Role of adipose tissue in melanoma cancer microenvironment and progression.

BACKGROUND: An epidemiological association between excess weight and increased risk of cancer has been described in melanoma, for which the physiopathological mechanisms are still unknown. The study of tumor microenvironment and of the role of adipocytes in cancer development, progression and metastasis has recently received great interest. However, the role of peritumoral adipocytes has been characterized only in a few types of cancer, and in melanoma it still remains to be defined. METHODS: We investigated the interactions between adipocytes and melanoma cells using an in vitro co-culture system. We studied the morphological and functional properties of 3T3-L1 adipocytes before and after co-culture with A375 melanoma cells, in order to assess the role of adipocytes on melanoma migration. RESULTS: Morphological analysis showed that after 6 days of co-culture 3T3-L1 adipocytes were reduced in number and size. Moreover, we observed the appearance of dedifferentiated cells with a fibroblast-like phenotype that were not present in controls and that had lost the expression of some adipocyte-specific genes, and increased the expression of collagen, metalloproteinases and genes typical of dedifferentiation processes. Through the Matrigel Invasion Test, as well the Scratch Test, it was possible to observe that co-culture with adipocytes induced in melanoma cells increased migratory capacity, as compared with controls. In particular, the increase in migration observed in co-culture was suppressed after adding the protein SFRP-5 in the medium, supporting the involvement of the Wnt5a pathway. The activation of this pathway was further characterized by immunofluorescence and western blot analysis, showing in melanocytes in co-culture the activation of ß-catenin and LEF-1, two transcription factors involved in migration processes, neo-angiogenesis and metastasis. CONCLUSIONS: These data allow us to hypothesize a dedifferentiation process of adipocytes toward fibroblast-like cells, which can promote migration of melanoma cells through activation of Wnt5a and the intracellular pathways of ß-catenin and LEF-1.

Mechanisms of adipose tissue extracellular matrix alterations in an in vitro model of adipocytes hypoxia and aging.

Fibrosis has been considered as a hallmark of dysfunctional adipose tissue (AT), however the role and mechanisms of fibrosis in the age related AT dysfunction are not yet well characterized. The aim of the study was to investigate the mechanisms of extracellular matrix (ECM) alterations and the role of caveolins, using an in vitro model of adipocyte aging and hypoxia. Hypoxic adipocytes, but also aged adipocytes, were characterized by a significant increase in gene expression of pro-inflammatory cytokines and ECM components. Immunofluorescence analysis confirmed an increase in collagen VI-A3 in hypoxic and also in aged adipocytes. However aged adipocytes were characterized by only a slight increase in HIF1α immunofluorescence and by a more relevant increase in senescence compared to hypoxic and mature adipocytes, with an increase in p-53 protein and a decrease in SIRT 1 protein. Immunofluorescence and western blot analysis revealed a significant decrease in caveolin-1 expression in hypoxic adipocytes and even more in aged adipocytes. In conclusions, aging adipocytes are associated to alteration of ECM and fibrosis, by modulation of the caveolins through complex mechanisms where inflammation, hypoxia and cellular senescence are coexisting.

Aqueous extract of Arbutus unedo inhibits STAT1 activation in human breast cancer cell line MDA-MB-231 and human fibroblasts through SHP2 activation.

Arbutus unedo L. has been for a long time employed in traditional and popular medicine as an astringent, diuretic, urinary anti-septic, and more recently, in the therapy of hypertension and diabetes. Signal transducer and activator of transcription 1 (STAT1) is a fascinating and complex protein with multiple yet contrasting transcriptional functions. Although activation of this nuclear factor is finely regulated in order to control the entire inflammatory process, its hyper-activation or time-spatially erroneous activation may lead to exacerbation of inflammation. The modulation of this nuclear factor, therefore, has recently been considered as a new strategy in the treatment of inflammatory diseases. In this study, we present data showing that the aqueous extract of Arbutus unedo's leaves exerts inhibitory action on interferon-gamma (IFN-gamma) elicited activation of STAT1, both in human breast cancer cell line MDA-MB-231 and in human fibroblasts. This down-regulation of STAT1 is shown to result from a reduced tyrosine phosphorylation of STAT1 protein. Evidence is also presented indicating that the inhibitory effect of this extract may be mediated through enhancement of tyrosine phosphorylation of SHP2 tyrosine phosphatase. The modulation of this nuclear factor turns out into the regulation of the expression of a number of genes involved in the inflammatory response such as inducible nitric oxide synthase (iNOS) and intercellular adhesion molecule-1 (ICAM-1). Taken together, our results suggest that the employment of the Arbutus unedo aqueous extract is promising, at least, as an auxiliary anti-inflammatory treatment of diseases in which STAT1 plays a critical role.

Use of STAT1 inhibitors in the treatment of brain I/R injury and neurodegenerative diseases.

In the etiology of brain injury associated to ischemia/reperfusion (I/R) and neurodegenerative diseases, a critical involvement of excessive activation of signal transducer and activator of transcription 1 (STAT1) and successive induction of iNOS expression has widely been evidenced. Any compound capable to down-regulate STAT1 activation seems to represent a new, promising anti-inflammatory drug. Among plant compounds, only a few have shown to possess anti-STAT1 activity. Among them, epigallocatechin-3-gallate (EGCG), the main polyphenol present in green tea leaves, efficiently protects heart from I/R injury and this action is strictly correlated to its anti-STAT1 property. Hyperforin, the non-polyphenolic compound present in St. John's wort, attenuates β-cell death induced by interferon-γ (IFN-γ) by strongly down-regulating STAT1 activation. STAT1, therefore, seems to represent a new molecular target of the protective treatment also against brain injury associated to a number of brain pathologies. Either understanding the molecular mechanism of anti-STAT1 action of these compounds or identification of other anti-STAT1 compounds are urged.