S-sulfhydration/desulfhydration and S-nitrosylation/denitrosylation: a common paradigm for gasotransmitter signaling by H2S and NO.

Sulfhydryl groups on protein Cys residues undergo an array of oxidative reactions and modifications, giving rise to a virtual redox zip code with physiological and pathophysiological relevance for modulation of protein structure and functions. While over two decades of studies have established NO-dependent S-nitrosylation as ubiquitous and fundamental for the regulation of diverse protein activities, proteomic methods for studying H2S-dependent S-sulfhydration have only recently been described and now suggest that this is also an abundant modification with potential for global physiological importance. Notably, protein S-sulfhydration and S-nitrosylation bear striking similarities in terms of their chemical and biological determinants, as well as reversal of these modifications via group-transfer to glutathione, followed by the removal from glutathione by enzymes that have apparently evolved to selectively catalyze denitrosylation and desulfhydration. Here we review determinants of protein and low-molecular-weight thiol S-sulfhydration/desulfhydration, similarities with S-nitrosylation/denitrosylation, and methods that are being employed to investigate and quantify these gasotransmitter-mediated cell signaling systems.

Hypoxia- and vascular endothelial growth factor-induced stromal cell-derived factor-1alpha/CXCR4 expression in glioblastomas: one plausible explanation of Scherer's structures.

The morphological patterns of glioma cell invasion are known as the secondary structures of Scherer. In this report, we propose a biologically based mechanism for the nonrandom formation of Scherer's secondary structures based on the differential expression of stromal cell-derived factor (SDF)-1alpha and CXCR4 at the invading edge of glioblastomas. The chemokine SDF-1alpha was highly expressed in neurons, blood vessels, subpial regions, and white matter tracts that form the basis of Scherer's secondary structures. In contrast, the SDF-1alpha receptor, CXCR4, was highly expressed in invading glioma cells organized around neurons and blood vessels, in subpial regions, and along white matter tracts. Neuronal and endothelial cells exposed to vascular endothelial growth factor up-regulated the expression of SDF-1alpha. CXCR4-positive tumor cells migrated toward a SDF-1alpha gradient in vitro, whereas inhibition of CXCR4 expression decreased their migration. Similarly, inhibition of CXCR4 decreased levels of SDF-1alpha-induced phosphorylation of FAK, AKT, and ERK1/2, suggesting CXCR4 involvement in glioma invasion signaling. These studies offer one plausible molecular basis and explanation of the formation of Scherer's structures in glioma patients.