TGF-β1 induces amoeboid-to-mesenchymal transition of CD44 oral squamous cell carcinoma cells via miR-422a downregulation through ERK activation and Cofilin-1 phosphorylation.

Background: The objective of this study was to clarify the molecular mechanism of amoeboid-to-mesenchymal transition (AMT) of CD44 oral squamous cell carcinoma (OSCC) cells.

Methods: Morphology and expression of mesenchymal genes were investigated in CD44 OSCC cells (CD44 OM-1 cells) cultured on laminin-coated soft silicone gel. Additionally, microarray analysis was performed to investigate microRNA (miRNA) expression inhibited by transforming growth factor-β1 (TGF-β1) in CD44 OM-1 cells.

Results: When CD44 OM-1 cells were cultured on 2.0-kPa laminin-coated silicone gel, the cells exhibited an amoeboid-like round morphology. Cofilin-1 expression was found in the nucleus and cytoplasm of amoeboid-like CD44 OM-1 cells. The invasive capacity was significantly reduced after Cofilin-1 knockdown. Additionally, Cofilin-1 knockdown cells had an irregularly extended shape. Phosphorylated Cofilin-1 was significantly upregulated by TGF-β1. Additionally, TGF-β1 enhanced N-cadherin and Snail mRNA expression and induced a spindle-shaped morphology. ERK1/2 phosphorylation was induced by TGF-β1. Microarray analysis revealed that miR-422a exhibited the greatest downregulation (fold change: 0.22) in the presence of TGF-β1. Importantly, TGF-β1-inhibited miR-422a expression was recovered by the ERK inhibitor or ERK1/2 knockdown. Additionally, miR-422a inhibitor-transfected CD44 OM-1 cells exhibited high N-cadherin and Snail mRNA expression. Furthermore, Cofilin-1 knockdown and miR-422a inhibition induced a spindle cell morphology.

Conclusion: Cofilin-1 is involved in the invasive ability of CD44 OSCC cells. TGF-β1 contributes to AMT by downregulation of miR-422a via ERK activation and Cofilin-1 phosphorylation. Our findings suggest that miR-422a and Cofilin-1 play major roles in the maintenance of amoeboid-like CD44 cells.