PTTG overexpression promotes lymph node metastasis in human esophageal squamous cell carcinoma

Human pituitary tumor transforming gene (PTTG) overexpression correlates with metastasis in multiple tumors, and yet its molecular mechanisms of action remain elusive. We detected PTTG overexpression in 66% (111 of 169) of primary esophageal squamous cell carcinoma (ESCC) tumor tissues by in situ hybridization. PTTG overexpression correlated with lymph node metastasis (P < 0.05). Ectopic PTTG overexpression in a representative ESCC cell line, EC9706, increased in vitro cell migration and invasion and promoted in vivo lymph node metastasis. Suppressing PTTG expression by siRNA decreased cell motility in both PTTG-HA/EC9706 and KYSE150 cells. By using mass spectrometric analysis, we identified that PTTG up-regulated S100A4 and galectin-1 secretion and down-regulated tissue inhibitor of metalloproteinase-2 secretion to the culture media. PTTG induced S100A4 and galectin-1 mRNA and protein expression as assessed by Western blot and reverse transcription-PCR. Attenuating galectin-1 expression by siRNA constrained PTTG-HA/EC9706 cell motility (P < 0.05). PTTG activated E-box transcription and induced c-Myc protein expression in EC9706 cells, which in turn may act on an E-box motif within the galectin-1 promoter. Chromatin immunoprecipitation assays further confirmed specific c-Myc binding to galectin-1 promoter. PTTG-induced galectin-1 transactivation and expression were mediated by c-Myc, and both inductions were suppressed by c-Myc RNAi cotranfection. These findings elucidate the molecular mechanisms of PTTG overexpression in promoting tumor metastasis, whereby up-regulated PTTG modulates expression and secretion of metastasis-related factors to facilitate cell motility