Fabiana Henriques Machado de Melo

Timp1 interacts with beta-1 integrin and CD63 along melanoma genesis and confers anoikis resistance by activating PI3-K signaling pathway independently of Akt phosphorylation

BackgroundAnoikis resistance is one of the abilities acquired along tumor progression. This characteristic is associated with metastasis development, since tumorigenic cells must survive independently of cell-matrix interactions in this process. In our laboratory, it was developed a murine melanocyte malignant transformation model associated with a sustained stressful condition. After subjecting melan-a melanocytes to 1, 2, 3 and 4 cycles of anchorage impediment, anoikis resistant cells were established and named 1C, 2C, 3C and 4C, respectively. These cells showed altered morphology and PMA independent cell growth, but were not tumorigenic, corresponding to pre-malignant cells. After limiting dilution of 4C pre-malignant cells, melanoma cell lines with different characteristics were obtained. Previous data from our group showed that increased Timp1 expression correlated with anoikis-resistant phenotype. Timp1 was shown to confer anchorage-independent growth capability to melan-a melanocytes and render melanoma cells more aggressive when injected into mice. However, the mechanisms involved in anoikis regulation by Timp1 in tumorigenic cells are not clear yet.MethodsThe β1-integrin and Timp1 expression were evaluated by Western blotting and CD63 protein expression by flow cytometry using specific antibodies. To analyze the interaction among Timp1, CD63 and β1-integrin, immunoprecipitation assays were performed, anoikis resistance capability was evaluated in the presence or not of the PI3-K inhibitors, Wortmannin and LY294002. Relative expression of TIMP1 and CD63 in human metastatic melanoma cells was analyzed by real time PCR.ResultsDifferential association among Timp1, CD63 and β1-integrins was observed in melan-a melanocytes, 4C pre-malignant melanocytes and 4C11- and 4C11+ melanoma cells. Timp1 present in conditioned medium of melanoma cells rendered melan-a melanocytes anoikis-resistant through PI3-K signaling pathway independently of Akt activation. In human melanoma cell lines, in which TIMP1 and beta-1 integrin were also found to be interacting, TIMP1 and CD63 levels together was shown to correlate significantly with colony formation capacity.ConclusionsOur results show that Timp1 is assembled in a supramolecular complex containing CD63 and β1-integrins along melanoma genesis and confers anoikis resistance by activating PI3-K signaling pathway, independently of Akt phosphorylation. In addition, our data point TIMP1, mainly together with CD63, as a potential biomarker of melanoma.

Enhanced OXPHOS, glutaminolysis and β-oxidation constitute the metastatic phenotype of melanoma cells

Tumours display different cell populations with distinct metabolic phenotypes. Thus, subpopulations can adjust to different environments, particularly with regard to oxygen and nutrient availability. Our results indicate that progression to metastasis requires mitochondrial function. Our research, centered on cell lines that display increasing degrees of malignancy, focused on metabolic events, especially those involving mitochondria, which could reveal which stages are mechanistically associated with metastasis. Melanocytes were subjected to several cycles of adhesion impairment, producing stable cell lines exhibiting phenotypes representing a progression from non-tumorigenic to metastatic cells. Metastatic cells (4C11+) released the highest amounts of lactate, part of which was derived from glutamine catabolism. The 4C11+ cells also displayed an increased oxidative metabolism, accompanied by enhanced rates of oxygen consumption coupled to ATP synthesis. Enhanced mitochondrial function could not be explained by an increase in mitochondrial content or mitochondrial biogenesis. Furthermore, 4C11+ cells had a higher ATP content, and increased succinate oxidation (complex II activity) and fatty acid oxidation. In addition, 4C11+ cells exhibited a 2-fold increase in mitochondrial membrane potential (ΔΨmit). Consistently, functional assays showed that the migration of cells depended on glutaminase activity. Metabolomic analysis revealed that 4C11+ cells could be grouped as a subpopulation with a profile that was quite distinct from the other cells investigated in the present study. The results presented here have centred on how the multiple metabolic inputs of tumour cells may converge to compose the so-called metastatic phenotype.

Chounergic modulation of inhibitory avoidance impairment induced by paradoxical sleep deprivation

1. Male Wistar rats were submitted to paradoxical sleep deprivation for 96 hr by a modified multiple platform technique. 2. Training of step-through inhibitory avoidance was performed immediately after the last day of paradoxical sleep deprivation. Twenty-four hr after training the animals were submitted to the retention test. 3. In Experiment 1, pilocarpine (4 mg/kg, i.p.) or atropine (4 mg/kg, i.p.) were administered daily during the paradoxical sleep deprivation period. Pilocarpine, but not atropine, reversed the impairment induced by PS deprivation. 4. In Experiment 2, pilocarpine (4, 8 and 12 mg/kg, i.p.) was injected 1 hr before training in order to verify if the reversal of memory impairment was an effect secondary to residual enhanced blood levels of pilocarpine during training. Acute treatment with pilocarpine, in any dose, did not reverse the impairment produced by paradoxical sleep deprivation 5. Activation of the cholinergic system during the period of deprivation is able to prevent memory deficits induced by paradoxical sleep deprivation.

Ras and Rac1, Frequently Mutated in Melanomas, Are Activated by Superoxide Anion, Modulate Dnmt1 Level and Are Causally Related to Melanocyte Malignant Transformation

A melanocyte malignant transformation model was developed in our laboratory, in which different melanoma cell lines were obtained after submitting the non-tumorigenic melanocyte lineage melan-a to sequential cycles of anchorage impediment. Our group has already showed that increased superoxide level leads to global DNA hypermemethylation as well increased Dnmt1 expression few hours after melanocyte anchorage blockade. Here, we showed that Ras/Rac1/ERK signaling pathway is activated in melanocytes submitted to anchorage impediment, regulating superoxide levels, global DNA methylation, and Dnmt1 expression. Interestingly, Ras and Rac1 activation is not related to codon mutations, but instead regulated by superoxide. Moreover, the malignant transformation was drastically compromised when melan-a melanocytes were submitted to sequential cycles of anchorage blockage in the presence of a superoxide scavenger. This aberrant signaling pathway associated with a sustained stressful condition, which might be similar to conditions such as UV radiation and inflammation, seems to be an early step in malignant transformation and to contribute to an epigenetic reprogramming and the melanoma development.

Endothelial nitric oxide synthase uncoupling as a key mediator of melanocyte malignant transformation associated with sustained stress conditions

Melanoma cell lines and cells corresponding to premalignant melanocytes were established by our group after subjecting a nontumorigenic murine melanocyte lineage, melan-a, to sequential cycles of anchorage blockade. Previous results showed that in melan-a cells the superoxide level increases after such procedure. Superoxide production during melanocyte de-adhesion was inhibited by L-sepiapterin, the precursor of eNOS cofactor BH4, and increased by the inhibitor of BH4 synthesis, DAHP, hence indicating a partial uncoupling state of eNOS. The eNOS uncoupling seems to be maintained in cells derived from melan-a, because they present decreased nitric oxide and increased superoxide levels. The inhibition of superoxide production in Tm5 melanoma cells with L-sepiapterin reinforces their eNOS-uncoupled state. The maintenance of oxidative stress seems to be important in melanoma apoptosis resistance because Mn(III)TBAP, a superoxide scavenger, or L-sepiapterin renders Tm5 cells more sensitive to anoikis and chemotherapy. More importantly, eNOS uncoupling seems to play a pivotal role in melanocyte malignant transformation induced by sustained anchorage impediment, because no malignant transformation was observed when L-NAME-treated melanocytes were subjected to sequential cycles of de-adhesion. Our results show that uncoupled eNOS contributes to superoxide production during melanocyte anchorage impediment, contributing to anoikis resistance and malignant transformation.

Receptor tyrosine kinases and downstream pathways as druggable targets for cancer treatment: the current arsenal of inhibitors

Searching for targets that allow pharmacological inhibition of cell proliferation in over-proliferative states, such as cancer, leads us to finely understand the complex mechanisms orchestrating the perfect control of mitosis number, frequency and pace as well as the molecular arrangements that induce cells to enter functional quiescence and brings them back to cycling in specific conditions. Although the mechanisms regulating cell proliferation have been described several years ago, never before has so much light been shed over this machinery as during the last decade when therapy targets have been explored and molecules, either synthetic or in the form of antibodies with the potential of becoming cancer drugs were produced and adjusted for specific binding and function. Proteins containing tyrosine kinase domains, either membrane receptors or cytoplasmic molecules, plus the ones activated by those in downstream pathways, having tyrosine kinase domains or not, such as RAS which is a GTPase and serine/threonine kinases such as RAF, play crucial role in conducting proliferation information from cell surroundings to the nucleus where gene expression takes place. Tyrosine kinases phosphorylate tyrosine residues in an activating mode and are found in important growth factor receptors, such as for ligands from families collectively known as VEGF, PDGF and EGF, to name a few and in intracellular downstream molecules. They all play important roles in normal physiology and are commonly found mutated or overexpressed in neoplastic states. Our objective here is to present such kinases as druggable targets for cancer therapy, highlighting the ones for which the pharmacological arsenal is available, discussing specificity, resistance mechanisms and treatment alternatives in cases of resistance, plus listing potential targets that have not been successfully worked yet.

The Role of Oxidative Stress in Melanoma Development, Progression and Treatment

Oxygen free radicals or, more generally, reactive oxygen species (ROS) are products of normal cellular metabolism. They are well recognized for playing a contradictory dual role in living systems, sometimes deleterious sometimes beneficial, depending on cell type, genetic back‐ ground and levels and types of species involved. Beneficial effects of ROS occur at low/ moderate concentrations and involve modulation of signaling pathways and gene expression regulation. The harmful effect of free radicals is termed oxidative stress and can result in damage to cellular lipids, proteins and DNA. The balance between benign and deleterious effects of ROS is a decisive factor of living organisms and is controlled by mechanisms called redox regulation. This process protects cells from oxidative stress and maintains the redox homeostasis by modulating the redox state in vivo [17].

Timp1 Promotes Cell Survival by Activating the PDK1 Signaling Pathway in Melanoma

High TIMP1 expression is associated with poor prognosis in melanoma, where it can bind to CD63 and β1 integrin, inducing PI3-kinase pathway and cell survival. Phosphatidylinositol (3,4,5)-trisphosphate (PIP3), generated under phosphatidylinositol-3-kinase (PI3K) activation, enables the recruitment and activation of protein kinase B (PKB/AKT) and phosphoinositide-dependent kinase 1 (PDK1) at the membrane, resulting in the phosphorylation of a host of other proteins. Using a melanoma progression model, we evaluated the impact of Timp1 and AKT silencing, as well as PI3K, PDK1, and protein kinase C (PKC) inhibitors on aggressiveness characteristics. Timp1 downregulation resulted in decreased anoikis resistance, clonogenicity, dacarbazine resistance, and in vivo tumor growth and lung colonization. In metastatic cells, pAKTThr308 is highly expressed, contributing to anoikis resistance. We showed that PDK1Ser241 and PKCβIISer660 are activated by Timp1 in different stages of melanoma progression, contributing to colony formation and anoikis resistance. Moreover, simultaneous inhibition of Timp1 and AKT in metastatic cells resulted in more effective anoikis inhibition. Our findings demonstrate that Timp1 promotes cell survival with the participation of PDK1 and PKC in melanoma. In addition, Timp1 and AKT act synergistically to confer anoikis resistance in advanced tumor stages. This study brings new insights about the mechanisms by which Timp1 promotes cell survival in melanoma, and points to novel perspectives for therapeutic approaches.

Heparan sulfate proteoglycan deficiency up-regulates the intracellular production of nitric oxide in Chinese hamster ovary cell lines

We investigated the role of glycosaminoglycans (GAGs) in the regulation of endothelial nitric oxide synthase (eNOS) activity in wild‐type CHO‐K1 cells and in xylosyltransferase‐deficient CHO‐745 cells. GAGs inhibit the integrin/FAK/PI3K/AKT signaling pathway in CHO‐K1 cells, decreasing the phosphorylation of eNOS at Ser1177. Furthermore, in CHO‐K1 cells, eNOS and PKCα are localized at sphingolipid‐ and cholesterol‐rich domains in the plasma membrane called caveolae. At caveolae, PKCα activation stimulates the phosphorylation of eNOS on Thr495, resulting in further inhibition of NO production in these cells. In our data, CHO‐745 cells generate approximately 12‐fold more NO than CHO‐K1 cells. Increased NO production in CHO‐745 cells promotes higher rates of protein S‐nitrosylation and protein tyrosine nitration. Regarding reactive oxygen species (ROS) production, CHO‐745 cells show lower basal levels of superoxide (O2−) than CHO‐K1 cells. In addition, CHO‐745 cells express higher levels of GPx, Trx1, and catalase than CHO‐K1 cells, suggesting that CHO‐745 cells are in a constitutive nitrosative/oxidative stress condition. Accordingly, we showed that CHO‐745 cells are more sensitive to oxidant‐induced cell death than CHO‐K1 cells. The high concentration of NO and reactive oxygen species generated by CHO‐745 cells can induce simultaneous mitochondrial biogenesis and antioxidant gene expression. These observations led us to propose that GAGs are part of a regulatory mechanism that participates in eNOS activation and consequently regulates nitrosative/oxidative stress in CHO cells.

Abstract 1458: The precursor miR-138/2, but not miR-138/1, targets p53 mRNA and contributes to the acquisition of melanoma metastatic phenotype: Are the miRNAs precursors important to direct mature miRNA to mRNA targets

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA MiRNAs regulate pathways associated with differentiation, proliferation, apoptosis, among others, miRNAs missregulation may contribute to malignant transformation. Although melanoma is one of the rarest dermatological cancers, it is responsible for the greatest number of skin cancer-related deaths. In that context, our aim is to identify miRNAs that could be involved with melanoma progression. Using a cellular murine model of melanoma development, we identified the miR-138 as an interesting target of studying. In this model, four cell lines (melan-a, 4C, 4C11- and 4C11+) mimics the distinct steps of human melanoma genesis. miR-138 is codified from two different regions on the genome and they were named according to their origin. miR-138/1 is coded from chromosome 9 in mouse (corresponding to 3, in humans) while miR138/2 is coded from chromosome 8 in mouse (equivalent to 16, in humans). Despite the mature sequence of these two miRNAs being exactly the same, the flanking regions that form the precursors are distinct. miR-138 coded from chromosome 8 but not from chromosome 9 promotes cells to acquire a more aggressive phenotype. When we transfected the tumorigenic but non-metastatic cell line 4C11- with the genomic DNA corresponding to miR-138/2, it promotes the increase of proliferation, migration, colony formation and resistance to anoikis by this cell line compared to its untransfected counterpart 4C11-. In vivo assays showed that 4C11- miR-138/2 is able to form fast-growing tumors and pulmonary metastasis. None of these phenotypic changes was observed in 4C11- cells overexpressing the miR-138 coded from chromosome 9. We also validated p53 (rarely mutated in melanomas) as a target of miR-138 coded from chromosome 8, but not from chromosome 9. Therefore, we hypothesized that the sequence of precursor miRNA (pre-miR) could be involved with the direction of mature miRNA to the mRNA target. Moreover, EZH2, validated as a target of miR-138, is downregulated only in 4C11- cells overexpressing the miR-138/1, emphasizing even more the importance of the precursor sequence in the regulation of the mRNA target. miR-138 expression in melanocytic lesion were evaluated as well. We observed increased expression of miR-138 in primary and metastatic human melanoma samples related to benign nevi. Therefore, in this work we showed that miR-138 may contribute to melanoma genesis and is capable to regulate the expression of p53. Moreover, we suggest for the first time that the precursor sequence of miRNA can direct the mature miRNA to mRNA targets. Supported by CNPq and FAPESP Citation Format: Adriana Taveira Da Cruz, Aline Hunger, Genevieve Pare, Dulcie Lai, Fabiana Henriques Machado Melo, Bryan Eric Strauss, Victor Tron, Miriam Galvonas Jasiulionis. The precursor miR-138/2, but not miR-138/1, targets p53 mRNA and contributes to the acquisition of melanoma metastatic phenotype: Are the miRNAs precursors important to direct mature miRNA to mRNA targets. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1458. doi:10.1158/1538-7445.AM2014-1458