MITF (microphthalmia-associated transcription factor) represents a melanocytic lineage-specific transcription factor whose role is profoundly extended in malignant melanoma. Over the last few years, the function of MITF has been tightly connected to plasticity of melanoma cells. MITF participates in executing diverse melanoma phenotypes defined by distinct gene expression profiles. Mutation-dependent alterations in MITF expression and activity have been found in a relatively small subset of melanomas. MITF activity is rather modulated by its upstream activators and suppressors operating on transcriptional, post-transcriptional and post-translational levels. These regulatory mechanisms also include epigenetic and microenvironmental signals. Several transcription factors and signaling pathways involved in the regulation of MITF expression and/or activity such as the Wnt/β-catenin pathway are broadly utilized by various types of tumors, whereas others, e.g., BRAFV600E/ERK1/2 are more specific for melanoma. Furthermore, the MITF activity can be affected by the availability of transcriptional co-partners that are often redirected by MITF from their own canonical signaling pathways. In this review, we discuss the complexity of a multilevel regulation of MITF expression and activity that underlies distinct context-related phenotypes of melanoma and might explain diverse responses of melanoma patients to currently used therapeutics.

WNT-signaling controls important cellular processes throughout embryonic development and adult life, so any deregulation of this signaling can result in a wide range of pathologies, including cancer. WNT-signaling is classified into two categories: β-catenin-dependent signaling (canonical pathway) and β-catenin-independent signaling (non-canonical pathway), the latter can be further divided into WNT/planar cell polarity (PCP) and calcium pathways. WNT ligands are considered as unique directional growth factors that contribute to both cell proliferation and polarity. Origin of cancer can be diverse and therefore tissue-specific differences can be found in WNT-signaling between cancers, including specific mutations contributing to cancer development. This review focuses on the role of the WNT-signaling pathway in melanoma. The current view on the role of WNT-signaling in cancer immunity as well as a short summary of WNT pathway-related drugs under investigation are also provided.

Reduced effectiveness of the most common antiplatelet drug, acetylsalicylic acid (ASA, aspirin), in diabetes mellitus has been associated with a lowered platelet sensitivity to ASA and related to glycemic control in diabetic patients. Our objectives were (a) to monitor the chemical background of how chronic hyperglycemia affects platelet response to ASA in diabetes and (b) to study a chemical competition between the amount of bound acetyl residues and the extent of protein glycation in blood platelets. Using whole-blood impedance aggregometry and platelet function analyzer (PFA-100) we observed a reduced platelet response to ASA in diabetic patients (14% vs. 79% for PFA-100 collagen-epinephrine occlusion time) and an association between the index of glycemic control and platelet refractoriness to ASA (r(S) = -0.378). Impaired platelet response to ASA was related to enhanced platelet protein glycation (3.6+/-0.4 in diabetes vs. 2.3+/-0.4 micromol fructosamine/microg protein in control) and reduced incorporation of acetyl residue into proteins of platelets from diabetic patients (47.4+/-2.0 in control vs. 33.1+/-0.7 micromol acetyl/microg protein in diabetic subjects). Incubation of blood platelets with increasing concentrations of glucose and ASA under in vitro conditions led to excessive modification in protein amino groups: glucose and ASA competed with each other in the course of nonenzymatic modifications, glycosylation, or acetylation, and their contributions to the occupancy of protein amino groups (R2 = 0.22 for glucose, R2 = 0.43 for ASA) were dependent upon the concentrations of glucose and ASA. Overall the effects of high glucose and high ASA on the overall occupancy of protein free amino groups are not additive. While at higher concentrations ASA overcomes the effects of hyperglycemia and retards glycation, high glucose makes acetylation less efficient, and therefore the resultant chemical modification becomes greatly reduced. In conclusion, diminished susceptibility of various platelet proteins and receptors on blood platelet membranes to acetylation and high ambient glucose might underlie the apparently differentiated sensitivity of blood platelets to ASA and determine platelet "insensitivity to aspirin" in diabetic patients.

Melanoma is a therapy-resistant skin cancer due to numerous mechanisms supporting cell survival. Although components of melanoma cytoprotective mechanisms are overexpressed in many types of tumors, some of their regulators are characteristic for melanoma. Several genes mediating pro-survival functions have been identified as direct targets of microphthalmia-associated transcription factor (MITF), a melanocyte-specific modulator also recognized as a lineage addiction oncogene in melanoma. BRAF(V600E) and other proteins deregulated in melanoma influence MITF expression and activity, or they are the partners of MITF in melanoma response to radiotherapy and chemotherapeutics. In this review, the pro-survival activity of MITF is discussed.

Melanomas contain subsets of cancer stem-like cells with tumor-initiating capacity. The frequency of these cells in the tumor is still a topic of debate. We investigated the phenotypic plasticity of cancer cells grown as melanospheres to elucidate the influence of the microenvironment on some features of melanoma stem-like cells. Cells from surgical specimens of nodular melanoma were grown as anchorage-independent melanospheres in a stem cell medium and as adherent monolayer cultures in the presence of serum. Proliferation and viability were measured by cell counting and an acid phosphatase assay; surface marker expression was evaluated by flow cytometry, and the clonogenic potential of single cells was assessed by growth in soft agar. Patient-derived melanoma cells could be maintained in cell culture for more than 16 months when grown as melanospheres. In the presence of serum, melanospheres completely changed their growth characteristics and formed adherent monolayers. The transition from melanospheres to monolayers was accompanied by an apparent loss of clonogenic potential, an increased proliferation rate, and altered expressions of cell surface markers ABCB5, CD133, and CD49f. These changes, however, were reversible. Compared with adherent monolayer cultures, melanospheres are enriched in cells with clonogenic potential, reflecting the self-renewing capacity of cancer stem-like cells. This clonogenic potential can be lost and regained depending on the growth conditions. Our results demonstrate how easily melanoma cells change their function upon exposure to external stimuli and suggest that the frequency of melanoma stem-like cells strongly depends on the microenvironment.