Data from Spatiotemporal Differences in CXCL12 Expression and Cyclic AMP Underlie the Unique Pattern of Optic Glioma Growth in Neurofibromatosis Type 1

Abstract

<div>Abstract<p>Astrocytoma (glioma) formation in neurofibromatosis type 1 (NF1) occurs preferentially along the optic pathway during the first decade of life. The molecular basis for this unique pattern of gliomagenesis is unknown. Previous studies in mouse <i>Nf1</i> optic glioma models suggest that this patterning results from cooperative effects of <i>Nf1</i> loss in glial cells and the action of factors derived from the surrounding <i>Nf1</i>+/− brain. Because CXCL12 is a stroma-derived growth factor for malignant brain tumors, we tested the hypothesis that CXCL12 functions in concert with <i>Nf1</i> loss to facilitate NF1-associated glioma growth. Whereas CXCL12 promoted cell death in wild-type astrocytes, it increased <i>Nf1</i>−/− astrocyte survival. This increase in <i>Nf1</i>−/− astrocyte survival in response to CXCL12 was due to sustained suppression of intracellular cyclic AMP (cAMP) levels. Moreover, the ability of CXCL12 to suppress cAMP and increase <i>Nf1</i>−/− astrocyte survival was a consequence of mitogen-activated protein/extracellular signal-regulated kinase kinase–dependent inhibition of CXCL12 receptor (CXCR4) desensitization. In support of an instructive role for CXCL12 in facilitating optic glioma growth, we also show that CXCL12 expression along the optic pathway is higher in infant children and young mice and is associated with low levels of cAMP. CXCL12 expression declines in multiple brain regions with increasing age, correlating with the age-dependent decline in glioma growth in children with NF1. Collectively, these studies provide a mechanism for the unique pattern of NF1-associated glioma growth. [Cancer Res 2007;67(18):8588–95]</p></div>