FHL1 interacts with oestrogen receptors and regulates breast cancer cell growth

Four and a half LIM protein 1 (FHL1) belongs to the Lin-1, Isl-1 and Mec-3 (LIM)-only protein family and plays important roles in muscle growth and carcinogenesis. However, the biological function of FHL1 remains largely unknown. Here, we show that FHL1 physically and functionally interacted with oestrogen receptors (ERs), which are involved in breast cancer development and progression. FHL1 bound specifically to the activation function-1 domain of ER. Physical interaction of FHL1 and ER is required for FHL1 repression of oestrogen-responsive gene transcription. FHL1 affected recruitment of ER to an oestrogen-responsive promoter and ER binding to an oestrogen-responsive element. Overexpression of FHL1 in breast cancer cells decreased expression of oestrogen-responsive proteins, whereas knockdown of endogenous FHL1 with FHL1 small interfering RNA increased the expression of these proteins. Further analysis of 46 breast cancer samples showed that FHL1 expression negatively associated with oestrogen-responsive gene expression in breast cancer cells. FHL1 inhibited anchorage-dependent and -independent breast cancer cell growth. These results suggest that FHL1 may play an important role in ER signalling as well as breast cancer cell growth regulation.