FHL1 inhibits the growth of tongue squamous cell carcinoma cells via G1/S cell cycle arrest.

Four and a half LIM protein 1 (FHL1) has been characterized as a tumor suppressor in various types of tumor. However, the biological function and underlying mechanism of FHL1 in tongue squamous cell carcinoma (TSCC) remain to be elucidated. The present study demonstrated that FHL1 inhibits anchorage­dependent and ­independent growth of TSCC cells in vitro and tumor growth in nude mice, as determined by cell proliferation and soft agar assays. Knockdown of FHL1 with FHL1 small interfering RNA (siRNA) promoted tumor growth in nude mice. Mechanistically, flow cytometric analysis showed that knockdown of FHL1 promoted G1/S cell cycle progression. Furthermore, expression of cell cycle­associated regulators, cyclin D and cyclin E, were detected by western blotting and reverse transcription­quantitative polymerase chain reaction. Cyclin D and cyclin E were markedly elevated at both the protein and mRNA level in the FHL1 siRNA­transfected cells. These results suggested that FHL1 has a tumor suppressive role in TSCC and that FHL1 may be a useful target for TSCC gene therapy.