Human glioblastoma ADF cells express tyrosinase, L-tyrosine hydroxylase and melanosomes and are sensitive to L-tyrosine and phenylthiourea

The miR-144/Hmgn2 regulatory axis orchestrates chromatin organization during erythropoiesis

Differentiation of stem and progenitor cells is a highly regulated process that involves the coordinated action of multiple layers of regulation. Here we show how the post-transcriptional regulatory layer instructs the level of chromatin regulation via miR-144 and its targets to orchestrate chromatin condensation during erythropoiesis. The loss of miR-144 leads to impaired chromatin condensation during erythrocyte maturation. Among the several targets of miR-144 that influence chromatin organization, the miR-144-dependent regulation of Hmgn2 is conserved from fish to humans. Our genetic probing of the miR-144/Hmgn2 regulatory axis establish that intact miR-144 target sites in the Hmgn2 3'UTR are necessary for the proper maturation of erythrocytes in both zebrafish and human iPSC-derived erythroid cells while loss of Hmgn2 rescues in part the miR-144 null phenotype. Altogether, our results uncover miR-144 and its target Hmgn2 as the backbone of the genetic regulatory circuit that controls the terminal differentiation of erythrocytes in vertebrates.

p44/42 MAPK signaling is a prime target activated by phenylethyl resorcinol in its anti-melanogenic action

BACKGROUND

Melanin plays a crucial role in protecting human skin against exposure to ultraviolet (UV) radiation. However, its overproduction induces hyperpigmentation disorders of the skin.

PURPOSE

To investigate effects of phenylethyl resorcinol as one resorcinol derivative on melanogenesis and its mechanisms using B16F10 mouse melanoma cells and human epidermal melanocytes.

METHODS

Effects of phenylethyl resorcinol on melanogenesis and its mechanism of action were examined using several in vitro assays (i.e., cell survival, melanin content, cellular tyrosinase activity, real-time PCR analysis, luciferase-reporter assay, Western blot analysis, and ELISAs for cyclic AMP (cAMP), protein kinase A (PKA), cAMP response element binding (CREB) protein, and mitogen-activated protein kinases (MAPKs)).

RESULTS

Phenylethyl resorcinol reduced both melanin content and tyrosinase activity in these cells. Phenylethyl resorcinol also suppressed tyrosinase activity in cell-free tyrosinase enzyme assay. Although phenylethyl resorcinol decreased mRNA levels of tyrosinase and tyrosinase-related protein (TRP)-2, it did not affect mRNA levels of melanogenic gene microphthalmia-associated transcriptional factor (MITF) or TRP-1. Phenylethyl resorcinol had no effects on cAMP signaling or NF-κB signaling based on results of cyclic AMP response element (CRE)-luciferase reporter assay, cAMP production, protein kinase A (PKA) activity, Western blot assays for phosphorylated CRE-binding protein (CREB), NF-κB-luciferase reporter assay, and Western blot assays for phosphorylated NF-κB. However, phenylethyl resorcinol induced activation of activator protein-1 (AP-1) signaling. Specifically, phenylethyl resorcinol increased AP-1 reporter activity and increased phosphorylation of p44/42 MAPK, but not p38 MAPK or c-Jun N-terminal kinase (JNK). MEK1/2 and Src, upstream molecules of p44/42 MAPK were also phosphorylated by phenylethyl resorcinol. In addition, phenylethyl resorcinol-induced decreases in melanin content, tyrosinase activity, and MITF protein levels were attenuated by PD98059, a p44/42 MAPK inhibitor.

CONCLUSION

These data indicate that the anti-melanogenic activity of phenylethyl resorcinol is mediated by activation of p44/42 MAPK, indicating that phenylethyl resorcinol may be a potential therapeutic agent for treating hyperpigmentation skin disorders.

Exploiting Tyrosinase Expression and Activity in Melanocytic Tumors

Melanoma is an aggressive tumor that expresses the pigmentation enzyme tyrosinase. Tyrosinase expression increases during tumorigenesis, which could allow for selective treatment of this tumor type by strategies that use tyrosinase activity. Approaches targeting tyrosinase would involve gene transcription or signal transduction pathways mediated by p53 in a direct or indirect manner. Two pathways are proposed for exploiting tyrosinase expression: ( a) a p53-dependent pathway leading to apoptosis or arrest and ( b) a reactive oxygen species–mediated induction of endoplasmic reticulum stress in p53 mutant tumors. Both strategies could use tyrosinase-mediated activation of quercetin, a dietary polyphenol that induces the expression of p53 and modulates reactive oxygen species. In addition to antitumor signaling properties, activation of quercetin could complement conventional cancer therapy by the induction of phase II detoxification enzymes resulting in p53 stabilization and transduction of its downstream targets. In conclusion, recent advances in tyrosinase enzymology, prodrug chemistry, and modern chemotherapeutics present an intriguing and selective multitherapy targeting system where dietary bioflavonoids could be used to complement conventional cancer treatments.

PPAR Gamma in Neuroblastoma: The Translational Perspectives of Hypoglycemic Drugs

Neuroblastoma (NB) is the most common and aggressive pediatric cancer, characterized by a remarkable phenotypic diversity and high malignancy. The heterogeneous clinical behavior, ranging from spontaneous remission to fatal metastatic disease, is attributable to NB biology and genetics. Despite major advances in therapies, NB is still associated with a high morbidity and mortality. Thus, novel diagnostic, prognostic, and therapeutic approaches are required, mainly to improve treatment outcomes of high-risk NB patients. Among neuroepithelial cancers, NB is the most studied tumor as far as PPAR ligands are concerned. PPAR ligands are endowed with antitumoral effects, mainly acting on cancer stem cells, and constitute a possible add-on therapy to antiblastic drugs, in particular for NB with unfavourable prognosis. While discussing clinical background, this review will provide a synopsis of the major studies about PPAR expression in NB, focusing on the potential beneficial effects of hypoglycemic drugs, thiazolidinediones and metformin, to reduce the occurrence of relapses as well as tumor regrowth in NB patients.

p47phox and reactive oxygen species production modulate expression of microRNA-451 in macrophages

The production of microRNAs (miRNA) is influenced by various stimuli, including environmental stresses. We hypothesized that reactive oxygen species (ROS)-associated stress could regulate macrophage miRNA synthesis. miRNAs undergo unique steps of maturation processing through either one of two pathways of cytoplasmic processing. Unlike the canonical pathway, the regulation of alternative cytoplasmic processing of miRNA has not been fully elucidated yet. We cultured bone marrow derived macrophages (BMDM) from wild type (WT) and p47(phox-/-) mice and profiled miRNA expression using microarrays. We analyzed 375 miRNAs including four endogenous controls to normalize the data. At resting state, p47(phox-/-) BMDM has the markedly reduced expression of miR-451 compared to WT BMDM, without other significant differences. Unlike majority of miRNAs, miR-451 goes through the unique alternative processing pathway, in which Ago2 plays a key role. In spite of significant reduction of mature miR-451, however, its precursor form, pre-mir-451, was similar in both BMDMs, suggesting that the processing of pre-mir-451 is impaired in p47(phox-/-) BMDM. Moreover, p47(phox-/-) BMDM expressed significantly reduced level of Ago2. In contrast, Ago2 mRNA levels were similar in WT and p47(phox-/-) BMDM, suggesting a post-transcriptional defect of Ago2 production in p47(phox-/-) macrophages, which resulted in impaired processing of pre-miR-451. In order to examine the functional significance of miR-451 in macrophages, we cultured BMDMs from miR-451 knock-out mice. Of interest, miR-451-deficient BMDM exhibited reduced ROS generation upon zymosan stimulation, compared to WT BMDM. Our studies suggest functional crosstalk between ROS and miR-451 in the regulation of macrophage oxidant stress.

Peroxisome Proliferator-Activated Receptors (PPARs) as Potential Inducers of Antineoplastic Effects in CNS Tumors

The peroxisome proliferator-activated receptors (PPARs) are ligand-inducible transcription factors which belong to the superfamily of nuclear hormone receptors. In recent years it turned out that natural as well as synthetic PPAR agonists exhibit profound antineoplastic as well as redifferentiation effects in tumors of the central nervous system (CNS). The molecular understanding of the underlying mechanisms is still emerging, with partially controverse findings reported by a number of studies dealing with the influence of PPARs on treatment of tumor cells in vitro. Remarkably, studies examining the effects of these drugs in vivo are just beginning to emerge. However, the agonists of PPARs, in particular the thiazolidinediones, seem to be promising candidates for new approaches in human CNS tumor therapy.

The phenylthiourea is a competitive inhibitor of the enzymatic oxidation of DOPA by phenoloxidase

Phenoloxidase is a key enzyme of melanization catalyzing the oxidation of phenols. Phenylthiourea (PTU) is the well-known and widely used inhibitor of phenoloxidase. However, the mechanism of its action is not quite clear. In the present work, the effect of PTU on the enzymatic oxidation of 3-(3,4-dihydroxyphenyl)-l-alanine (DOPA) by phenoloxidase was studied by spectrophotometric methods. The inhibition constant of PTU was estimated as 0.21 ± 0.09 µM and the competitive type of inhibition was determined for this reaction.

miR-451 protects against erythroid oxidant stress by repressing 14-3-3zeta

The bicistronic microRNA (miRNA) locus miR-144/451 is highly expressed during erythrocyte development, although its physiological roles are poorly understood. We show that miR-144/451 ablation in mice causes mild erythrocyte instability and increased susceptibility to damage after exposure to oxidant drugs. This phenotype is deeply conserved, as miR-451 depletion synergizes with oxidant stress to cause profound anemia in zebrafish embryos. At least some protective activities of miR-451 stem from its ability to directly suppress production of 14-3-3zeta, a phospho-serine/threonine-binding protein that inhibits nuclear accumulation of transcription factor FoxO3, a positive regulator of erythroid anti-oxidant genes. Thus, in miR-144/451(-/-) erythroblasts, 14-3-3zeta accumulates, causing partial relocalization of FoxO3 from nucleus to cytoplasm with dampening of its transcriptional program, including anti-oxidant-encoding genes Cat and Gpx1. Supporting this mechanism, overexpression of 14-3-3zeta in erythroid cells and fibroblasts inhibits nuclear localization and activity of FoxO3. Moreover, shRNA suppression of 14-3-3zeta protects miR-144/451(-/-) erythrocytes against peroxide-induced destruction, and restores catalase activity. Our findings define a novel miRNA-regulated pathway that protects erythrocytes against oxidant stress, and, more generally, illustrate how a miRNA can influence gene expression by altering the activity of a key transcription factor.