Low levels of mycophenolic acid induce differentiation of human neuroblastoma cell lines

Targeting of PHOX2B expression allows the identification of drugs effective in counteracting neuroblastoma cell growth

The pathogenic role of the PHOX2B gene in neuroblastoma is indicated by heterozygous mutations in neuroblastoma patients and by gene overexpression in both neuroblastoma cell lines and tumor samples.

PHOX2B encodes a transcription factor which is crucial for the correct development and differentiation of sympathetic neurons.

PHOX2B overexpression is considered a prognostic marker for neuroblastoma and it is also used by clinicians to monitor minimal residual disease. Furthermore, it has been observed that neuronal differentiation in neuroblastoma is dependent on down-regulation of PHOX2B expression, which confirms that PHOX2B expression may be considered a target in neuroblastoma.

Here, PHOX2B promoter or 3′ untranslated region were used as molecular targets in an in vitro high-throughput approach that led to the identification of molecules able to decrease PHOX2B expression at transcriptional and likely even at post-transcriptional levels. Further functional investigations carried out on PHOX2B mRNA levels and biological consequences, such as neuroblastoma cell apoptosis and growth, showed that chloroquine and mycophenolate mofetil are most promising agents for neuroblastoma therapy based on down-regulation of PHOX2B expression.

Finally, a strong correlation between the effect of drugs in terms of down-regulation of PHOX2B expression and of biological consequences in neuroblastoma cells confirms the role of PHOX2B as a potential molecular target in neuroblastoma.

The design, synthesis and in vitro immunosuppressive evaluation of novel isobenzofuran derivatives

The synthesis and biological evaluation of a series of novel isobenzofuran-based compounds are described. The compounds were evaluated for their immunosuppressive effects of T-cell proliferation and IMPDH type II inhibitor activity in vitro, as well as their structure-activity relationships were assessed. Several compounds demonstrated highly efficacious immunosuppressive properties, especially compounds 2d, 2e, 2h and 2j, which were superior to MPA, while compounds 2k, 2m, 2n, 4c and 5d exhibited an equipotent inhibitory activity compared to MPA. Generally, it was obviously demonstrated that α,β-unsaturated amides proved more potent than the diamide and urea series. The present study provides a guide for further research on development of safe and effective immunosuppressive agents.

Alterations in cytoskeletal protein expression by mycophenolic acid in human mesangial cells requires Rac inactivation

In response to glomerular injury, mesangial cells are activated into myofibroblasts, which contribute to the physiopathology of glomerulosclerosis. We have previously shown that chronic treatment of cultured human mesangial cells with mycophenolic acid (MPA), a specific inhibitor of guanosine nucleotide synthesis, prevents their activation and alters cytoskeleton protein expression and associated functions, such as contractility and migratory capacity. The aim of the present study was to explore the mechanisms underlying MPA-induced mesangial cytoskeleton alterations. We therein show that coincubation with guanosine (100 microM) compensates for the effects of MPA on mesangial cell proliferation and migration, and prevents MPA-induced overexpression of alpha-smooth muscle actin (SMA) and basic calponin (b-calp), indicating that guanylates are involved in mesangial responses to MPA. MPA decreased the GTP-bound (active) form of both RhoA, Rac1 and Cdc42, and specifically altered the expression level of Rac1. Pharmacological inhibition of RhoA activity reduced expression of both SMA and calponin, whereas overexpression of a dominant-negative form of Rac1 increased SMA expression. Conversely, overexpression of constitutively active Rac1 resulted in SMA and b-calp down-regulation, and fully prevented their stimulation by MPA, indicating that Rac inactivation is responsible for MPA effects on mesangial cytoskeletal expression. These results show that in human mesangial cells, RhoA and Rac1 exert opposite effects on the expression of two major cytoskeletal proteins: SMA and basic calponin. Moreover, these data highlight for the first time an integrated mechanism whereby MPA regulates mesangial phenotype, which is mediated by loss of Rac activity.

A Golgi study of neuronal architecture in a genetic mouse model for Lesch–Nyhan disease

Lesch-Nyhan disease (LND) is an inherited disorder associated with deficiency of hypoxanthine-guanine phosphoribosyltransferase (HPRT), an enzyme essential for purine recycling. The clinical manifestations of the disorder and several neurochemical studies have pointed towards a defect in the striatum, but histological studies of autopsied brain specimens have not revealed any consistent abnormalities. An HPRT-deficient (HPRT-) mouse that has been produced as a model for the disease also exhibits neurochemical abnormalities of the striatum without obvious histological correlates. In the current studies, Golgi-Cox histochemistry was used to evaluate the fine structure of medium spiny I neurons from the striatum in the HPRT- mice. To determine if any abnormalities might be restricted to striatal neurons, the pyramidal projection neurons of layer 5 of the cerebral cortex were also evaluated. Neurons from both regions demonstrated a normal distribution, orientation, and gross morphology. There was no evidence for an abnormal developmental process or degeneration. However, both regions demonstrated a paucity of neurons with very long dendrites and a reduction in dendritic spines that depended upon the distance from the cell body. These findings demonstrate that HPRT deficiency is associated with changes in neuronal architecture in the HPRT- mice. Similar abnormalities in the LND brain could underlie some of the clinical manifestations.

Guanylic nucleotide starvation affects Saccharomyces cerevisiae mother-daughter separation and may be a signal for entry into quiescence

Background

Guanylic nucleotides are both macromolecules constituents and crucial regulators for a variety of cellular processes. Therefore, their intracellular concentration must be strictly controlled. Consistently both yeast and mammalian cells tightly correlate the transcription of genes encoding enzymes critical for guanylic nucleotides biosynthesis with the proliferation state of the cell population.

Results

To gain insight into the molecular relationships connecting intracellular guanylic nucleotide levels and cellular proliferation, we have studied the consequences of guanylic nucleotide limitation on Saccharomyces cerevisiae cell cycle progression. We first utilized mycophenolic acid, an immunosuppressive drug that specifically inhibits inosine monophosphate dehydrogenase, the enzyme catalyzing the first committed step in de novo GMP biosynthesis. To approach this system physiologically, we next developed yeast mutants for which the intracellular guanylic nucleotide pools can be modulated through changes of growth conditions. In both the pharmacological and genetic approaches, we found that guanylic nucleotide limitation generated a mother-daughter separation defect, characterized by cells with two unseparated daughters. We then showed that this separation defect resulted from cell wall perturbations but not from impaired cytokinesis. Importantly, cells with similar separation defects were found in a wild type untreated yeast population entering quiescence upon nutrient limitation.

Conclusion

Our results demonstrate that guanylic nucleotide limitation slows budding yeast cell cycle progression, with a severe pause in telophase. At the cellular level, guanylic nucleotide limitation causes the emergence of cells with two unseparated daughters. By fluorescence and electron microscopy, we demonstrate that this phenotype arises from defects in cell wall partition between mother and daughter cells. Because cells with two unseparated daughters are also observed in a wild type population entering quiescence, our results reinforce the hypothesis that guanylic nucleotide intracellular pools contribute to a signal regulating both cell proliferation and entry into quiescence.