Overexpression of SPHK1 in the esophageal carcinoma EC9706-P4 subline with high invasive capacity. EC9706 cells were seeded onto Matrigel-coated transwells and allowed to invade into the lower chamber of the transwell, collected, expanded and then re-seeded onto another Matrigel-coated transwell. After four rounds of selection, the relatively stable, highly invasive subline, EC9706-P4, was established. (A) Transwell invasion analysis showed the invasive ability of EC9706-P4 was about 15-fold greater than the parent cell line EC9706 (P < 0.05) (B) The differential gene expression profiles of EC9706 and EC9706-P4 were analyzed by microarray, and expression of some genes were confirmed by QRT-PCR. Most of the dysregulated genes were previously associated with tumor invasion and metastasis. Notably, SPHK1 expression gradually increased through each round of selection from EC9706 to EC9706-P4.