Developmental expression profile of the CXCL12gamma isoform: insights into its tissue-specific role

Natural nitration of CXCL12 reduces its signaling capacity and chemotactic activity in vitro and abrogates intra-articular lymphocyte recruitment in vivo

The chemokine CXCL12/stromal cell-derived factor-1 is important for leukocyte migration to lymphoid organs and inflamed tissues and stimulates tumor development. In vitro, CXCL12 activity through CXCR4 is abolished by proteolytic processing. However, limited information is available on in vivo effects of posttranslationally modified CXCL12. Natural CXCL12 was purified from the coculture supernatant of stromal cells stimulated with leukocytes and inflammatory agents. In this conditioned medium, CXCL12 with a nitration on Tyr⁷, designated [3-NT⁷]CXCL12, was discovered via Edman degradation. CXCL12 and [3-NT⁷]CXCL12 were chemically synthesized to evaluate the biological effects of this modification. [3-NT⁷]CXCL12 recruited β-arrestin 2 and phosphorylated the Akt kinase similar to CXCL12 in receptor-transfected cells. Also the affinity of CXCL12 and [3-NT⁷]CXCL12 for glycosaminoglycans, the G protein-coupled chemokine receptor CXCR4 and the atypical chemokine receptor ACKR3 were comparable. However, [3-NT⁷]CXCL12 showed a reduced ability to enhance intracellular calcium concentrations, to generate inositol triphosphate, to phosphorylate ERK1/2 and to induce monocyte and lymphocyte chemotaxis in vitro. Moreover, nitrated CXCL12 failed to induce in vivo extravasation of lymphocytes to the joint. In summary, nitration on Tyr⁷ under inflammatory conditions is a novel natural posttranslational regulatory mechanism of CXCL12 which may downregulate the CXCR4-mediated inflammatory and tumor-promoting activities of CXCL12.

Heparan sulfate differentially controls CXCL12α- and CXCL12γ-mediated cell migration through differential presentation to their receptor CXCR4

Chemokines stimulate signals in cells by binding to G protein (heterotrimeric guanine nucleotide-binding protein)-coupled receptors. These chemoattractant cytokines also interact with heparan sulfate (HS), which provides positional information within tissues in the form of haptotactic gradients along which cells can migrate directionally. To investigate the mechanism by which HS modulates chemokine functions, we used the CXC chemokine CXCL12, which exists in different isoforms that all signal through CXCR4 but have distinct HS-binding domains. In experiments with both cell-associated and solubilized CXCR4, we found that although CXCL12γ bound to CXCR4 with a higher affinity than did CXCL12α, CXCL12γ displayed reduced signaling and chemotactic activities. These properties were caused by the specific carboxyl-terminal region of CXCL12γ, which, by interacting with CXCR4 sulfotyrosines, mediated high-affinity, but nonproductive, binding to CXCR4. HS prevented CXCL12γ from interacting with the CXCR4 sulfotyrosines, thereby functionally presenting the chemokine to its receptor such that its activity was similar to that of CXCL12α. HS had no effects on the binding of CXCL12α to CXCR4 or its biological activity, suggesting that this polysaccharide controls CXCL12 in an isoform-specific manner. These data suggest that the HS-dependent regulation of chemokine functions extends beyond the simple process of immobilization and directly modulates receptor ligation and activation.

Ethanol diverts early neuronal differentiation trajectory of embryonic stem cells by disrupting the balance of lineage specifiers

Background

Ethanol is a toxin responsible for the neurodevelopmental deficits of Fetal Alcohol Spectrum Disorders (FASD). Recent evidence suggests that ethanol modulates the protein expression of lineage specifier transcription factors Oct4 (Pou5f1) and Sox2 in early stages of mouse embryonic stem (ES) cell differentiation. We hypothesized that ethanol induced an imbalance in the expression of Oct4 and Sox2 in early differentiation, that dysregulated the expression of associated and target genes and signaling molecules and diverted cells from neuroectodermal (NE) formation.

Methodology/Principal Findings

We showed modulation by ethanol of 33 genes during ES cell differentiation, using high throughput microfluidic dynamic array chips measuring 2,304 real time quantitative PCR assays. Based on the overall gene expression dynamics, ethanol drove cells along a differentiation trajectory away from NE fate. These ethanol-induced gene expression changes were observed as early as within 2 days of differentiation, and were independent of cell proliferation or apoptosis. Gene expression changes were correlated with fewer βIII-tubulin positive cells of an immature neural progenitor phenotype, as well as a disrupted actin cytoskeleton were observed. Moreover, Tuba1a and Gapdh housekeeping genes were modulated by ethanol during differentiation and were replaced by a set of ribosomal genes with stable expression.

Conclusions/Significance

These findings provided an ethanol-response gene signature and pointed to the transcriptional dynamics underlying lineage imbalance that may be relevant to FASD phenotype.

CXCL12-γ expression is inhibited in neuroinflammation

CXCL12 plays a protective role in CNS autoimmunity. Expression of CXCL12-γ, which has distinct structural and functional properties than the other isoforms of CXCL12, was determined in spinal cords of rats immunized to develop experimental autoimmune encephalomyelitis (EAE). CNS expression of CXCL12-γ was markedly lower in EAE-prone Dark Agouti rats than in EAE-resistant Albino Oxford rats, both in spinal cord homogenates and micro-blood vessels isolated from spinal cords. Inhibition of nitric oxide (NO) synthesis in DA rats upregulated, while donation of NO in AO rats downregulated CNS expression of CXCL12-γ. NO inhibited CXCL12-γ expression in astrocytes in vitro. A splice variant of CXCL12-γ which migrates into nucleolus was not detected in spinal cord or astrocytes. Thus, CXCL12-γ is expressed in the CNS after EAE induction, but its expression is markedly suppressed in spinal cord affected with full blown inflammation. NO is an important regulator of CXCL12-γ expression in neuroinflammation.