p67 isoform of mouse disabled 2 protein acts as a transcriptional activator during the differentiation of F9 cells.

The mouse disabled 2 (mDab2) gene is a mouse homologue of the Drosophila disabled gene and is alternatively spliced to form two isoforms, p96 and p67. Although p96 has been known to regulate the Ras-Sos G-protein signal transduction pathway by interacting with Grb2, little is known about the biological function of p67. Recent studies have shown that the expression of mDab2 is markedly up-regulated during the retinoic acid (RA)-induced differentiation of F9 cells, suggesting another role for mDab2 in cell differentiation [Cho, Lee and Park (1999) Mol. Cells 9, 179-184). In the present study, we first elucidated the biological function of p67 isoform of mDab2 and identified its binding partner. Unlike p96, p67 largely resides in RA-treated F9 cell nuclei. In this system, p67 interacts with mouse androgen-receptor interacting protein 3, termed the mDab2 interacting protein, which acts as a transcriptional co-regulator. By using a fusion protein with a heterologous DNA-binding domain (GAL4), we showed that p67 had an intrinsic transcriptional activation function. These results suggest that mDab2 p67 may function as a transcriptional co-factor for certain complexes of transcriptional regulatory elements involved in the RA-induced differentiation of F9 cells.