitochondria. Thus mitochondria integrate a variety of proapoptotic signals. Once MMP has been induced, it causes the release of catabolic hydrolases and activators of such enzymes (including those of caspases) from mitochondria. These catabolic enzymes as well as the cessation of the bioenergetic and redox functions of mitochondria finally lead to cell death, meaning that mitochondria coordinate the late stage of cellular demise. Pathological cell death induced by ischemia/reperfusion, intoxication with xenobiotics, neurodegenerative diseases, or viral infection also relies on MMP as a critical event. The inhibition of MMP constitutes an important strategy for the pharmaceutical prevention of unwarranted cell death. Conversely, induction of MMP in tumor cells constitutes the goal of anticancer chemotherapy.

Mitochondrial Membrane Permeabilization in Cell Death

The regulation of cell growth and survival can be subverted by a variety of genetic defects that alter transcriptional programs normally responsible for controlling cell number. High throughput analysis of these gene expression patterns should ultimately lead to the identification of minimal expression profiles that will serve as common denominators in assigning a cancer to a given category. In the course of defining the common denominators, though, we should not be too surprised to find that cancers within a single category may nevertheless exhibit seemingly disparate genetic defects. The wnt pathway has already provided an outstanding example of this. We now know of three regulatory genes in this pathway that are mutated in primary human cancers and several others that promote experimental cancers in rodents (Fig. 1). In all of these cases the common denominator is the activation of gene transcription by -catenin. The resulting gene expression profile should provide us with a signature common to those cancers carrying defects in the wnt pathway. In this review, the wnt pathway will be covered from the perspective of cancer, with emphasis placed on molecular defects known to promote neoplastic transformation in humans and in animal models.

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Wnt signaling and cancer

Beneath the complexity and idiopathy of every cancer lies a limited number of 'mission critical' events that have propelled the tumour cell and its progeny into uncontrolled expansion and invasion One of these is deregulated cell proliferation, which, together with the obligate compensatory suppression of apoptosis needed to support it, provides a minimal 'platform' necessary to support further neoplastic progression Adroit targeting of these critical events should have potent and specific therapeutic consequences

Proliferation, cell cycle and apoptosis in cancer

Aims: Mounting evidence indicates that deregulation of apoptosis is involved in the mechanisms of cancer development. Integrins are cell adhesion receptors that mediate cell survival and migration. A recent study showed that unligated integrin beta 3 (ITGB3) induced apoptosis by recruitment of caspase-8. The aim of the present study was to explore the possibility that genetic alteration of the ITGB3 gene is involved in the development of human cancers possibly by inactivating the apoptosis function of ITGB3. Methods: We analyzed the coding region of the cytoplasmic domain of the human ITGB3 gene for the detection of somatic mutations in 100 gastric, 90 colorectal, 100 non-small cell lung, 43 urinary bladder and 50 head-neck cancers by a polymerase chain reaction-based, single-strand conformation polymorphism. Results: We found an identical ITGB3 mutation in two unrelated patient samples (one in colorectal and the other in bladder cancer). The ITGB3 mutation was a missense mutation which would substitute an amino acid (E757K). Conclusions: The data suggested that the proapoptotic ITGB3 cytoplasmic domain is rarely mutated in common human cancers and may not play an important role in the development of the cancers.

/pdf/mutational-analysis-of-proapoptotic-integrin-beta-3-2odd5ky9wb.pdf

Mutational analysis of proapoptotic integrin beta 3 cytoplasmic domain in common human cancers.

Mounting evidence indicates that deregulation of apoptosis contributes to the development of human cancers. BAD, a proapoptotic Bcl-2 family protein, regulates the intrinsic apoptosis pathway. The aim of this study was to explore whether alterations of phospho-BAD (p-BAD) protein that antagonizes apoptosis function of BAD and mutation of BAD gene are characteristics of human gastric cancers. We analyzed expression of p-BAD in 60 gastric adenocarcinomas by immunohistochemistry. Also, we analyzed BAD gene for detection of somatic mutations by single-strand conformation polymorphism (SSCP) assay. p-BAD expression was detected well in normal gastric mucosal epithelial cells, whereas it was detected in only 51% (31 of the 60) of the cancers. There was no somatic mutation of BAD gene in the 60 gastric cancer samples. The decreased expression of p-BAD in malignant gastric epithelial cells compared to normal mucosal epithelial cells suggested that loss of p-BAD expression may play a role in gastric tumorigenesis. The data also suggest that BAD mutation may not be a direct target of inactivation in gastric tumorigenesis.

Immunohistochemical analysis of phospho‐BAD protein and mutational analysis of BAD gene in gastric carcinomas

Dyskeratosis congenita is a genetic disease caused by point muations in the DKC1 gene [1]. Patients with dyskeratosis congenita show bone marrow failure syndrome characterized by abnormal skin pigmentation and mucosal leukoplakia [2]. Of note, a subset of patients with dyskeratosis congenita developed malignant tumors of various histologic origins [2]. Also, DKC1 mutant mice were highly susceptible to tumor development, and the most common tumors were lung and breast tumors [3]. These observations suggested that DKC1 may be a tumor suppressor gene. DKC1 protein normally binds with small nucleolar RNAs and the RNA components of telomerase, and these functions are impaired in the cells of the DKC1 mutant mice [3]. In the individuals with dyskeratosis congenita, DKC1 gene mutation is detected usually in the exon 3, strongly suggesting that these mutations may related with the disease phenotypes [1,4,5]. It could be hypothesized that increased incidence of malignant tumors in the dyskeratosis congenita patients might be related to the DKC1 mutations. It is of interest to see whether the DKC1 gene is somatically mutated in human cancers. However, to date, the data on the somatic mutations of DKC1 in human sporadic cancers is lacking. The aim of this study was to see whether common human sporadic cancers harbor DKC1 mutation. We have analyzed methacarn-fixed tissues of 140 gastric carcinomas, 104 colorectal carcinomas, 94 breast ductal carcinomas, 100 non-small cell caners and 69 hepatocellular carcinomas. All of the patients of the cancers were Asians (Koreans). The gastric carcinomas consisted of 60 diffuse-type, 49 intestinal-type and 31 mixed-type gastric adenocarcinomas by Lauren’s classification, and 25 early and 115 advanced gastric carcinomas according to the depth of invasion. The colorectal carcinomas originated from cecum (n /2), ascending colon (n /19), transverse colon (n /6), descending colon (n /4), sigmoid colon (n /28) and rectum (n /45). The breast carcinomas consisted of 15 intraductal and 79 invasive ductal carcinomas. The non-small cell lung cancer samples consisted of 50 adenocarcinomas, 47 squamous cell carcinomas, 1 adenosquamous carcinomas and 2 large cell carcinomas. The hepatocellular carcinomas consisted of Edmondson grade I (n /8), grade II (n /30) and grade III (n / 31) according to Edmondson and Steiner’s criteria [6]. Malignant cells and normal cells from the same patients were selectively procured from hematoxylin and eosin-stained slides using a 30G1/2 hypodermic needle (Becton Dickinson, Franklin Lakes, NJ) affixed to a micromanipulator, as described previously [7]. DNA extraction was performed by a modified single-step DNA extraction method [7]. Because the most common site of the germline mutations of DKC1 was reported to be the exon 3 [1,4,5], we analyzed the exon 3 in this study. Genomic DNA each from tumor cells and corresponding normal cells were amplified with a primer pair covering the DNA sequences in the exon 3. For the detection of DKC1 mutations, we analyzed the exon by

Absence of DKC1 exon 3 mutation in common human cancers

CUB and Sushi multiple domains 1 (CSMD1) is mapped to chromosome 8p23 that is frequently deleted in head and neck cancers [1]. Decreased expression of CSMD1 is also common in lung, breast, head/neck and skin cancers [2]. Structure-specific endonuclease subunit (SLX4) encodes a Fanconi anemia-related protein that is required for repair of specific types of DNA lesions and critical for cellular responses to replication fork failure [3]. SLX4 interaction with SUMO plays an important role in maintenance of genome [4], instability of which is a key feature of cancer. Together, these data suggest that both CSMD1 and SLX4 might have tumor suppressor gene (TSG) activities in cells [1,2.4]. However, it remains unknown whether inactivating frameshift mutations of their inactivating mutations are common in colorectal cancer (CRC). About 10–20% third of CRC are classified as high microsatellite instability (MSI-H) cancers [5]. Lots of TSGs harbor frameshift mutations at monocleotide repeats in MSI-H cancers [5]. In the human genome database, we observed that both CSMD1 and SLX4 genes possess nucleotide repeats in coding sequences that might be mutated in MSI-H cancers. In this study, we analyzed a T7 repeat in CSMD1 and a C7 repeat in SLX4 by polymerase chain reaction (PCR)-based single strand conformation polymorphism (SSCP) assay. In this study, we used 124 CRCs. The CRCs were 79 CRCs with MSI-H and 45 CRCs with microsatellite stable (MSS). In cancer tissues, malignant cells and normal cells were selectively procured by microdissection [6]. Radioisotope ([P]dCTP) was incorporated into the PCR products, which were subsequently displayed in SSCP gels and analyzed with direct DNA sequencing [6]. On SSCP, we observed aberrant bands of CSMD1 in one case of CRCs and SRPK1 in two cases of CRCs. Sanger sequencing of them revealed that they were frameshift mutations of CSMD1 and SLX4 (Fig. 1). DNA from the patients’ normal tissues showed no evidence of mutation in both SSCP and Sanger sequencing, indicating the mutations had risen somatically. These mutations were all deletions of one base in the T7 repeat of CSMD1 (c.9722delT) and the C7 repeat of SLX4 (c.140delC) that would result in frameshift mutations (p.Phe3241SerfsX21 of CSMD1 and p.Pro469HisfsX4 of SLX4) (Fig. 1). They were detected in two CRCs (3/79: 3.8%) with MSI-H, but not in those with MSS (0/45). The frameshift mutations of CSMD1 and SLX4 detected in the present study would result in premature stops of amino acid synthesis in CSMD1 and SLX4 proteins, respectively, and hence resemble a typical inactivating mutation. Based on the earlier data that showed TSG activities of PLA2R1

Nam Jin Yoo

Papers

Mutational analysis of proapoptotic integrin beta 3 cytoplasmic domain in common human cancers.

Immunohistochemical analysis of phospho‐BAD protein and mutational analysis of BAD gene in gastric carcinomas

Absence of DKC1 exon 3 mutation in common human cancers

Rare frameshift mutations of putative tumor suppressor genes CSMD1 and SLX4 in colorectal cancers.

NSD1 encoding a histone methyltransferase exhibits frameshift mutations in colorectal cancers