TRPM7 and MagT1 regulate the proliferation of osteoblast-like SaOS-2 cells through different mechanisms.

A correct magnesium (Mg2+) intake is essential for bone health. In particular, Mg2+ deficiency inhibits the proliferation of osteoblast-like SaOS-2 cells by increasing nitric oxide (NO) production through the upregulation of inducible NO synthase. At the moment, little is known about the expression and the role of TRPM7, a channel/enzyme involved in Mg2+ uptake, and MagT1, a Mg2+ selective transporter, in SaOS-2 cells. Here, we demonstrate that TRPM7 is not modulated by different extracellular concentrations of Mg2+ and its silencing exacerbates growth inhibition exerted by low Mg2+ through the activation of inducible NO synthase and consequent accumulation of NO. Moreover, MagT1 is upregulated in SaOS-2 cultured in high Mg2+ and its silencing inhibits the growth of SaOS-2 cultured in media containing physiological or high Mg2+, without any modulation of NO production. We propose that TRPM7 and MagT1 are both involved in regulating SaOS-2 proliferation through different mechanisms.

Impact of extracellular HIV-TAT on the regulation of EDF-1 levels in human endothelial cells.

EDF-1 has been isolated by RNA fingerprinting from human endothelial cells exposed to human immunodeficiency virus type 1 (HIV-) Tat, a viral protein known to function as a cytokine in the activation of endothelial cells. Here we provide the molecular evidence that the inhibition of EDF-1 mRNA is transcriptionally regulated in human endothelial cells. Indeed, HIV-Tat inhibits the luciferase activity of endothelial cells transiently transfected with a construct containing 2300 bp of EDF-1 promoter cloned upstream of a luciferase reporter system. The decrease of EDF-1 RNA, however, does not translate into any alteration at the protein level, even when the cells are exposed to MG132, a proteasome inhibitor. Analogously, no modulation of the total amounts of EDF-1 by HIV-Tat has been observed in the presence of pro-inflammatory cytokine interleukin 1beta, which induces endothelial responsiveness to the in vitro effects of HIV-Tat. We have previously shown that EDF-1 is cytosolic and can be translocated to the nucleus upon activation of protein kinases A and C. In response to HIV-Tat, EDF-1 is mainly in the cytosol. Since cytosolic EDF-1 binds and sequesters calmodulin, an important regulator of endothelial nitric oxide synthase, these results might explain why we do not observe any induction of nitric oxide in endothelial cells exposed to HIV-Tat.

Magnesium and neoplasia: from carcinogenesis to tumor growth and progression or treatment.

Magnesium is involved in a wide range of biochemical reactions that are crucial to cell proliferation, differentiation, angiogenesis, and apoptosis. Changes in magnesium availability have been shown to influence biological responses of immuno-inflammatory cells. Equally plausible seems to be an involvement of magnesium in the multistep and interconnected processes that lead to tumor formation and development; however, the "how" and "when" of such an involvement remain to be defined. Here, we reviewed in vitro and in vivo data that indicated a role for magnesium in many biological and clinical aspects of cancer (from neoplastic transformation to tumor growth and progression or pharmacologic treatment). In adopting this approach we went through a full circle from molecular aspects to observational or epidemiological studies that could reconcile in a unifying picture the otherwise fragmentary or puzzling data currently available on the role of magnesium in cancer.

Impact of simulated microgravity on cell cycle control and cytokine release by U937 cells.

Previous experiments from flight- and ground-based model systems indicate unexpected alterations of human leukocytes, leading to growth retardation and depression of mitogenic activation. The response of myelomonocytic U937 cells to simulated microgravity was therefore investigated. To this purpose, U937 cells were cultured in the NASA-developed bioreactor Rotating Wall Vessel (RWV) as a device to simulate microgravity on earth. No apoptosis was detected, in part because of the up-regulation of hsp70. In agreement with results obtained in space-flown U937 cells, the cells grew more slowly in the RWV than under normal conditions and this correlated with the down-modulation of cdc25B. Marked alterations of the cytokine secretion profile and, in particular, of inflammatory chemokines, as well as a decrease of the proteasome activity, were also observed in response to microgravity.

The dual role of endothelial differentiation-related factor-1 in the cytosol and nucleus: modulation by protein kinase A.

Endothelial differentiation-related factor (EDF)-1 is involved in the repression of endothelial cell differentiation and is the first studied calmodulin (CaM)-binding protein in endothelial cells. Here we report that (i) EDF-1 is in vitro and in vivo phosphorylated by protein kinase A (PKA); (ii) EDF-1/CaM interaction is modulated by the phosphorylation of EDF-1 by PKA; (iii) forskolin stimulates nuclear accumulation of EDF-1, and (iv) PKA phosphorylation enhances EDF-1 interaction with the TATA-binding protein. CaM modulates the activity of several enzymes, among which is nitric oxide synthase (NOS). EDF-1, but not phosphorylated EDF-1, inhibits the activity of NOS. Accordingly, we detected an increase in NOS activity in cells that express low amounts of EDF-1. Our results indicate that EDF-1 serves two main functions in endothelial cells: (i) it regulates CaM availability in the cytosol, and (ii) it acts in the nucleus as a transcriptional coactivator.