Promoter hypermethylation-mediated down-regulation of CXCL12 in human astrocytoma.

It has recently been demonstrated that CXCL12 is absent in colonic carcinoma, and hypermethylation of CXCL12 contributes to CXCL12/CXCR4 signaling in carcinoma metastasis. However, the role of CXCL12/CXCR4 axis, especially CXCL12, in the regulation of tumor invasiveness is largely still unknown. Using real-time quantitative RT-PCR assays, we observed that CXCR4 expression increased with increasing WHO grade in astrocytoma, suggesting that CXCR4 may be a marker of aggressive biological behavior of astrocytoma. Methylation of CXCL12 was detected in 34.2% (26/76) of astrocytomas by methylation-specific PCR. Epigenetic inactivation of CXCL12 was implicated mainly in low-grade astrocytomas, via DNA hypermethylation by DNMT1, -3A, and -3B; 21.1% (16/76) of the astrocytomas showed reduced or lack of CXCL12 expression, in line with epigenetic silencing of gene transcripts. However, it is interesting to note that 61.8% (47/76) of tumors, mainly high-grade astrocytomas, displayed elevated transcription of CXCL12. The expression levels of CXCL12 mRNA in glioblastomas (WHO grade IV) were significantly higher than in normal brain tissues. In summary, our data show that CXCL12 promoter hypermethylation is an early event in astrocytoma development. However, the high expressions of CXCR4 and CXCL12 in glioblastomas, the more invasive astrocytomas, suggest a different role of CXCL12/CXCR4 signaling axis in astrocytoma progression.