Overexpression of USF increases TGF-beta1 protein levels, but G1 phase arrest was not induced in FRTL-5 cells.

Transforming growth factor-beta1 (TGF-beta1) is a potent inhibitor of cellular growth and proliferation by G1 phase arrest or apoptosis. We investigated the association of TGF-beta1 with the anti-proliferative effect of upstream stimulatory factor (USF) in Fischer rat thyroid cell line (FRTL-5) cells. [methyl-(3)H] thymidine uptake was measured after treatment of FRTL-5 cells with TGF-beta1 to identify its anti-proliferative effect.

USF inhibits cell proliferation through delay in G2/M phase in FRTL-5 cells.

Upstream stimulatory factor (USF) has a negative effect on the cell proliferation in some cell types. However, its effect on thyrocytes is not clear. Therefore, we investigated the effects of USF on the proliferation and function of thyroid follicular cells.