Upregulation of B-cell translocation gene 2 by epigallocatechin-3-gallate via p38 and ERK signaling blocks cell proliferation in human oral squamous cell carcinoma cells

Oral squamous cell carcinoma (OSCC) is a well-known malignancy that accounts for the majority of oral cancers. B-cell translocation gene 2 (BTG2) is an important regulator of cell cycle dynamics in cancer cells. However, the role of BTG2 in OSCC cells and the influences of epigallocatechin-3-gallate (EGCG) on BTG2 gene expressions have not been well evaluated. The objectives of this study were to examine the effect of EGCG-induced BTG2 expression and the potential signal pathways involved. The 3H-thymidine incorporation and Western-blot assays revealed cell proliferation was attenuated by EGCG via upregulation of BTG2 expression causing cell cycle G1 phase arrest in OSCC cells. BTG2 overexpression decreased tumor cell growth, while BTG2 knockdown illuminated the opposite effect in xenograft animal studies. Overexpressed BTG2 arrested the cell cycle at the G1 phase and downregulated protein expressions of cyclin A, cyclin D, and cyclin E. Western-blot assays indicated that EGCG induced phosphorylation of p38, JNK, and ERK. However, pretreatments with selective mitogen-activated protein kinase (MAPK) inhibitors, SB203580 (p38 inhibitor) and PD0325901 (ERK1/2 inhibitor), significantly suppressed the activation of EGCG on BTG2 expression. Our results indicate that EGCG attenuates cell proliferation of OSCC cells by upregulating BTG2 expression via p38 and ERK pathways.