Lysyl oxidase like 4, a novel target gene of TGF-β1 signaling, can negatively regulate TGF-β1-induced cell motility in PLC/PRF/5 hepatoma cells

Transforming growth factor-β1 (TGF-β1) is a multi-functional cytokine involved in the regulation of cell proliferation, differentiation and extracellular matrix formation. In search for novel genes mediating the TGF-β1 function at downstream signaling, we performed a cDNA microarray analysis and identified 60 genes whose expression is regulated by TGF-β1 in the liver cancer cell line PLC/PRF/5. Among them, we report here lysyl oxidase like 4 (LOXL4) as a novel target of TGF-β1 signaling, and provide experimental evidence for its expression regulation and function. LOXL4 was found to be the only member of LOX family whose expression is induced by TGF-β1 in hepatoma cells. Deletion mapping of the LOXL4 promoter indicated that the TGF-β1 regulation of LOXL4 expression is mediated through the binding of AP1 transcription factor to a conserved region of the promoter. This was confirmed by the chromatin immunoprecipitation assay that captured c-Fos-bound chromatin from TGF-β1-treated cells. Forced expression of LOXL4 in PLC/PRF/5 cells resulted in inhibition of cell motility through Matrigel in the presence of TGF-β1 treatment. In parallel, LOXL4 suppressed the expression of laminins and α3 integrin and the activity of MMP2. These results suggest that LOXL4 may function as a negative feedback regulator of TGF-β1 in cell invasion by inhibiting the metabolism of extracellular matrix (ECM) components.