Dynamics of cell interactions and communications during melanoma development

Melanoma development not only involves genetic and epigenetic changes that take place within the cell, but also involves processes determined collectively by micro-environmental factors, including cell-cell interactions and communications. During the transition from normal cells to benign and malignant lesions, and subsequently to metastatic cancer, stepwise changes in intercellular communications provide tumor cells with the ability to overcome cell-cell adhesion and micro-environmental controls from the host and to invade surrounding tissues and disperse to distant locations. Cadherins are major cell-cell adhesion molecules involved in the development and maintenance of skin. E-cadherin expressed in normal melanocytes mediates growth and invasion control by keratinocytes. Progressive loss of E-cadherin and gain of N-cadherin during melanoma development not only free melanoma cells from control by keratinocytes, but also provide new adhesion properties, resulting in switched partnerships with fibroblasts and vascular endothelial cells. The cadherin subtype switching also dictates gap junctional specificity in melanocytic cells during tumor development. This selective intercellular communication may contribute to the regulation of cell growth, differentiation, apoptosis, and migration of melanocytic cells in both physiologic and pathologic conditions. Abnormal up-regulation of the immunoglobin repeat-containing cell adhesion molecules Mel-CAM and L1-CAM potentiates invasion and migration of melanoma. Thus, abnormal expression of intercellular adhesion receptors and dysregulated intercellular communication underlies melanoma development and progression.

Verapamil modulates LPS-induced cytokine production via inhibition of NF-kappa B activation in the liver

OBJECTIVE

To investigate the effect of verapamil on Lipopolysaccharide (LPS)-induced cytokines [tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6) and interleukin-10 (IL-10)] and nuclear factor kappa B (NF-kappa B) in the liver.

METHODS AND MATERIALS

Adult male Sprague-Dawley rats were randomly divided into seven groups of eight rats each: control rats treated with saline (0.9 % NaCl); rats treated with saline and then challenged intraperitoneally with LPS (10 mg/kg); rats treated intraperitoneally with different levels of verapamil (1, 2.5, 5, 10 mg/kg) and then challenged with LPS (10 mg/kg); and rats treated only with verapamil (10 mg/kg). TNF-alpha, IL-6, IL-10 and NF-kappa B in the liver tissues were investigated as well as the serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) one hour after LPS injection.

RESULTS

LPS alone stimulated production of TNF-alpha, IL-6 and IL-10, and activated NF-kappa B in the liver. Pretreatment with verapamil before LPS challenge reduced acute liver injury, down-regulated production of LPS-induced pro-inflammatory cytokines (TNF-alpha and IL-6), up-regulated production of anti-inflammatory cytokines (IL-10) and inhibited NF-kappa B activation in the liver in a dose-dependent manner.

CONCLUSION

Verapamil can attenuate acute liver injury by down-regulating the production of TNF-alpha and IL-6 and up-regulating IL-10 in the liver, possibly via inhibition of NF-kappa B.

Semimetal-to-semimetal charge density wave transition in 1T-TiSe(2)

We report an infrared study on 1T-TiSe(2), the parent compound of the newly discovered superconductor Cu(x)TiSe(2). Previous studies of this compound have not conclusively resolved whether it is a semimetal or a semiconductor-information that is important in determining the origin of its unconventional charge density wave (CDW) transition. Here we present optical spectroscopy results that clearly reveal that the compound is metallic in both the high-temperature normal phase and the low-temperature CDW phase. The carrier scattering rate is dramatically different in the normal and CDW phases and the carrier density is found to change with temperature. We conclude that the observed properties can be explained within the scenario of an Overhauser-type CDW mechanism.

Measurement of psi2S radiative decays

Using 14 x 10(6) psi(2S) events accumulated at the BESII detector, we report first measurements of branching fractions or upper limits for psi(2S) decays into gammapp, gamma2(pi+pi-), gammaKS0K+pi-+c.c., gammaK+K-pi+pi-, gammaK*0K-pi++c.c., gammaK*0K*0, gammapi+pi-pp, gamma2(K+K-), gamma3(pi+pi-), and gamma2(pi+pi-)K+K- with the invariant mass of hadrons below 2.9 GeV/c2. We also report branching fractions of psi(2S) decays into 2(pi+pi-)pi0, omegapi+pi-, omegaf2(1270), b1+/-pi-/+, and pi02(pi+pi-)K+K-.

Molecular cloning, nucleotide sequencing, and expression of genes encoding alcohol dehydrogenases from the thermophile Thermoanaerobacter brockii and the mesophile Clostridium beijerinckii

Proteins play a pivotal role in thermophily. Comparing the molecular properties of homologous proteins from thermophilic and mesophilic bacteria is important for understanding the mechanisms of microbial adaptation to extreme environments. The thermophile Thermoanaerobacter (Thermoanaerobium) brockii and the mesophile Clostridium beijerinckii contain an NADP(H)-linked, zinc-containing secondary alcohol dehydrogenase (TBADH and CBADH) showing a similarly broad substrate range. The structural genes encoding the TBADH and the CBADH were cloned, sequenced, and highly expressed in Escherichia coli. The coding sequences of the TB adh and the CB adh genes are, respectively, 1056 and 1053 nucleotides long. The TB adh gene encoded an amino acid sequence identical to that of the purified TBADH. Alignment of the deduced amino acid sequences of the TB and CB adh genes showed a 76% identity and a 86% similarity, and the two genes had a similar preference for codons with A or T in the third position. Multiple sequence alignment of ADHs from different sources revealed that two (Cys-46 and His-67) of the three ligands for the catalytic Zn atom of the horse-liver ADH are preserved in TBADH and CBADH. Both the TBADH and CBADH were homotetramers. The substrate specificities and thermostabilities of the TBADH and CBADH expressed inE. coli were identical to those of the enzymes isolated from T. brockii and C. beijerinckii, respectively. A comparison of the amino acid composition of the two ADHs suggests that the presence of eight additional proline residues in TBADH than in CBADH and the exchange of hydrophilic and large hydrophobic residues in CBADH for the small hydrophobic amino acids Pro, Ala, and Val in TBADH might contribute to the higher thermostability of the T. brockii enzyme.

Lean rats with hypothalamic pro-opiomelanocortin overexpression exhibit greater diet-induced obesity and impaired central melanocortin responsiveness

AIMS/HYPOTHESIS

Central pro-opiomelanocortin (Pomc) gene therapy ameliorates genetic- or age-related obesity. We hypothesised that this treatment would delay or prevent dietary obesity in young, lean rats.

MATERIALS AND METHODS

Recombinant adeno-associated virus encoding Pomc (rAAV-Pomc) was delivered bilaterally into the basomedial hypothalamus of lean rats for 42 days. Food intake, body weight, serum hormones, brown adipose tissue (BAT) uncoupling protein 1 (UCP1) and mRNA levels of hypothalamic neuropeptides and melanocortin receptors were assessed. Beginning on day 43, half of the rats remained on chow while the others received a high-fat diet for 89 days. We examined energy balance and responsiveness to the melanocortin agonist melanotan II (MTII) or the antagonist SHU9119.

RESULTS

Pomc gene delivery produced elevated hypothalamic Pomc mRNA (fourfold) and alpha-melanocyte-stimulating hormone levels in the arcuate nucleus (twofold). Food intake and body weight were not altered by rAAV-Pomc in rats fed standard-chow. In rAAV-Pomc rats at day 42, perirenal fat and serum leptin decreased but overall visceral adiposity did not; expression of the hypothalamic agouti-related protein (Agrp) mRNA was elevated, whereas expression of melanocortin 3 and 4 receptor mRNA was reduced; BAT UCP1 protein increased nearly fourfold. The rAAV-Pomc rats fed the high-fat diet consumed more energy and gained more body weight compared with chow- or high-fat-fed controls that did not receive Pomc gene delivery. The anorexic response to MTII was impaired, whereas the orexigenic effect of SHU9119 was enhanced by rAAV-Pomc pretreatment.

CONCLUSIONS/INTERPRETATION

Delivery of the Pomc gene alters energy homeostasis in lean rats, predisposing them to diet-induced obesity. Diminished hypothalamic melanocortin receptors, increased Agrp expression, and potential rewiring of brain circuits may underlie the exacerbated obesity.

MN/CA9: a potential gene marker for detection of malignant cells in effusions

Many cancers cause malignant effusions. The presence of malignant cells in effusions has implications in diagnosis, tumour staging and prognosis. The detection of malignant cells currently presents a challenge for cytopathologists. New adjunctive methods are needed. Although the effusions provide excellent materials for molecular assay, the available molecular markers are extremely limited, which hinders its clinical application. MN/CA9 has proved to be a valuable marker in many cancers such as lung, breast, colon, kidney, etc. The present study was to evaluate MN/CA9 as a new molecular marker for the detection of cancer cells in pleural effusions. Seventy-one pleural effusions including 59 malignant effusions from patients with cancer, and 12 patients with benign diseases as a control, were subjected to RT-PCR for detection of MN/CA9 gene expression. MN/CA9 gene expression was detected in 53/59 (89.8%) pleural effusions from cancer patients (15/16 for breast cancers, 10/11 for lung cancers, 4/4 for ovary cancers, 2/3 for colon-rectal cancers, 5/6 for cancers of unknown site, 7/8 for mesothelioma and 10/11 for other cancers). Furthermore, MN/CA9 was positive in 13/18 (72.2%) of cytologically negative effusions of cancer patients. MN/CA9 was detected in only 1/12 (8.3%) effusions from the control patients (p < 0.01). The sensitivity and specificity of MN/CA9 gene expression were, respectively, 89.8% and 91.7%. Our preliminary results suggest that MN/CA9 could be a potential marker for the detection of malignant cells in effusions. A large-scale study is needed to confirm these results.

Melatonin reduced volume of cerebral infarct induced by photothrombosis in wild-type mice, not in Cyclooxygenase-1 gene knockout mice

Cyclooxygenase (COX) is crucial in inflammation and plays important role in cerebral ischemia. Antiinflammatory effects of melatonin have been verified in previous studies. In this study, cerebral blood flow (CBF) was monitored during operation, infarct volume (IFV) was determined with 5-triphenyltetrazolium chloride (TTC) staining and MR image, and neurological functions were evaluated with turn in an alley and fall pole test in both COX1-gene knockout and wide-type mice with or without melatonin administration 3 days after photothrombosis. CBF reduction, IFV and neurological deficits were not significantly different in COX-1 wild-type and COX-1 knockout mice. Melatonin (15 mg/kg) intraperitoneal injection decreased the CBF reduction, IFV and the latency to turn in an alley in COX-1 wide-type mice, whereas the neuroprotective effect of melatonin was attenuated in COX-1 knockout mice. We concluded that melatonin reduced susceptibility to photothrombotic stroke. COX-1 gene knockout does not alter the susceptibility to cerebral ischemia caused by photothrombosis. COX-1 plays an important role in the pathway of the protection of melatonin.

Significance of HIF-1-active cells in angiogenesis and radioresistance

Human solid tumors contain hypoxic regions that have considerably lower oxygen tension than the normal tissues. Hypoxia offers resistance to radiotherapy and anticancer chemotherapy, as well as predispose to increased tumor metastases. Furthermore, hypoxia induces hypoxia-inducible factor-1 (HIF-1), which in turn increases tumor angiogenesis. Thus, eradication of HIF-1-active/hypoxic tumor cells is very important for cancer therapy. We have previously reported that procaspase-3 fused with a von Hippel-Lindau (VHL)-mediated protein destruction motif of alpha subunit of HIF-1 (HIF-1alpha) containing Pro564, named TAT-ODD-procaspase-3 (TOP3), specifically induced cell death to hypoxic cells in vivo as well as in vitro. We now report that TOP3 also eradicates the radiation-induced HIF-1-active tumor cells. HIF-1 activity in the xenografts of human tumor cells, which express luciferase under the transcriptional control of HIF-1, were monitored and quantified daily with an in vivo bioluminescence photon-counting device. HIF-1 activity in tumors was more rapidly increased by ionizing radiation (IR) compared to untreated tumors. TOP3 efficiently decreased the HIF-1-activity in irradiated tumors as well as unirradiated ones, indicating TOP3 eradicated tumor cells with HIF-1-activity induced by IR as well as hypoxia. Eradication of HIF-1-active/hypoxic cells in the xenografts during irradiation exhibited significant suppression in angiogenesis and strong enhancement in a long-term growth suppression of tumor xenografts. These results further strengthen the argument that HIF-1-active/hypoxic cells play crucial roles in angiogenesis and radioresistance.

Genetic polymorphisms involved in toxicant-metabolizing enzymes and the risk of chronic benzene poisoning in Chinese occupationally exposed populations

Benzene is a recognized haematotoxin and leukaemogen, but its mechanism of action and the role of genetic susceptibility are still unclear. Cytochrome P450 2E1 (CYP2E1) and myeloperoxidase (MPO) are involved in benzene activation; and NAD (P)H:quinine oxidoreductase 1 (NQO1), glutathione S-transferase theta 1 (GSTT1) and glutathione S-transferase mu 1 (GSTM1) participate in benzene detoxification. The common, well-studied single-nucleotide polymorphisms (SNPs) were analysed in these genes drawn from the toxicant-metabolizing pathways. A total of 100 workers with chronic benzene poisoning (CBP) and 90 controls were enrolled in China. There was a 2.82-fold (95% CI = 1.42-5.58) increased risk of CBP in the subjects with the NQO1 609C > T mutation genotype (T/T) compared with those carrying heterozygous (C/T) and wild-type (C/C). The subjects with the GSTT1 null genotype had a 1.91-fold (95% CI = 1.05-3.45) increased risk of CBP compared with those with GSTT1 non-null genotype. There was no association of CYP2E1 and MPO genotype with CBP. A three genes' interaction showed that there was a 20.41-fold (95% CI = 3.79-111.11) increased risk of CBP in subjects with the NQO1 609C > T T/T genotype and with the GSTT1 null genotype and the GSTM1 null genotype compared with those carrying the NQO1 609C > T C/T and C/C genotype, GSTT1 non-null genotype, and GSTM1 non-null genotype. The study provides evidence of an association of a gene-gene interaction with the risk of CBP.

Human ovarian tumour-derived chaperone-rich cell lysate (CRCL) elicits T cell responses in vitro

Tumour-derived chaperone-rich cell lysate (CRCL), which is made up of numerous heat shock proteins, has been used successfully to generate tumour-specific T cell responses and protective immunity against a wide range of murine tumours. In this study, we have investigated the potency of human ovarian cancer-derived CRCL to activate dendritic cells (DC) and to generate tumour-specific T cells in vitro. CRCL was generated from primary ovarian cancers and SKOV3-A2, a HER2/neu, Wilm's tumour gene 1 (WT1) and human leucocyte antigen (HLA)-A2 positive human ovarian tumour cell line. Peripheral blood mononuclear cells from both HLA-A2(+) healthy donors and HLA-A2(+) ovarian cancer patients were stimulated weekly with autologous DC loaded with ovarian tumour-derived CRCL. After four to six stimulations in vitro, specific cytokine secretion and cytotoxicity were measured. CRCL promoted interleukin (IL)-12 secretion and enhanced the immunostimulatory capacity of DC. T cells from healthy controls and from ovarian cancer patients secreted higher amounts of interferon-gamma following in vitro restimulation with ovarian cancer-derived CRCL than with HER2/neu or WT1 peptide-pulsed DC. We were also able to generate cytotoxic T lymphocyte activity against cancer-specific antigens such as HER2/neu and WT1 from all healthy donors, but from only one of the four ovarian cancer patients with bulky disease. These preliminary results substantiate further the concept that CRCL may prove to be a potent adjuvant for women suffering from ovarian cancer and that this personalized vaccine may be a promising approach for active immunotherapy.

S100A1: a powerful marker to differentiate chromophobe renal cell carcinoma from renal oncocytoma

AIMS

The common subtypes of renal tumours are conventional, papillary, chromophobe carcinoma and oncocytoma. The morphological differentiation between chromophobe carcinoma and oncocytoma may be difficult. The aim was to evaluate S100A1 as a new marker for the differentiation of the two subtypes.

METHODS AND RESULTS

Thirty-nine tumour samples [nine clear cell renal cell carcinomas (RCCs), six papillary RCCs, nine chromophobe RCCs and 15 oncocytomas] were studied. The protein expression of S100A1 was evaluated by immunohistochemistry. The gene expression of S100A1 was analysed by reverse transcriptase-polymerase chain reaction. Nine oncocytomas showed strong immunoreactivity for S100A1. Four oncocytomas were scored as moderate and one as weak reactivity. In total, 14/15 (93%) of oncocytomas were considered to be immunopositive. In contrast, all nine chromophobe RCCs were considered to be immunonegative. There was a significant difference in the positive percentages of staining of S100A1 between these two subtypes (P < 0.01). S100A1 immunoreactivity was observed in 6/9 clear cell and 4/6 papillary carcinomas. The results of S100A1 gene expression corresponded well with the results of immunohistochemistry.

CONCLUSION

S100A1 may be a potentially powerful marker to differentiate the chromophobe RCC from renal oncocytoma.

Shear waves induced by moving needle in MR elastography

Magnetic resonance elastography (MRE) is a phase contrast-based method for observing shear wave propagation in a material to determine its stiffness. The objective of this study was to determine whether shear waves suitable for MRE could be induced using a moving acupuncture needle. Tissue-simulating bovine gel phantom and a 0.4 mm diameter acupuncture needle were used in the experiment. The results showed that observable shear waves could be induced in the gel phantom by cyclic needle motion. The observed wavelength varied with excitation frequency, as expected. Generating shear waves using moving needles may be a useful tool to study the basic mechanism of acupuncture with MRE. Further study will be conducted to observe the wave motion in inhomogeneous media and acupuncture-induced effects in in-vivo studies.

Detection of proximal caries with high-resolution and standard resolution digital radiographic systems

AIMS

The aim of this study was to: (1) compare the diagnostic accuracy of the high-resolution and standard resolution settings of four digital imaging systems for caries diagnosis and (2) compare the effect on the diagnostic accuracy of reducing the high-resolution image sizes to the standard resolution dimensions, and vice versa.

MATERIALS AND METHODS

90 extracted human premolars were mounted in groups of 5 in plaster blocks, containing 4 test teeth and 1 non-test tooth. Two blocks at a time were placed in a jig to simulate a bitewing radiograph. Radiographs were taken using four digital systems (Planmeca Dixi 2; Gendex Visualix HDI; Dürr Vistascan; Digora Optime), each at two resolution settings. Next, the teeth were sectioned and a total of 65 surfaces were incorporated in the study. Additionally, the bicubic interpolation method was applied to reduce the high-resolution original images and to enlarge the standard resolution images. The original, reduced and enlarged images were randomly shown to five observers in two random sessions. The observers were asked to assess caries depth on a 4-point scale. The observers' scores were compared with the results from a histological examination. Data were analysed using the statistical theory for multivariate discrete data. Cohen's kappa was used to determine the agreement with the gold standard.

RESULTS

None of the comparisons between the spatial resolution settings, or the comparisons between increased or reduced image size and the original image sizes, showed significant differences in the probability of caries detection (chi2=26.59, df=26, P approximately 0.50). The four digital systems used in this study differ significantly in the probability of caries detection (chi2=41.55, df=24, P<0.02). Compared with the gold standard, the Gendex Visualix HDI CCD sensor has the highest measure of agreement (kappa=0.31).

CONCLUSION

Caries diagnosis does not improve when using high-resolution settings compared with the standard settings. The use of bicubic convolution interpolation for zooming has no detectable effect on caries diagnosis and therefore is recommended to use when enlarging or reducing radiographs. The probability of caries detection, however, was different for the sensor systems of the different manufacturers.

Detection of Proximal Caries in vitro Using Standard and Task-Specific Enhanced Images from a Storage Phosphor Plate System

Eight dentists evaluated 72 proximal surfaces of premolars with respect to all caries lesions and to lesions into dentine in digital images from a storage phosphor plate system. The images were processed in four different ways: (1) the default algorithm of the standard imaging system (DF); (2) an algorithm correcting for attenuation and visual response (AV), and two proprietary caries-specific enhancement algorithms (3) K1, and (4) K2, respectively. The lesions were validated by histological examination. There were no significant differences in the areas under the receiver operating characteristic curves between differently processed radiographs for the categories of all caries lesions and caries into dentine.

Analysis of alpha-fetoprotein mRNA level on the tumor cell hematogenous spread of patients with hepatocellular carcinoma undergoing orthotopic liver transplantation

The aim of this study was to detect alpha-fetoprotein (AFP) mRNA levels in the preoperative and intraoperative peripheral blood of patients with hepatocellular carcinoma (HCC) receiving orthotopic liver transplantation (OLT).

METHODS

We detected AFP mRNA by TaqMan real-time reverse transcriptase-polymerase chain reactions (RT-PCR) on the peripheral blood cells (PBCs) from 30 HCC patients undergoing OLT.

RESULTS

In RT-PCR, fluorescence was undetectable in any control. The positive expression rate of AFP mRNA was 23% (7 of 30) in PBC samples of OLT patients preoperatively and 50% (15 of 30) just before hepatectomy during the operation. The positive rate of AFP mRNA in OLT patients at this time was higher than that at preoperation, a difference that was statistically significant (P < .01).

CONCLUSION

The OLT operation induced release of cells from the liver into the peripheral blood circulation. This may be an important mechanism of liver cancer cell dissemination deserving further investigation.

Emergence of VanD-type vancomycin-resistant Enterococcus faecium in Stockholm, Sweden

A vancomycin-resistant Enterococcus faecium isolate from the urine of a liver transplant patient in Stockholm was found to contain a vanD gene. The sequence of the vanD PCR product shared 100% identity with the vanD5 allele. The isolate was resistant to a relatively high level of vancomycin (128 mg/L) and a low level of teicoplanin (4 mg/L). This is the first VanD-type vancomycin-resistant E. faecium isolate reported in Sweden. The emergence of this strain reinforces the necessity of infection control efforts to interrupt the spread of these organisms.

Association of tightly locked occlusion with temporomandibular disorders

The association between teeth loss and temporomandibular disorders (TMD) is still inconclusive. A kind of secondary changes of the occlusion after teeth lose called the tightly locked occlusion (TLO), defined as the occluding contact that delivers angled occlusal force on the drifted neighbour and/or the tipped antagonists of the lost posterior teeth, was hypothesized to be association with TMD. The study aimed at investigating the association between the TLO and TMD. A total of 113 posterior-teeth losing patients, 64 with TMD symptoms (group of TMD) and 49 without (group of TMD-Free) were included. Study casts and joint radiographs were made to diagnose the TLO and joint morphological changes. The simultaneous contribution of the potential variables of gender, age, tooth losing number, the TLO, joint symmetry and signs of osteoarthrosis shown on radiographs were tested through binary logistic regression analysis. In women, the TLO entered into logistic model, and had an effect on the incidence of TMD (P = 0.008). The odds ratio of with-TLO versus without-TLO is 2.6 (95% CI: 1.2, 5.8) after controlling for the effect of gender. Age, tooth lose number, joint asymmetry or osseous changes had no effect on the incidence of TMD. The tightly locked occlusion is associated with some signs and symptoms of TMD. Randomized controlled trials will be needed in further studies to test the hypothesis that treatment of a TLO, as defined in the present study, will have a beneficial effect on the signs and symptoms of TMD.

Study on the error in the dynamic spectrum method relative with the pathlength factor as a function of wavelength

Utilizing near-infrared spectroscopy for non-invasive blood component concentration sensing has been a focusing topic in biomedical optics applications. The ease of use, low cost and portability of these methods is a clear advantage over the invasive blood component concentration sensing which is the main sensing method in the clinic application. However, there is no report about any successful non-invasive blood components (except the artery blood oxygen saturation) concentration detection techniques that can meet the requirements of clinic application. One of the most key difficulties is the influence of the individual discrepancy. Dynamic spectrum (DS) is a new measure method of non-invasive blood components concentration sensing presented recently. It can eliminate the individual discrepancy of the tissues except the pulsatile component of the artery blood (PCAB) theoretically. This indicates a brand new way to measure the blood components concentration and a potential to provide absolute quantitation of hemodynamic variables. One of the systematic errors in the calculation of the component changes from NIRS data of the dynamic spectrum is the absolute magnitudes and relative differences in pathlength factors as a function of wavelength. Monte Carlo simulations are used in this paper to examine the importance and mitigation methods of this error while the photoelectric pulse wave is detected on the finger tip. We found wavelength selection to be important variables in minimizing such errors, and replacing the average pathlength factor with the subsection pathlength factor appropriately could reduce the error to a small fraction (10%).

BH3-only proteins in tumorigenesis and malignant melanoma

BH3-only proteins are a subset of the Bcl-2 family of apoptotic regulators. BH3-only proteins function as 'damage sensors' in the cell; they are activated in response to cellular stress or DNA damage, whereupon they initiate apoptosis. Apoptosis is the primary mechanism by which the body rids itself of genetically defective cells and is critical for preventing the accumulation of cells with tumorigenic potential. Therefore, dysregulation of BH3-only proteins may promote tumorigenesis. Furthermore, functional apoptosis pathways are required for the success of most cancer treatments, including chemotherapy. Resistance to chemotherapy, as seen with malignant melanoma, often reflects an inability of tumor cells to undergo apoptosis. By deciphering the roles of BH3-only proteins in tumorigenesis, we may learn how to manipulate cell death pathways to overcome apoptotic resistance. This review summarizes the current knowledge of BH3-only proteins and how they contribute to tumorigenesis, with particular attention given to studies involving melanoma.