Cellular metastasis is the most detrimental step in carcinoma disease progression, yet the mechanisms that regulate this process are poorly understood. CXCL12 and its receptor CXCR4 are co-expressed in several tissues and cell types throughout the body and play essential roles in development. Disruption of either gene causes embryonic lethality due to similar defects. Post-natally, CXCL12 signaling has a wide range of effects on CXCR4-expressing cells, including the directed migration of leukocytes, lymphocytes and hematopoietic stem cells. Recently, this signaling axis has also been described as an important regulator of directed carcinoma cell metastasis. We show herein that while CXCR4 expression remains consistent, constitutive colonic epithelial expression of CXCL12 is silenced by DNA hypermethylation in primary colorectal carcinomas as well as colorectal carcinoma-derived cell lines. Inhibition of DNA methyltransferase (Dnmt) enzymes with 5-aza-2′-deoxycytidine or genetic ablation of both Dnmt1 and Dnmt3b prevented promoter methylation and restored CXCL12 expression. Re-expression of functional, endogenous CXCL12 in colorectal carcinoma cells dramatically reduced metastatic tumor formation in mice, as well as foci formation in soft agar. Decreased metastasis was correlated with increased caspase activity in cells re-expressing CXCL12. These data constitute the unique observation that silencing CXCL12 within colonic carcinoma cells greatly enhances their metastatic potential.
Bibliographical noteFunding Information:
We thank Dr Richard Komorowski (Froedtert Lutheran Memorial Hospital) and Dr Nita Salzman (Medical College of Wisconsin) for assisting in the analysis of primary carcinoma tissues under approval of the Medical College of Wisconsin Institutional Review Board. Portions of the immunohistochemical staining were comple ted in cooperation with the laboratory of Dr Martin Kagnoff (University of California, San Diego, USA). We appreciate the kind assistance of Dr Bert Vogelstein (John Hopkins University School of Medicine) for providing us with the Dnmt knockout cell lines. Support was provided by National Institutes of Health Grants DK062066 and DK002808, as well as a FIRST Award from the Crohn’s and Colitis Foundation of America and a grant from Medical College of Wisconsin Cancer Center.
- Epithelial cell
- Intestinal mucosa