Biomedical subjects

Ruth Halaban

Publications and source records attributed to Ruth Halaban.

15 recordsLinked to original sources

PubMed2006

Rab33A: characterization, expression, and suppression by epigenetic modification.

Rab33A, a member of the small GTPase superfamily, is an X-linked gene that is expressed in brain, lymphocytes, and normal melanocytes, but is downregulated in melanoma cells. We demonstrate that in normal melanocytes Rab33A colocalizes with melanosomal proteins and that a constitutively active GTPase mutant suppresses their transport to the melanosomes. In the brain, Rab33A is present throughout the cortex, as well as in the hippocampal CA fields. A survey of melanocytic lesions demonstrated that aberrant downregulation of Rab33A is an early event that is already prevalent in melanocytes of giant congenital nevi. Analyses of bisulfite-modified DNA revealed that Rab33A is regulated by DNA methylation of a specific promoter region proximal to the transcription initiation site, and that suppression of Rab33A in melanoma cells recapitulates normal processes that control silencing of X-linked genes, but not tissue specific gene expression. This information is important for understanding carcinogenesis as well as other aberrant processes because Rab33A may have an important role in disorders involving X-chromosome-linked genes associated with vesicular transport.

Amino Acid Sequence↗

PubMed2006

Expression of tumor necrosis factor--related apoptosis-inducing ligand receptors 1 and 2 in melanoma.

PURPOSE: The proapoptotic receptors tumor necrosis factor--related apoptosis-inducing ligand receptor 1 (TRAIL-R1) and TRAIL-R2 are targets of drugs in clinical development, and receptor expression levels may be important determinants of sensitivity to receptor agonists. We assessed TRAIL-R1 and TRAIL-R2 expression patterns in a large cohort of melanomas and benign nevi. EXPERIMENTAL DESIGN: We analyzed tissue microarrays containing 546 melanomas and 540 nevi using our automated quantitative method to measure protein levels in situ (AQUA). The system uses S100 to define pixels as melanoma (tumor mask) within the array spot and measures intensity of TRAIL-receptor expression using Cy5-conjugated antibodies within the mask. AQUA scores were correlated with clinical and pathologic variables. RESULTS: TRAIL-R1 and TRAIL-R2 expression was higher in melanomas than in nevi (P < 0.0001), and higher in primary than in metastatic specimens (P = 0.0031 and P < 0.0001, respectively). TRAIL-R1 and TRAIL-R2 expression exceeding the 95th percentile for nevi was found in 19% and 74% of melanoma specimens, respectively. Although on univariate analysis, high TRAIL-R2 expression correlated with increased survival (P = 0.0439), it was not associated with survival within the primary or metastatic subcohorts. TRAIL-R1 expression was not associated with survival. CONCLUSIONS: TRAIL-R1 and TRAIL-R2 expression is higher in malignant melanocytes than in their benign counterparts, suggesting that these receptors might be effective therapeutic targets in melanoma. Expression is higher in early-stage disease than in metastatic specimens, and expression exceeding that found in nevi is found in a substantially larger fraction of melanomas for TRAIL-R2 compared with TRAIL-R1. Assessment of baseline tumor TRAIL receptor expression may be important in analysis of clinical trials involving TRAIL receptor agonists.

Gene Expression Regulation↗

PubMed2005

Rb/E2F: a two-edged sword in the melanocytic system.

Rb is a tumor suppressor that represses the expression of E2F regulated genes required for cell cycle progression. It is inactivated in melanomas and other cancer cells by phosphorylation catalyzed by persistent cyclin dependent kinase (CDK) activity. CDK activity is sustained in melanoma cells mostly by the elimination of the CDK inhibitor p16INK4A and by high levels of cyclins whose expression is maintained by stimuli emanating from activated cell surface receptors and/or mutated intracellular intermediates, such as N-Ras and B-Raf. However, Rb also suppresses the expression of apoptosis genes, and its presence protects normal melanocytes from cell death. Its high expression in human melanoma cells and tumors suggests a similar role in malignant cells as well. The differential release and suppression of E2F transcriptional activity is likely to depend on promoter-specific E2F/Rb interaction. Phosphorylated Rb is displaced from cell cycle genes but not from others. In addition, Rb gene repression is dependent on the nature of Rb-E2F interaction and the activity of the Rb-bound proteins recruited to the promoter. Deciphering the differences in Rb/E2F complex formation in normal and malignant melanocytes is likely to shed light on the mechanism by which Rb can exert tumor suppressing and promoting activities in this cellular system. The Rb/E2F pathway provides opportunities for efficient therapy at multiple levels. Novel drugs can reactivate Rb potential to suppress growth cycle promoting genes. In addition, the high E2F transcriptional activity in melanoma cells can be exploited to deliver cytotoxic molecules specifically to tumors, sparing the normal tissues.

Apoptosis↗

PubMed2005

Melanocyte and keratinocyte carcinogenesis: p53 family protein activities and intersecting mRNA expression profiles.

Melanocytes and keratinocytes were analyzed for potential roles of p53, p73, and p63 tumor suppressor family proteins and of malignancy-specific gene expression changes in the etiology of multi-step cancer. Melanocytes expressed deltaNp73alpha, two p63 isoforms and p53. Although p21 and Noxa mRNA levels increased following DNA damage, p53 family member binding to p21 and Noxa DNA probes was undetectable, suggesting p53 family-independent responses. In contrast, keratinocytes expressed multiple isoforms each of p73 and p63 that were induced to bind p21 and Noxa DNA probes after ionizing (IR) or after ultraviolet B (UVB) irradiation, correlating with p21 and Noxa mRNA induction and with apoptosis. Interestingly, IR-resistant malignant melanocytes and keratinocytes both exhibited Noxa mRNA induction after UVB treatment, correlating with DNA binding of p53 family proteins to the Noxa probe only in keratinocytes. To uncover other malignancy-specific events, we queried mouse initiated keratinocyte clones for early changes that were exacerbated in malignant derivatives and also differentially expressed in human advanced melanoma versus normal melanocytes. Using a new method for ranking and normalization of microarray data for 5000 probe sets, 27 upregulated and 13 downregulated genes satisfied our query. Of these, the majority was associated with late-stage human cancers and six were novel genes. Thus, clonal lineage mouse models representing early through late cancer progression stages may inform the focus on early, potentially causal events from microarray studies of human cancers, facilitating prognosis and molecular therapy.

Animals↗

PubMed2004

Automated quantitative analysis of HDM2 expression in malignant melanoma shows association with early-stage disease and improved outcome.

The incidence of cutaneous malignant melanoma continues to increase every year, and this disease remains the leading cause of skin cancer death in industrialized countries. Despite the aggressive nature of advanced melanoma, there are no standard biological assays in clinical usage that can predict metastasis. This may be due, in part, to the inadequacy of reproducible assessment of protein expression using traditional immunohistochemistry. We have previously described a novel method of quantitative assessment of protein expression (AQUA) with the continuity and accuracy of an ELISA assay but with maintenance of critical spatial information. Here, we modify this technology for the evaluation of protein expression in melanoma. Using a tissue microarray cohort of 405 melanoma lesions and 17 normal skin samples, we analyzed expression of HDM2, the human homologue of murine double minute 2 with automated quantitative analysis. We show that expression levels in the nucleus are significantly higher in primary melanomas than in metastatic lesions. Furthermore, high levels of expression are predictive of better outcome. This study demonstrates that quantitative assessment of protein expression is useful in melanoma to validate potential tissue biomarkers and suggests that human homologue of murine double minute 2 may be a valuable prognostic tool for management of malignant melanoma.

Biomarkers, Tumor↗

PubMed2004

Expression profiling reveals novel pathways in the transformation of melanocytes to melanomas.

Affymetrix and spotted oligonucleotide microarrays were used to assess global differential gene expression comparing normal human melanocytes with six independent melanoma cell strains from advanced lesions. The data, validated at the protein level for selected genes, confirmed the overexpression in melanoma cells relative to normal melanocytes of several genes in the growth factor/receptor family that confer growth advantage and metastasis. In addition, novel pathways and patterns of associated expression in melanoma cells not reported before emerged, including the following: (a) activation of the NOTCH pathway; (b) increased Twist expression and altered expression of additional transcriptional regulators implicated in embryonic development and epidermal/mesenchymal transition; (c) coordinated activation of cancer/testis antigens; (d) coordinated down-regulation of several immune modulation genes, in particular in the IFN pathways; (e) down-regulation of several genes implicated in membrane trafficking events; and (f) down-regulation of growth suppressors, such as the Prader-Willi gene NECDIN, whose function was confirmed by overexpression of ectopic Flag-necdin. Validation of differential expression using melanoma tissue microarrays showed that reduced ubiquitin COOH-terminal esterase L1 in primary melanoma is associated with worse outcome and that increased expression of the basic helix-loop-helix protein Twist is associated with worse outcome. Some differentially expressed genes reside on chromosomal regions displaying common loss or gain in melanomas or are known to be regulated by CpG promoter methylation. These results provide a comprehensive view of changes in advanced melanoma relative to normal melanocytes and reveal new targets that can be used in assessing prognosis, staging, and therapy of melanoma patients.

Animals↗

PubMed2004

Carbohydrates act as sorting determinants in ER-associated degradation of tyrosinase.

The endoplasmic reticulum (ER) quality-control machinery maintains the fidelity of the maturation process by sorting aberrant proteins for ER-associated protein degradation (ERAD), a process requiring retrotranslocation from the ER lumen to the cytosol and degradation by the proteasome. Here, we assessed the role of N-linked glycans in ERAD by monitoring the degradation of wild-type (Tyr) and albino mutant (Tyr(C85S)) tyrosinase. Initially, mutant tyrosinase was established as a genuine ERAD substrate using intact melanocyte and semi-permeabilized cell systems. Inhibiting mannose trimming or accumulating Tyr(C85S) in a monoglucosylated form led to its stabilization, supporting a role for lectin chaperones in ER retention and proteasomal degradation. In contrast, ablating the lectin chaperone interactions by preventing glucose trimming caused a rapid disappearance of tyrosinase, initially due to the formation of protein aggregates, which were subsequently degraded by the proteasome. The co-localization of aggregated tyrosinase with protein disulfide isomerase and BiP, but not calnexin, supports an ER organization, which aids in protein maturation and degradation. Based on these studies, we propose a model of tyrosinase degradation in which interactions between N-linked glycans and lectin chaperones help to minimize tyrosinase aggregation and also target non-native substrates for retro-translocation and subsequent degradation.

Adenosine Triphosphate↗

PubMed2004

Novel tyramide-based tyrosinase assay for the detection of melanoma cells in cytological preparations.

Fine-needle aspiration (FNA) has been used as a fast, minimally invasive, and reliable method for the evaluation of enlarged lymph nodes. However, there are some cases where the definitive diagnosis cannot be elicited with morphology alone, especially cases without a known primary lesion. Although immunocytochemical studies may be helpful in some situations, they are often complicated by nonspecific staining. Recently, a novel tyramide-based tyrosinase assay was developed. Since melanocytes, both benign and malignant, produce tyrosinase, we postulated that this assay could be useful as an in situ biochemical diagnostic test. We modified the Perkin Elmer TSA assay, a commercial assay based on tyramide, a tyrosine analog that is a substrate for tyrosinase, for use on air-dried cytological preparations. We validated the assay on cell lines, then tested a small series of melanoma and nonmelanoma cytology specimens. The YUGEN8 melanoma cell line was used to optimize the assay and it showed abundant reaction product, while HeLa cells served as a negative control. All melanoma cytology specimens were positive and all nonmelanoma specimens were negative. These results suggest that this simple, fast, and inexpensive assay is a sensitive and specific method for detection of melanoma cells in cytology specimens. This method may be a useful ancillary procedure for the resolution of challenging melanoma cases.

Biopsy, Fine-Needle↗

PubMed2004

Her2/neu is not a commonly expressed therapeutic target in melanoma -- a large cohort tissue microarray study.

Melanoma is among the most chemotherapy-resistant malignancies. Numerous new agents have been developed that target specific molecules on cancer cells, including the monoclonal antibody trastuzumab, which targets Her2/neu and has been very beneficial in the treatment of breast cancer. There are conflicting reports in the literature about Her2/neu expression in melanoma specimens, but all of the cohorts studied have been small. We therefore examined Her2/neu expression in a very large cohort of melanoma specimens in order to determine the value of exploring trastuzumab therapy for melanoma patients. Immunohistochemical staining was performed on two tissue microarrays, together containing 600 intact specimens. Expression was evaluated semi-quantitatively and correlated with tumour stage and other clinicopathological data. Of the 600 specimens in the cohort, 31 patients (5.2%) had positive Her2/neu expression. Among the primary cutaneous specimens (n=269), 7% had positive Her2/neu staining, while 3.6% of the recurrent or metastatic specimens (n=331) had positive Her2/neu staining (P=0.06). Among the primary lesions there was no significant correlation between Her2/neu expression, Clark level and ulceration; however, Her2/neu expression was associated with lesions with a Breslow depth of < 2 mm (P=0.05). Using this very large cohort of melanoma specimens, we found only a few cases with aberrant Her2/neu expression, many of them being primary cutaneous lesions rather than recurrent or metastatic lesions. Our findings suggest that drugs that specifically target Her2/neu are not likely to be useful for the treatment of metastatic melanoma or as adjuvant therapy for melanoma patients at high risk for recurrence.

Cohort Studies↗

PubMed2003

Subcellular localization of activating transcription factor 2 in melanoma specimens predicts patient survival.

The transcription factor activating transcription factor 2 (ATF2) has been shown to be associated with melanocytic oncogenesis and melanoma tumor proliferation in preclinical models. The clinical significance of ATF2 expression is unknown. To determine the prognostic value of ATF2 in melanoma, we evaluated the pattern and level of ATF2 expression in a large cohort of melanoma specimens. Immunohistochemical staining was performed on a tissue microarray representing 544 patients with a mean follow-up time of 60 months. Expression was evaluated semiquantitatively and correlated with overall survival and other clinicopathological data. Strong cytoplasmic ATF2 expression was associated with primary specimens rather than metastases (P < 0.0001) and with better survival (P = 0.0003). Strong nuclear ATF2 expression was associated with metastatic specimens (P < 0.0001) and with poor survival (P = 0.0008). Patients who had both weak cytoplasmic and strong nuclear ATF2 staining had the worst outcome, both among the full cohort of patients (P < 0.0001) and among the patients with localized disease (n = 269; P < 0.0001). On multivariate analysis of the primary cutaneous specimens, weak cytoplasmic staining and strong nuclear staining was an independent predictor of poor outcome, as was Clark level. Nuclear ATF2 is likely to be transcriptionally active, whereas cytoplasmic ATF2 probably represents an inactive form. These findings support other preclinical findings in which transcriptionally active ATF2 is involved in tumor progression-proliferation in melanoma. Moreover, our findings suggest that ATF2 might be a useful prognostic marker in early-stage melanoma.

Activating Transcription Factor 2↗

PubMed2003

Tyrosinase maturation and oligomerization in the endoplasmic reticulum require a melanocyte-specific factor.

Tyrosinase is a glycoprotein responsible for the synthesis of melanin in melanocytes. A large number of mutations have been identified in tyrosinase, with many leading to its misfolding, endoplasmic reticulum (ER) retention, and degradation. Here we describe the folding and maturation of human tyrosinase (TYR) using an in vitro translation system coupled with ER-derived microsomes or with semipermeabilized cells, as an intact ER source. TYR remained misfolded as determined by its sensitivity to trypsin digestion and its persistent interaction with the ER resident lectin chaperones calnexin and calreticulin when produced in ER-derived microsomes or nonmelanocytic semipermeabilized cells. However, when TYR was translocated into semipermeabilized melanocytes, chaperone interactions were transient, maturation progressed to a trypsin-resistant state, and a TYR homodimer was formed. The use of semipermeabilized mouse melanocytes defective for tyrosinase or other melanocyte-specific proteins as the ER source indicated that proper TYR maturation and oligomerization were greatly aided by the presence of wild type tyrosinase and tyrosinase-related protein 1. These findings suggested that oligomerization is a step in proper TYR maturation within the ER that requires melanocyte-specific factors.

Animals↗

PubMed2003

The tyrphostin AG1024 accelerates the degradation of phosphorylated forms of retinoblastoma protein (pRb) and restores pRb tumor suppressive function in melanoma cells.

Constitutive cell surface receptor kinase signaling and persistent phosphorylation/inactivation of the retinoblastoma (pRb) family of proteins (pRb, p107 and p130, known as pocket proteins) have been implicated in conferring uncontrolled growth to melanoma cells. However, the signals linking receptor kinase activity to neutralization of pocket proteins have not yet been fully elucidated. We therefore used specific chemical inhibitors to examine pRb regulation in melanoma cells. The most efficient agent, AG1024, known as an inhibitor of insulin-like growth factor 1 receptor and insulin receptor, arrested melanoma cell growth in vitro at nanomolar concentrations within 24 h of application. AG1024 inhibited the mitogen-activated protein kinase/extracellular signal-regulated kinase pathway and restored pRb tumor suppressive function. The latter was observed by the reduction in the phosphorylated forms of pRb, p107 and p130, and the formation of growth suppressive DNA binding complexes consisting of pRb and E2F1 or E2F3. The loss of phosphorylated forms of pRb at early time points after AG1024 application was not associated with suppression of cyclin-dependent kinases 2 and 4 activity but rather with proteasomal and nonproteasomal degradation. Thus, inhibition of melanoma cell proliferation by AG1024 is mediated by inhibition of mitogen-activated protein kinase/extracellular signal-regulated kinase 2 signaling and activation of pRb by a mechanism involving protein degradation.

Animals↗

PubMed2002

Abnormal acidification of melanoma cells induces tyrosinase retention in the early secretory pathway.

In tyrosinase-positive amelanotic melanoma cells, inactive tyrosinase accumulates in the endoplasmic reticulum. Based on studies described here, we propose that aberrant vacuolar proton ATPase (V-ATPase)-mediated proton transport in melanoma cells disrupts tyrosinase trafficking through the secretory pathway. Amelanotic but not melanotic melanoma cells or normal melanocytes display elevated proton export as observed by the acidification of the extracellular medium and their ability to maintain neutral intracellular pH. Tyrosinase activity and transit through the Golgi were restored by either maintaining the melanoma cells in alkaline medium (pH 7.4-7.7) or by restricting glucose uptake. The translocation of tyrosinase out of the endoplasmic reticulum and the induction of cell pigmentation in the presence of the ionophore monensin or the specific V-ATPase inhibitors concanamycin A and bafilomycin A1 supported a role for V-ATPases in this process. Because it was previously shown that V-ATPase activity is increased in solid tumors in response to an acidified environment, the appearance of hypopigmented cells in tyrosinase-positive melanoma tumors may indicate the onset of enhanced glycolysis and extracellular acidification, conditions known to favor metastatic spread and resistance to weak base chemotherapeutic drugs.

Acids↗

PubMed2002

Coexpression of wild-type tyrosinase enhances maturation of temperature-sensitive tyrosinase mutants.

Tyrosinase is a type I membrane glycoprotein whose activity is essential for melanin synthesis. Loss of function mutations in tyrosinase is the cause of oculocutaneous albinism 1. In the milder oculocutaneous albinism 1B form in which mutant proteins retain residual activity, the severity of albinism depends on the type of mutations expressed in the melanocyte. In this study, we show that coexpression of wild-type protein with temperature-sensitive tyrosinase mutants corrects the mutant conformation defect in an activity-dependent manner. Exit from the endoplasmic reticulum and complex carbohydrate processing in the Golgi was promoted when temperature-sensitive tyrosinase mutants were ectopically expressed in host melanocytes carrying wild-type protein even at the nonpermissive temperature. Incubation of transfected melanocytes with DOPA (the cofactor and substrate for tyrosinase), or tyrosine (the substrate), further enhanced processing of ectopic mutant proteins. The analysis of glycosylation-deficient mutants revealed regions in tyrosinase with high, low, and intermediate dependency on glycans for maturation. We concluded that the presence of tyrosinase activity enhances the maturation of temperature-sensitive and glycosylation-deficient forms of tyrosinase. The results may explain the variation in pigmentation and the development of pigment later in life in patients carrying different mutant alleles of oculocutaneous albinism 1B.

Albinism, Oculocutaneous↗

PubMed2002

Pigmentation in melanomas: changes manifesting underlying oncogenic and metabolic activities.

Changes in pigmentation are frequently encountered in primary and metastatic melanocytic lesions. Pigmentation is determined by the activity of tyrosinase (TYR), the rate-limiting enzyme in melanin synthesis. Tyrosinase activity can be modulated at the genetic and/or epigenetic level. In this commentary I suggest that pigmentation can serve as an indicator for genetic and metabolic changes as follows. In TYR-negative, amelanotic melanomas cells, downregulation of TYR and other melanocyte-specific gene expression is likely to be mediated by dominantly acting oncogenes with impact on the transcriptional activity of the melanocyte-specific transcription factor Mitf. Ras and c-myc, shown to be active and upregulated in subclasses of melanoma tumors, have the potential to induce these changes. TYR-positive highly pigmented melanoma tumors are likely to reside in aerobic, well-vascularized microenvironment. In contrast, hypo- or amelanotic TYR-positive lesions suffer from reduced TYR activity due to an acidified microenvironment. These lesions might have encountered anaerobic conditions, and have adapted to the reduced oxygen by enhanced glycolysis, leading to extracellular acidification and activation of V-ATPase.

Gene Expression Regulation, Neoplastic↗