Sara Castiglioni

Magnesium and Osteoporosis: Current State of Knowledge and Future Research Directions

A tight control of magnesium homeostasis seems to be crucial for bone health. On the basis of experimental and epidemiological studies, both low and high magnesium have harmful effects on the bones. Magnesium deficiency contributes to osteoporosis directly by acting on crystal formation and on bone cells and indirectly by impacting on the secretion and the activity of parathyroid hormone and by promoting low grade inflammation. Less is known about the mechanisms responsible for the mineralization defects observed when magnesium is elevated. Overall, controlling and maintaining magnesium homeostasis represents a helpful intervention to maintain bone integrity.

The PPAR-γ agonist troglitazone antagonizes survival pathways induced by STAT-3 in recombinant interferon-β treated pancreatic cancer cells.

We have previously shown that cancer cells can protect themselves from apoptosis induced by type I interferons (IFNs) through a ras→MAPK-mediated pathway. In addition, since IFN-mediated signalling components STATs are controlled by PPAR gamma we studied the pharmacological interaction between recombinant IFN-β and the PPAR-γ agonist troglitazone (TGZ). This combination induced a synergistic effect on the growth inhibition of BxPC-3, a pancreatic cancer cell line, through the counteraction of the IFN-β-induced activation of STAT-3, MAPK and AKT and the increase in the binding of both STAT-1 related complexes and PPAR-γ with specific DNA responsive elements. The synergism on cell growth inhibition correlated with a cell cycle arrest in G0/G1 phase, secondary to a long-lasting increase of both p21 and p27 expressions. Blockade of MAPK activation and the effect on p21 and p27 expressions, induced by IFN-β and TGZ combination, were due to the decreased activation of STAT-3 secondary to TGZ. IFN-β alone also increased p21 and p27 expression through STAT-1 phosphorylation and this effect was attenuated by the concomitant activation of IFNbeta-induced STAT-3-activation. The combination induced also an increase in autophagy and a decrease in anti-autophagic bcl-2/beclin-1 complex formation. This effect was mediated by the inactivation of the AKT→mTOR-dependent pathway. To the best of our knowledge this is the first evidence that PPAR-γ activation can counteract STAT-3-dependent escape pathways to IFN-β-induced growth inhibition through cell cycle perturbation and increased autophagic death in pancreatic cancer cells.

Regulation and Function of TRPM7 in Human Endothelial Cells: TRPM7 as a Potential Novel Regulator of Endothelial Function

TRPM7, a cation channel of the transient receptor potential channel family, has been identified as a ubiquitous magnesium transporter. We here show that TRPM7 is expressed in endothelial cells isolated from the umbilical vein (HUVEC), widely used as a model of macrovascular endothelium. Quiescence and senescence do not modulate TRPM7 amounts, whereas oxidative stress generated by the addition of hydrogen peroxide increases TRPM7 levels. Moreover, high extracellular magnesium decreases the levels of TRPM7 by activating calpains, while low extracellular magnesium, known to promote endothelial dysfunction, stimulates TRPM7 accumulation partly through the action of free radicals. Indeed, the antioxidant trolox prevents TRPM7 increase by low magnesium. We also demonstrate the unique behaviour of HUVEC in responding to pharmacological and genetic inhibition of TRPM7 with an increase of cell growth and migration. Our results indicate that TRPM7 modulates endothelial behavior and that any condition leading to TRPM7 upregulation might impair endothelial function.

HD-PTP inhibits endothelial migration through its interaction with Src

Endothelial migration, early step in angiogenesis, is tightly regulated by the coordinated action of tyrosine kinases and tyrosine phosphatases. HD-PTP contributes to endothelial motility, since endothelial cells silencing HD-PTP after transfection with iRNA acquire a scattered and spindle-shaped phenotype and migrate faster than controls. Since (i) the proto-oncogene Src contributes to the regulation of cell motility and (ii) HD-PTP has a potential binding site for Src, we investigated whether an interplay exists between these two proteins. We found that Src binds HD-PTP and this interaction is enhanced after exposure to basic fibroblast growth factor. While HD-PTP does not modulate the levels of Src phosphorylation both in vitro and in vivo, we found that Src phosphorylates HD-PTP on tyrosine residues. Here we show for the first time that (i) HD-PTP has a tyrosine phosphatase activity; (ii) HD-PTP phosphorylation by Src inhibits its enzymatic activity. Interestingly, pharmacological and genetic inhibition of Src abrogates the migratory phenotype of endothelial cells silencing HD-PTP. On these bases, and because we have previously demonstrated that HD-PTP binds and dephosphorylates focal adhesion kinase (FAK), another crucial regulator of cell migration, we hypothesize that HD-PTP participates to the regulation of endothelial motility through its interactions with Src and FAK.

Magnesium and cancer: a dangerous liason

A complex relationship links magnesium and cancer. The aim of this review is to revisit current knowledge concerning the contribution of magnesium to tumorigenesis, from transformed cells to animal models, and ending with data from human studies. Cultured neoplastic cells tend to accumulate magnesium. High intracellular levels of the cation seem to confer a metabolic advantage to the cells, contribute to alterations of the genome, and promote the acquisition of an immortal phenotype. In magnesium-deficient mice, low magnesium both limits and fosters tumorigenesis, since inhibition of tumor growth at its primary site is observed in the face of increased metastatic colonization. Epidemiological studies identify magnesium deficiency as a risk factor for some types of human cancers. In addition, impaired magnesium homeostasis is reported in cancer patients, and frequently complicates therapy with some anti-cancer drugs. More studies should be undertaken in order to disclose whether a simple and inexpensive intervention to optimize magnesium intake might be helpful in the prevention and treatment of cancer.

Iterleukin 1 alpha is a marker of endothelial cellular senescent

BackgroundThe functional changes associated with endothelial senescence may be involved in human aging and age-related vascular disorders. Since the inflammatory cytokine interleukin (IL-)1 inhibits endothelial growth, we evaluated the expression of IL-1α, IL-1β and their antagonist, the IL-1 receptor antagonist (IL-1ra), in endothelial in vitro senescence and quiescence. We also examined the expression of IL-1α in human senescent and progeric fibroblasts.ResultsWe found that the overexpression of IL-1α specifically characterizes endothelial senescence. No modulation of this cytokine was observed in endothelial quiescence and in senescent or progeric human fibroblasts. The expression of IL-1β and IL-1ra was also assessed and found not to be affected by senescence.ConclusionOur results indicate that a dysfunction of the cytokine network associates with aging and point to a specific role of IL-1α in endothelial senescence.

Inhibition of T24 human bladder carcinoma cell migration by RNA interference suppressing the expression of HD-PTP

Cell migration is fundamental for invasion and metastasis and is modulated by the reversible phosphorylation of tyrosine residues on target proteins. Here we report that the tyrosine phosphatase HD-PTP has a role in modulating the motility of T24 bladder carcinoma cells. Indeed, HD-PTP silencing by RNA interference (RNAi) markedly induced cell migration in a Src dependent fashion. We therefore investigated the interaction and the regulation of Src and HD-PTP. We found that, in Epidermal Growth Factor (EGF) stimulated cells, Src binds to and phosphorylates HD-PTP on tyrosine residues. On the contrary, HD-PTP does not modulate the levels of Src phosphorylation. Interestingly, HD-PTP also binds to FAK, another regulator of cell migration, and this interaction is inhibited after exposure to EGF. FAK phosphorylates HD-PTP and this event reduced the interactions between the two proteins. Interestingly, in cells silencing HD-PTP the phosphorylation of FAK is enhanced and this correlates with its localization in focal complexes both in the presence and in the absence of EGF. We hypothesize that in unstimulated T24 cells HD-PTP does not interact with Src, while it binds to FAK. Following stimulation with EGF, HD-PTP is tyrosine-phosphorylated and releases FAK which will ultimately contribute to the turn-over of focal adhesion and, therefore, to cell motility.

Type I Interferons : Ancient Peptides with Still Under-Discovered Anti-Cancer Properties

Type I interferons (IFNs) represent a group of cytokines that act through a common receptor composed by two chains (IFNAR-1 and IFNAR-2). Several in vitro and in vivo studies showed a potent antitumor activity induced by these cytokines. IFN-α, the first cytokine to be produced by recombinant DNA technology, has emerged as an important regulator of cancer cell growth and differentiation, affecting cellular communication and signal transduction pathways. IFN-α, is currently the most used cytokine in the treatment of cancer. However, the potential anti-tumour activity of IFN-α is limited by the activation of tumour resistance mechanisms. This article reviews the current knowledge about the antitumor activity of type I IFNs, focusing on new potential strategies able to strengthen the antitumor activity of these cytokines.

Silver nanoparticles-induced cytotoxicity requires ERK activation in human bladder carcinoma cells

Silver nanoparticles are toxic both in vitro and in vivo. We have investigated the possibility to exploit the cytotoxic potential of silver nanoparticles in T24 bladder carcinoma cells using both bare and PolyVinylPyrrolidone-coated silver nanoparticles. We show that the two types of silver nanoparticles promote morphological changes and cytoskeletal disorganization, are cytotoxic and induce cell death. These effects are due to the increased production of reactive oxygen species which are responsible, at least in part, for the sustained activation of ERK1/2. Indeed, both cytotoxicity and ERK1/2 activation are prevented by exposing the cells to the anti-oxidant N-acetylcysteine. Also blocking the ERK1/2 pathway with the MEK inhibitor PD98059 protects the cells from nanoparticles cytotoxicity. Our findings suggest that ERK activation plays a role in silver nanoparticle-mediated cytotoxicity in T24 cells.

Magnesium homeostasis in colon carcinoma LoVo cells sensitive or resistant to doxorubicin

Neoplastic cells accumulate magnesium, an event which provides selective advantages and is frequently associated with TRPM7overexpression. Little is known about magnesium homeostasis in drug-resistant cancer cells. Therefore, we used the colon cancer LoVo cell model and compared doxorubicin-resistant to sensitive cells. In resistant cells the concentration of total magnesium is higher while its influx capacity is lower than in sensitive cells. Accordingly, resistant cells express lower amounts of the TRPM6 and 7, both involved in magnesium transport. While decreased TRPM6 levels are due to transcriptional regulation, post-transcriptional events are involved in reducing the amounts of TRPM7. Indeed, the calpain inhibitor calpeptin markedly increases the levels of TRPM7 in resistant cells. In doxorubicin-sensitive cells, silencing TRPM7 shifts the phenotype to one more similar to resistant cells, since in these cells silencing TRPM7 significantly decreases the influx of magnesium, increases its intracellular concentration and increases resistance to doxorubicin. On the other hand, calpain inhibition upregulates TRPM7, decreases intracellular magnesium and enhances the sensitivity to doxorubicin of resistant LoVo cells. We conclude that in LoVo cells drug resistance is associated with alteration of magnesium homeostasis through modulation of TRPM7. Our data suggest that TRPM7 expression may be an additional undisclosed player in chemoresistance.