Molecular Biology and Genetic Mechanisms in the Progression of the Malignant Skin Melanoma

MicroRNA-340 is involved in ultraviolet B-induced pigmentation by regulating the MITF/TYRP1 axis

Objective

There is growing evidence that ultraviolet B (UVB) irradiation can change the expression profile of microRNAs (miRNAs) in immortalized human epidermal melanocytes (Pig-1). We aimed to investigate the effect of miR-340 on regulating UVB-induced pigmentation.

Methods

Real-time quantitative PCR (qRT-PCR) was used to evaluate the expression of miR-340 in Pig-1 cells. Immunoblotting analysis, qRT-PCR, and luciferase reporter assays were used to detect the potential target of miR-340. The sodium hydroxide dissolution assay was used to assess the effect of miR-340 on changes in melanin content.

Results

Expression of miR-340 was reduced in human Pig-1 cells after UVB irradiation. We found a negative correlation between miR-340 and melanocyte inducing transcription factor (MITF) in Pig-1 cells after UVB irradiation. Knockdown and overexpression of MITF in Pig-1 cells down- and upregulated melanogenesis, respectively. Overexpression of miR-340 inhibited MITF expression, reduced the amount of melanin, and suppressed expression of multiple key molecules involved in the pigment synthesis pathway, whereas knockdown of miR-340 showed the opposite results.

Conclusions

Our results showed that miR-340 inhibited melanogenesis by regulating the downstream molecules of MITF and its signaling pathways, suggested that miRNA-340 may be a new target for the clinical treatment of UVB-induced pigmentation.

Association of genetic variants of TMEM135 and PEX5 in the peroxisome pathway with cutaneous melanoma-specific survival

Background

Peroxisomes are ubiquitous and dynamic organelles that are involved in the metabolism of reactive oxygen species (ROS) and lipids. However, whether genetic variants in the peroxisome pathway genes are associated with survival in patients with melanoma has not been established. Therefore, our aim was to identify additional genetic variants in the peroxisome pathway that may provide new prognostic biomarkers for cutaneous melanoma (CM).

Methods

We assessed the associations between 8,397 common single-nucleotide polymorphisms (SNPs) in 88 peroxisome pathway genes and CM disease-specific survival (CMSS) in a two-stage analysis. For the discovery, we extracted the data from a published genome-wide association study from The University of Texas MD Anderson Cancer Center (MDACC). We then replicated the results in another dataset from the Nurse Health Study (NHS)/Health Professionals Follow-up Study (HPFS).

Results

Overall, 95 (11.1%) patients in the MDACC dataset and 48 (11.7%) patients in the NHS/HPFS dataset died of CM. We found 27 significant SNPs in the peroxisome pathway genes to be associated with CMSS in both datasets after multiple comparison correction using the Bayesian false-discovery probability method. In stepwise Cox proportional hazards regression analysis, with adjustment for other covariates and previously published SNPs in the MDACC dataset, we identified 2 independent SNPs (TMEM135 rs567403 C>G and PEX5 rs7969508 A>G) that predicted CMSS (P=0.003 and 0.031, respectively, in an additive genetic model). The expression quantitative trait loci analysis further revealed that the TMEM135 rs567403 GG and PEX5 rs7969508 GG genotypes were associated with increased and decreased levels of mRNA expression of their genes, respectively.

Conclusions

Once our findings are replicated by other investigators, these genetic variants may serve as novel biomarkers for the prediction of survival in patients with CM.

Melittin from Apis florea Venom as a Promising Therapeutic Agent for Skin Cancer Treatment

Melittin, a major component found in bee venom, is produced by the Apis species of the honey bee. In this study, the effect of melittin derived from Apis florea (Mel-AF), which is a wild honey bee species that is indigenous to Thailand, was investigated against human malignant melanoma (A375) cells. In this study, Mel-AF exhibited considerable potential in the anti-proliferative action of A375 cells. Subsequently, the cellular mechanism of Mel-AF that induced cell death was investigated in terms of apoptosis. As a result, gene and protein expression levels, which indicated the activation of cytochrome-c release and caspase-9 expression, eventually triggered the release of the caspase-3 executioner upon Mel-AF. We then determined that apoptosis-mediated cell death was carried out through the intrinsic mitochondrial pathway. Moreover, advanced abilities, including cell motility and invasion, were significantly suppressed. Mel-AF manipulated the actin arrangement via the trapping of stress fibers that were found underneath the membrane, which resulted in the defective actin cytoskeleton organization. Consequently, the expression of EGFR, a binding protein to F-actin, was also found to be suppressed. This outcome strongly supports the effects of Mel-AF in the inhibition of progressive malignant activity through the disruption of actin cytoskeleton-EGFR interaction and the EGFR signaling system. Thus, the findings of our current study indicate the potential usefulness of Mel-AF in cancer treatments as an apoptosis inducer and a potential actin-targeting agent.

MiR-497-5p, miR-195-5p and miR-455-3p function as tumor suppressors by targeting hTERT in melanoma A375 cells

Background

hTERT gene plays an important role in melanoma, although the specific mechanism involved is unclear. The aim of this study was to screen and identify the relative miRNAs with the regulation of hTERT in melanoma.

Materials and methods

Quantitative real-time polymerase chain reaction (q-PCR) and immunohistochemistry were performed to detect hTERT mRNA and protein expression in 36 formalin-fixed paraffin-embedded melanoma tissues and 36 age- and sex-matched pigmented nevi cases, respectively. Bioinformatics analysis and custom miRNA polymerase chain reaction array were determined for predicting, screening and verifying miRNAs with the regulation of the hTERT gene. To investigate the biological functions, miRNAs mimics or inhibitors were transfected into melanoma A375 cells. The relative expression of miR-497-5p, miR-195-5p, miR-455-3p and hTERT mRNA was determined by q-PCR. The protein expression of hTERT was detected by Western blot. 3-(4,5-Dimethylthiazolyl-2-yl)-2,5-biphenyl tetrazolium bromide and flow cytometry were employed to detect cell proliferation ability, cell apoptosis and cell cycle. Transwell and wound healing assays were used to observe cell invasion and migration abilities. A direct target gene of miRNAs was analyzed by a dual luciferase reporter activity assay.

Results

MiR-497-5p, miR-195-5p, miR-455-3p were significantly downregulated, while hTERT was upregulated in melanoma tissues. hTERT expression level was inversely correlated with miR-497-5p, miR-195-5p and miR-455-3p. Overexpression of miR-497-5p, miR-195-5p and miR-455-3p inhibited A375 cell proliferation, migration and invasion, arrested the cell cycle, induced cell apoptosis and decreased hTERT expression at both mRNA and protein levels. Suppression of miR-497-5p, miR-195-5p and miR-455-3p partially reversed the inhibitory effects. Finally, hTERT was identified as a direct target of miR-497-5p, miR-195-5p and miR-455-3p.

Conclusions

MiR-497-5p, miR-195-5p and miR-455-3p act as tumor suppressors by targeting hTERT in melanoma A375 cells. Therefore, miR-497-5p, miR-195-5p and miR-455-3p could be potential targeted therapeutic choice for melanoma.

Genetic variants in the metzincin metallopeptidase family genes predict melanoma survival

Metzincins are key molecules in the degradation of the extracellular matrix and play an important role in cellular processes such as cell migration, adhesion, and cell fusion of malignant tumors, including cutaneous melanoma (CM). We hypothesized that genetic variants of the metzincin metallopeptidase family genes would be associated with CM-specific survival (CMSS). To test this hypothesis, we first performed Cox proportional hazards regression analysis to evaluate the associations between genetic variants of 75 metzincin metallopeptidase family genes and CMSS using the dataset from the genome-wide association study (GWAS) from The University of Texas MD Anderson Cancer Center (MDACC) which included 858 non-Hispanic white patients with CM, and then validated using the dataset from the Harvard GWAS study which had 409 non-Hispanic white patients with invasive CM. Four independent SNPs (MMP16 rs10090371 C>A, ADAMTS3 rs788935 T>C, TLL2 rs10882807 T>C and MMP9 rs3918251 A>G) were identified as predictors of CMSS, with a variant-allele attributed hazards ratio (HR) of 1.73 (1.32-2.29, 9.68E-05), 1.46 (1.15-1.85, 0.002), 1.68 (1.31-2.14, 3.32E-05) and 0.67 (0.51-0.87, 0.003), respectively, in the meta-analysis of these two GWAS studies. Combined analysis of risk genotypes of these four SNPs revealed a decreased CMSS in a dose-response manner as the number of risk genotypes increased (P_trend < 0.001). An improvement was observed in the prediction model (area under the curve [AUC] = 81.4% vs. 78.6%), when these risk genotypes were added to the model containing non-genotyping variables. Our findings suggest that these genetic variants may be promising prognostic biomarkers for CMSS.

Role Played by Signalling Pathways in Overcoming BRAF Inhibitor Resistance in Melanoma

The discovery of the BRAF^V600E mutation led to the development of vemurafenib (PLX4032), a selective BRAF inhibitor specific to the kinase, for the treatment of metastatic melanomas. However, initial success of the drug was dampened by the development of acquired resistance. Melanoma was shown to relapse in patients following treatment with vemurafenib which eventually led to patients' deaths. It has been proposed that mechanisms of resistance can be due to (1) reactivation of the mitogen-activated protein kinase (MAPK) signalling pathway via secondary mutations, amplification or activation of target kinase(s), (2) the bypass of oncogenic pathway via activation of alternative signalling pathways, (3) other uncharacterized mechanisms. Studies showed that receptor tyrosine kinases (RTK) such as PDGFRβ, IGF1R, EGFR and c-Met were overexpressed in melanoma cells. Along with increased secretion of growth factors such as HGF and TGF-α, this will trigger intracellular signalling cascades. This review discusses the role MAPK and Phosphatidylinositol-3-kinase-protein kinase B-mammalian target of rapamycin (PI3K-AKT-mTOR) pathways play in the mechanism of resistance of melanomas.