Stimulation of cyclic GMP efflux in human melanocytes by hypergravity generated by centrifugal acceleration

Gravity alteration (micro- and hypergravity) is known to influence cell functions. As guanosine 3',5'-cyclic monophosphate (cGMP) plays an important role in human melanocyte functions and different guanylyl cyclase isoforms are responsible for cGMP synthesis in human non-metastatic and metastatic melanoma cells, we investigated the effects of hypergravity on the regulation of cGMP levels in cultured human melanocytes and in melanoma cell lines with different metastatic potentials. Hypergravity was produced by horizontal centrifugal acceleration. Here we report that long-term application of hypergravity (up to 5 g for 24 h) stimulated cGMP efflux in cultured melanocytes and in non-metastatic melanoma cells in the presence of 0.1 mM 3-isobutyl-1-methylxanthine (IBMX), a non-selective phosphodiesterase (PDE) inhibitor. Under these conditions, cAMP synthesis and melanin production were up-regulated in pigmented melanocytes and non-metastatic melanoma cells. Hypergravity also stimulated cGMP transport in the presence of 1 microM trequinsin, an inhibitor of cGMP-binding PDE (PDE5) and of transport by multidrug resistance proteins MRP4/5, whereas 50 microM trequinsin partially inhibited cGMP transport. Transport was further inhibited by probenecid, an inhibitor of endogenous non-selective transporters as well as of MRP4/5 and by cycloheximide as an inhibitor of de novo protein synthesis. In contrast, hypergravity did not affect cGMP efflux in metastatic melanoma cells, which might be related to an up-regulated cGMP efflux at 1 g. The results of the present study indicate that hypergravity may stimulate cGMP efflux in melanocytes and in non-metastatic melanoma cells most probably by an enhanced expression of endogenous transporters and/or MRP4/5. Thus, an altered acceleration vector may induce signaling events in melanocytic cells.     

Potential for Cripto-1 in defining stem cell-like characteristics in human malignant melanoma

The diagnosis of melanoma is becoming ever more frequent. Although surgical excision of early lesions is associated with relatively significant high cure rates, treatment modalities are largely unsuccessful for advanced disease. Characteristics such as cellular heterogeneity and plasticity, expression of certain molecules such as the multidrug resistance protein-1 (MDR1) or the aberrant expression of embryonic signaling molecules and morphogens like Nodal, important for self renewal and pluripotency, suggest that a stem cell-like population may reside in aggressive melanomas. This perspective focuses on preliminary findings obtained in our laboratory which indicate that the expression of the Nodal co-receptor, Cripto-1, in a subset of malignant melanoma cells may be exploited to identify possible melanoma stem cells (MSC). In fact, the use of anti-Cripto-1 antibodies to cell sort Cripto-1-positive cells in the metastatic melanoma cell line C8161 has identified a slow growing, sphere forming subpopulation that expresses increased levels of Oct4, Nanog and MDR1. If current in vivo studies confirm the self renewal and tumorigenic characteristics of these cells, the expression of Cripto-1 may represent a useful marker to identify cancer stem cells in melanoma, and possibly other aggressive tumors as well.     

Human interleukin 10 receptor 1/IgG1-Fc fusion proteins: immunoadhesins for human IL-10 with therapeutic potential

Interleukin 10 (IL-10) is produced by various types of human cancer, including malignant melanoma, and plays an important role in negative regulation of cell-mediated immune responses against tumors. We have developed chimeric molecules (immunoadhesins), combining the extracellular domain of human interleukin 10 receptor 1 (IL-10R1) with the Fc regions of human IgG1 heavy chain and investigated their capability of blocking the biological activities of human IL-10. Monomeric and dimeric immunoadhesins (IL-10R1/IgG1) constructs were tested for capturing human IL-10 and blocking its biological activities. Plasmid vectors that contained the IL-10 immunoadhesin constructs were directly transfected into human melanoma cell lines. Transfection of plasmid vectors into melanoma cell lines resulted in capturing of exogenously added as well as endogeneously produced IL-10. The supernatants obtained from an IL-10 non-producing melanoma cell line transfected with monomeric IL-10 immunoadhesin plasmids most efficiently captured exogenously added IL-10, compared to those obtained with the dimeric IL-10R1/IgG1 plasmid vector. Transfection of IL-10-producing melanoma cells with the monomeric IL-10 immunoadhesin plasmids totally captured endogenously produced IL-10 and enhanced T cell responses against allogeneic melanoma cells. Furthermore, purified monomeric IL-10 immunoadhesin protein showed IL-10 capturing efficacy compatible with that of IL-10-specific monoclonal antibodies. Collectively, these studies indicate that IL-10 immunoadhesins, especially in monomeric form, are potent inhibitors of biological activities of IL-10 and suggest that these molecules, alone or in conjunctions with other immunotherapeutic approaches, can be utilized for the immuno-targeting of IL-10 producing tumors. M. Terai and Y. Tamura contributed equally to this work. Yutaka Tamura and Eiko Otsuka are listed as inventors in the pending patent application for IL-10 Immunoadhesins (PCT/JP2004/013090).     

Fractionated irradiation can induce functionally relevant multidrug resistance gene and protein expression in human tumor cell lines

The molecular basis of radiotherapy-related multidrug resistance (MDR) is still unclear. Here we report on a study investigating the effect of fractionated irradiation on expression of the MDR-associated proteins P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP), and lung resistance-related protein (LRP), the respective mRNAs, and the functional consequences. Cells of six colon and five breast cancer cell lines were irradiated with a total dose of 27 Gy, five fractions of 1.8 Gy per week. The mRNA expression was measured by quantitative RT-PCR, protein levels and drug sensitivity to cisplatin, doxorubicin and bendamustine were assessed by flow cytometry. Breast cancer cell lines showed enhancement of the mRNAs encoding for P-gp, MRP1 and LRP in comparison to nonirradiated cells. No up-regulation of the three mRNA species was observed in the colon cancer cell lines. After irradiation, three breast cancer cell lines showed an up-regulation of LRP, one line an up-regulation of MRP1, and four lines a small up-regulation of P-gp. In the colon cancer cell lines, radiation induced significant enhancement of all three proteins. In comparison to controls, the irradiated cells lines showed a significant resistance to cisplatin, doxorubicin and bendamustine. This study confirms the prior reports of enhancement of P-gp and MRP1 after irradiation, which is accompanied by a multidrug resistance phenomenon, but in addition proposes a novel mechanism in the appearance of MDR after radiation-induced enhancement of LRP.     

Epigenetic reprogramming as a key contributor to melanocyte malignant transformation

Melanoma progression requires deregulation of gene expression by currently uncharacterized epigenetic mechanisms. A mouse model based on changes in cell microenvironment was developed by our group to study melanocyte malignant transformation. Melanoma cell lines (4C11- and 4C11+) were obtained as result of 5 sequential anchorage blockades of non-tumorigenic melan-a melanocytes. Melan-a cells submitted to 4 de-adhesion cycles were also established (4C), are non-tumorigenic and represent an intermediary phase of tumor progression. The aim of this work was to identify factors contributing to epigenetic modifications in early and later phases of malignant transformation induced by anchorage impediment. Epigenetic alterations occur early in tumorigenesis; 4C cell line shows changes in global and gene-specific DNA methylation and histone marks. Many histone modifications differ between melan-a, 4C, 4C11- (non-metastatic melanoma cell line) and 4C11+ (metastatic melanoma cell line) which could be associated with changes in gene and microRNA expression. These epigenetic alterations seem to play a key role in malignant transformation since melanocytes treated with 5-Aza-2'-deoxycytidine before each anchorage blockade do not transform. Some epigenetic changes seem to be also responsible for the maintenance of malignant phenotype, since melanoma cell lines (4C11- and 4C11+) treated in vitro with 5-Aza-2'-deoxycytidine or Trichostatin A showed reduction of tumor growth in vivo. Changes in gene expression reflecting cell adaptation to new environment were also observed. We propose a model in which sustained microenvironmental stress in melanocytes results in epigenetic reprogramming. Thus, after adaptation, cells may acquire epigenetic marks that could contribute to the establishment of a malignant phenotype.     

Identification of DNA repair gene Ercc1 as a novel target in melanoma

Increased expression of DNA repair genes contributes to the extreme resistance shown by melanoma to conventional DNA-damaging chemotherapeutics. One such chemotherapeutic effective against a range of other cancers, but not melanoma, is cisplatin. The DNA repair protein, ERCC1, is needed to remove cisplatin-induced DNA damage. We have shown that ERCC1 is essential for melanoma growth and resistance to cisplatin in a mouse xenograft model. Untreated xenografts of our transformed Ercc1-proficient melanocyte cell line grew very rapidly as malignant melanoma. Cisplatin treatment caused initial shrinkage of xenografts, but cisplatin-resistant regrowth soon followed. Cells reisolated into culture had twofold elevated levels of ERCC1 compared to both input cells and cells reisolated from untreated xenografts. An isogenic Ercc1-deficient derivative grew equally well in vitro as the Ercc1-proficient melanocyte cell line. However, in xenografts, the Ercc1-deficient melanomas were much slower to establish and were completely cured by just two cisplatin treatments.     

Establishment and characterization of a non-T, non-B cell lymphoma cell line with T cell receptor beta- and gamma-chain gene rearrangement and possessing MRK 20 monoclonal antibody-defined 85KD protein

A new non-T cell, non-B cell lymphoma cell line, designated IN-1, was established from the ascitic fluid of a patient with non-Hodgkin lymphoma. The IN -1 cells did not show any T cell and B cell immunophenotypes. There were rearrangements of T cell receptor beta- and gamma-chain gene, but no rearrangement of T cell receptor delta-chain gene and immunoglobulin JH gene. Electron microscopically, the cell had numerous pseudopods, mitochondria, vesicles, a conspicuous nucleolus, and scattered heterochromatin at the periphery of the nucleus. They reacted with only OKT9 monoclonal antibody. Molecular analysis revealed that cellular DNA from the IN-1 cells did not hybridize with Bam HI W fragment of EB virus DNA. Cytogenetic analysis showed that the chromosome number of the IN-1 was in the range of 61 -63 whose karyotype analysis demonstrated multiple numerical and structural chromosome changes. The IN-1 cells were resistant to etoposide in comparison with an IC50 of K562 (human chronic myelogenous leukemia). Interestingly, this IN-1 cell possessed 85 KD protein, but not P-glycoprotein, both of which are considered to be multidrug resistance-related proteins.     

CD66a interactions between human melanoma and NK cells: a novel class I MHC-independent inhibitory mechanism of cytotoxicity

NK cells are able to kill virus-infected and tumor cells via a panel of lysis receptors. Cells expressing class I MHC proteins are protected from lysis primarily due to the interactions of several families of NK receptors with both classical and nonclassical class I MHC proteins. In this study we show that a class I MHC-deficient melanoma cell line (1106mel) is stained with several Ig-fused lysis receptors, suggesting the expression of the appropriate lysis ligands. Surprisingly, however, this melanoma line was not killed by CD16-negative NK clones. The lack of killing is shown to be the result of homotypic CD66a interactions between the melanoma line and the NK cells. Furthermore, 721.221 cells expressing the CD66a protein were protected from lysis by YTS cells and by NK cells expressing the CD66a protein. Redirected lysis experiments demonstrated that the strength of the inhibitory effect is correlated with the levels of CD66a expression. Finally, the expression of CD66a protein was observed on NK cells derived from patients with malignant melanoma. These findings suggest the existence of a novel class I MHC-independent inhibitory mechanism of human NK cell cytotoxicity. This may be a mechanism that is used by some of the class I MHC-negative melanoma cells to evade attack by CD66a-positive NK cells.     

Induction of HLA-G expression in a melanoma cell line OCM-1A following the treatment with 5-aza-2＇-deoxycytidine

The non-classical HLA class Ⅰ antigen HLA-G is an immune modulator which inhibits the functions of T cells, NK cells, and the Dendritic cells （DC）. As a result, HLA-G expression in malignant cells may provide them with a mechanism to escape the immune surveillance. In melanoma, HLA-G antigen expression has been found in 30% of surgically removed lesions but in less than 1% of established cell lines. One possible mechanism underlying the differential HLA-G expression in vivo and in vitro is that the HLA-G gene is epigenetically repressed in melanoma cells in vitro. To test this hypothesis, we treated the HLA-G negative melanoma cell line OCM-1A with the DNA methyltransferase inhibitor 5-aza-2＇-deoxycytidine （5-AC） and analyzed whether HLA-G expression can be restored. Our data strongly suggest that HLA-G is silenced as a result of CpG hypermethylation within a 5＇ regulatory region encompassing 220 bp upstream of the start codon. After treatment, HLA-G mRNA expression was dramatically increased. Western blot and flow cytometry showed that HLA-G protein was induced. Interestingly, HLA-G cell surface expression on the 5-AC treated OCM-1A cells is much less than that on the HLA-G positive JEG-3 cells while a similar amount of total HLA-G was observed. Possible mechanisms for the difference were analyzed in the study such as cell cold-treatment, peptide loading and antigen processing machinery components （APM） as well as β2 microglobulin （β2-m） expression. Data revealed that the APM component calreticulin might be involved in the lower HLA-G surface expression on OCM-1A cells. Taken together, our results indicated that DNA methylation is an important epigenetic mechanism by which HLA-G antigen expression is modulated in melanoma cells in vitro. Furthermore, to the first time, we hypothesized that the deficiency of calreticulin might be involved in the low HLA-G surface expression on the 5-AC treated OCM-1A cells.     

Cytotoxic activity of halogenated monoterpenes from Plocamium cartilagineum

Nine halogenated monoterpenes isolated from the red alga Plocamium cartilagineum have been evaluated for their cytotoxic effects on the tumor cell lines CT26 (murine colon adenocarcinoma), SW480 (human colon adenocarcinoma), HeLa (human cervical adenocarcinoma) and SkMel28 (human malignant melanoma) with several multidrug resistance mechanisms and the mammalian non-tumor cell line CHO (Chinese hamster ovary cells). The activities of these compounds were compared with those of the insecticide gamma-hexachlorocyclohexane (lindane) due to chemical structure similarities. Compounds 1, 2, 3, and 5 exhibited selective cytotoxicity against colon and cervical adenocarcinoma cells. Interestingly, the effect of compound 3 was specific and irreversible to human colon adenocarcinoma SW480 cells, which overexpress the transmembrane P-glycoprotein often related to chemoresistance. None of the anti-tumor doses of these compounds was cytotoxic against CHO cells. Furthermore, analysis of cellular extracts after incubation with the test compounds and rotenone (positive uptake control) demonstrated the intracellular accumulation of 1, 2, 3, and 5.     

Cloning and in vitro expression of a melanoma-associated antigen immunogenic in patients with melanoma

The purpose of this study was to identify human melanoma-associated Ag (MAA) that are immunogenic in patients, because these molecules may be useful immunogens to implement active specific immunotherapy. To this end, an expression cDNA library constructed from the human melanoma cell line A375 was screened with sera from patients with melanoma. A 1029-bp cDNA (designated D-1) was isolated. Its nucleotide sequence showed no significant homology with viral and mammalian sequences stored in GE-NETYX. cDNA D-1 hybridized to a 2.0-kb mRNA species from human melanoma, neuroblastoma, erythroleukemia, B lymphoid, and T lymphoid cell lines but not from a renal carcinoma cell line, PBL, and cultured skin fibroblasts. The D-1 clone produced a fusion protein that displayed a significantly higher reactivity with sera from patients with melanoma than from healthy controls. Furthermore, D-1 fusion protein induced in mice antibodies that immunoprecipitated a 50-kDa component from cultured human melanoma cells. The structural properties of D-1 MAA are different from those of previously described MAA. These results suggest that the approach we have applied may be useful to identify novel MAA expressed by melanoma cells. Furthermore, the immunogenicity of recombinant D-1 protein suggests that it may be a valuable immunogen to implement active specific immunotherapy in patients with melanoma, if additional experiments show that it has the appropriate tissue distribution.     

Epigenetic reprogramming as a key contributor to melanocyte malignant transformation

Melanoma progression requires deregulation of gene expression by currently uncharacterized epigenetic mechanisms. A mouse model based on changes in cell microenvironment was developed by our group to study melanocyte malignant transformation. Melanoma cell lines (4C11− and 4C11+) were obtained as result of 5 sequential anchorage blockades of non-tumorigenic melan-a melanocytes. Melan-a cells submitted to 4 de-adhesion cycles were also established (4C), are non-tumorigenic and represent an intermediary phase of tumor progression. The aim of this work was to identify factors contributing to epigenetic modifications in early and later phases of malignant transformation induced by anchorage impediment. Epigenetic alterations occur early in tumorigenesis; 4C cell line shows changes in global and gene-specific DNA methylation and histone marks. Many histone modifications differ between melan-a, 4C, 4C11− (non-metastatic melanoma cell line) and 4C11+ (metastatic melanoma cell line) which could be associated with changes in gene and microRNA expression. These epigenetic alterations seem to play a key role in malignant transformation since melanocytes treated with 5-Aza-2′-deoxycytidine before each anchorage blockade do not transform. Some epigenetic changes seem to be also responsible for the maintenance of malignant phenotype, since melanoma cell lines (4C11− and 4C11+) treated in vitro with 5-Aza-2′-deoxycytidine or Trichostatin A showed reduction of tumor growth in vivo. Changes in gene expression reflecting cell adaptation to new environment were also observed. We propose a model in which sustained microenvironmental stress in melanocytes results in epigenetic reprogramming. Thus, after adaptation, cells may acquire epigenetic marks that could contribute to the establishment of a malignant phenotype.Key words: anchorage blockade, sustained stress, pluripotency, epigenetic reprogramming, malignant melanoma     

The Expression of Tyrosinase,Tyrosinase-Related Proteins 1 and 2 (TRP1 and TRP2), the Silver Protein,and a Melanogenic Inhibitor in Human Melanoma Cells of Differing Melanogenic Activities

The expression of various melanogenic proteins, including tyrosinase, the tyrosinase-related proteins 1 (TRP1) and 2 (TRP2/DOPAchrome tautomerase), and the silver protein in human melanocytes was studied in six different human melanoma cell lines and compared to a mouse derived melanoma cell line. Analysis of the expression of tyrosinase, TRP1, TRP2, and the silver protein using flow cytometry revealed that in general there was a positive correlation between melanin formation and the expression of those melanogenic enzymes. Although several of the melanoma cell lines possessed significant activities of TRP2, the levels of DOPAchrome tautomerase in extracts of human cells were relatively low compared to those in murine melanocytes. Melanins derived from melanotic murine JB/MS cells, from melanotic human Ihara cells and HM-IY cells, from sepia melanin, and from C57BL/6 mouse hair were chemically analyzed. JB/MS cells, as well as Ihara cells and HM-TY cells, possessed significant amounts of 5,6-dihydroxyindole-2-carboxylic acid (DHICA) derived melanins, this being dependent on the activity of TRP2. Kinetic HPLC assays showed that 5,6-dihydroxyindole (DHI) produced during melanogenesis was metabolized quickly to melanin in pigmented KHm-1/4 cells, whereas DHI was stable in amelanotic human SK-MEL-24 cells. A melanogenic inhibitor that has been purified from SK-MEL-24 cells that suppressed oxidation of DHI in the presence or absence of tyrosinase, but had no effect on DHICA oxidation. The sum of these results suggest that the expression of melanogenic enzymes as well as the activity of a melanogenic inhibitor are critical to the production of melanin synthesis in humans.     

Two distinct cytotoxic T lymphocyte subpopulations in patients with Vogt-Koyanagi-Harada disease that recognize human melanoma cells

The functional properties of cytotoxic lymphocytes from patients with Vogt-Koyanagi-Harada disease ( VKH ) specific for human melanoma cells (P-36 melanoma cell line established from a patient with malignant melanoma) were investigated by using monoclonal antibodies specific for human T cell subsets. Peripheral blood lymphocytes (PBL) from patients with VKH showed significant cytotoxic activity against the P-36 (SK-MEL-28) human melanoma cell line, but not against a human cervical carcinoma of the uterus cell line (HeLa-S3 cell line) or against a mouse melanoma cell line (B-16 cell line) originating from a C57BL/6 strain mouse or against the EL-4 mouse lymphoma cell line from a C57BL/6 mouse. The cytotoxic activity of the patients' PBL against the P-36 melanoma cell line was markedly reduced by pretreatment of the PBL with monoclonal anti-human Leu-1 antibody plus rabbit complement, but it was reduced to much less extent by pretreatment with either monoclonal anti-human Leu-2a or Leu-3a antibody plus rabbit complement. The specific cytotoxic activity of the patients' PBL against the P-36 human melanoma cell line is, therefore, mediated by T cells bearing Leu-1+ Leu-2a+ or Leu-1+ Leu-3a+ antigens. Furthermore, the cytotoxic activity was shown to be blocked not only by anti-Leu-2a antibody specific to human cytotoxic/suppressor T cells but also unexpectedly by anti-Leu-3a antibody which has previously been considered to be specific to human inducer/helper T cells. The results of this study suggest that at least two distinct subpopulations of cytotoxic T cells specific for P-36 human melanoma cells are present in the peripheral blood of VKH patients. These cytotoxic T cells have different surface antigens, Leu-2a and Leu-3a.     

Reversion to a homocysteine-responsive phenotype in a human melanoma cell line is associated with diminished growth potential and increased methionine biosynthesis

Our aim was to determine if the isolation of cells capable of proliferating in methionine-free homocysteine-containing medium, from the human MeWo-LC1 melanoma tumor cell line which is unable to proliferate or survive under such conditions, was associated with altered growth properties. Cells which were able to proliferate in methionine-free homocysteine-containing medium (homocysteine-responsive cells) were obtained from the homocysteine-nonresponsive MeWo-LC1 cell line after 8 months of continuous exposure to methionine-free homocysteine-containing medium. Unlike the parental MeWo-LC1 cell line, these homocysteine-responsive cells were also able to proliferate normally in methionine-free medium containing 5'-deoxy-5'-methylthioadenosine. In vitro growth rate, methionine requirement, and capacity to form colonies on soft agarose of these homocysteine-responsive cells were reduced compared to those of the homocysteine-nonresponsive parental MeWo-LC1 cell line. Unlike MeWo-LC1, these homocysteine-responsive cells were able to synthesize [3H]S-adenosylmethionine from [3H]adenine and homocysteine. The failure of the MeWo-LC1 cell line to proliferate in methionine-free homocysteine-containing medium may be due to a deficiency in the synthesis of methionine from homocysteine and 5-methyltetrahydrofolic acid. These results indicate that acquisition of a homocysteine-responsive phenotype in homocysteine-nonresponsive malignant human tumor cells is associated with a reduction in the autonomous growth potential of such cells.     

Molecular characterization of novel melanoma cell lines

We isolated two novel cell lines from different types of sporadic human malignant melanoma: the hmel1 line was obtained from a melanoma skin metastasis and the hmel9 cell line from a primary superficial spreading melanoma. The karyotype and pigmentation parameters were assessed in these cell lines. Cytogenetic analysis in early stages of culture revealed that both cell lines had chromosome instability and simultaneous growth of heteroploid subpopulations. The molecular analysis of some genes involved in melanoma showed that both cell lines harbor BRAF mutations. The unpigmented hmel1 and the pigmented hmel9 lines were found to express the tyrosinase gene. The tyrosine hydroxylase activity was detectable only in hmel9 cells and practically absent in the hmel1 cell line. This activity was found to be correlated with the relative tyrosinase protein amount in both melanoma cell lines. The biological behaviour in the two melanoma cell lines, derived from two different types of melanoma lesions displaying distinct clinical and histopathological features, confirms the heterogeneous characteristics of sporadic melanoma. Similarities and/or differences between cell lines extracted from different melanoma cases could be useful in the future for diagnostic, prognostic and therapeutic purposes.     

Novel Protein Kinase C-Mediated Control of Orai1 Function in Invasive Melanoma

The incidence of malignant melanoma, a cancer of the melanocyte cell lineage, has nearly doubled in the past 20 years. Wnt5A, a key driver of melanoma invasiveness, induces Ca²⁺ signals. To understand how store-operated calcium entry (SOCE) contributes to Wnt5A-induced malignancy in melanoma models, we examined the expression and function of STIM1 and Orai1 in patient-derived malignant melanoma cells, previously characterized as either highly invasive (metastatic) or noninvasive. Using both fluorescence microscopy and electrophysiological approaches, we show that SOCE is greatly diminished in invasive melanoma compared to its level in noninvasive cell types. However, no loss of expression of any members of the STIM and Orai families was observed in invasive melanoma cells. Moreover, overexpressed wild-type STIM1 and Orai1 failed to restore SOCE in invasive melanoma cells, and we observed no defects in their localization before or after store depletion in any of the invasive cell lines. Importantly, however, we determined that SOCE was restored by inhibition of protein kinase C, a known downstream target of Wnt5A. Furthermore, coexpression of STIM1 with an Orai1 mutant insensitive to protein kinase C-mediated phosphorylation fully restored SOCE in invasive melanoma. These findings reveal a level of control for STIM/Orai function in invasive melanoma not previously reported.     

DFNA5 (ICERE-1) contributes to acquired etoposide resistance in melanoma cells

Resistance to drug treatment is a common observation in malignant melanoma. In order to analyze alterations in mRNA expression profiles associated with drug resistance in melanoma cells we previously established a panel of various drug-resistant cell variants derived from the human melanoma line MeWo and compared the mRNA expression profiles by a differential display technique. By that approach it could be demonstrated that the expression level of a mRNA encoded by a gene found to be mutated in non-syndromic hearing impairment, DFNA5 (ICERE-1), was distinctly decreased in the 33-fold etoposide-resistant melanoma cell line MeWo ETO 1. To evaluate the hypothesis that a decrease in DFNA5 mRNA expression level contributes to the acquired etoposide resistance phenotype exhibited by MeWo ETO 1 cells, this drug-resistant line was stably transfected with the DFNA5-encoding cDNA. Transfected clones showed a 30-35% reduced etoposide susceptibility by comparing the IC(25), IC(50) and IC(75) values of these clones with those displayed by the non-transfected, etoposide-resistant melanoma cell line MeWo ETO 1 and controls. Furthermore, etoposide exposure of stable DFNA5 transfectants resulted in an increase of caspase-3-mediated apoptotic events in DFNA5-transfected clones in comparison to MeWo ETO 1 cells and controls. The data therefore demonstrate that a decrease in DNFA5 mRNA expression level is associated with an increased etoposide resistance in melanoma cells due to an elevated cellular susceptibility to trigger a caspase-3-depending signal pathway leading to programmed cell death.     

Separate roles for the Golgi apparatus and lysosomes in the sequestration of drugs in the multidrug-resistant human leukemic cell line HL-60

The sequestration of drugs away from cellular target sites into cytoplasmic organelles of multidrug-resistant (MDR) cancer cells has been recently shown to be a cause for ineffective drug therapy. This process is poorly understood despite the fact that it has been observed in a large number of MDR cancer cell lines. Analysis of drug sequestration in these cells has traditionally been done using fluorescent anthracycline antibiotics (i.e. daunorubicin, doxorubicin). This narrow selection of substrates has resulted in a limited understanding of sequestration mechanisms and the intracellular compartments that are involved. To better characterize this phenotype, we chose to examine the sequestration of molecules having different acid/base properties in the MDR HL-60 human leukemic cell line. Here we show that weakly basic drug daunorubicin is sequestered into lysosomes according to a pH partitioning type mechanism, whereas sulforhodamime 101, a zwitterionic molecule, is sequestered into the Golgi apparatus through a drug transporter-mediated process. Quantitative intracellular pH measurements reveal that the lysosome-tocytosol pH gradient is expanded in the MDR line. Moreover, the MDR cells overexpress the multidrug resistance-related protein (MRP1), which is localized to the Golgi apparatus. These results demonstrate, for the first time, that two distinct mechanisms for intracellular compartmentalization are operational in a single MDR cell line.