Alx4 binding to LEF-1 regulates N-CAM promoter activity

During murine embryogenesis, expression of the paired-like homeodomain protein Alx4 is restricted to tissues whose development depends on the expression of lymphoid enhancer factor-1 (LEF-1). Given the defects seen in hair follicle development in both LEF-1 and Alx4 knockout and mutant animals and the overlapping expression patterns, we predicted that LEF-1 and Alx4 might form physical complexes. We demonstrate here the interaction between LEF-1 and Alx4. This interaction is mediated through a specific proline-rich domain in the N-terminal region of Alx4 and requires the DNA-binding domain (HMG-box) of LEF-1. We also demonstrate that LEF-1 and Alx4 can bind simultaneously to adjacent sites on the neural cell adhesion molecule (N-CAM) promoter and that this binding alters N-CAM promoter activity. Furthermore, when expressed in primary mammary stromal cells, Alx4 decreases the expression of endogenous N-CAM protein. These results reveal a potential mechanism that gives rise to mesenchymal-specific activities of LEF-1.