A novel differentiation factor for PC12 cells from culture supernatant of mouse hepatocyte cell line MLE-15A2

We have found a factor that induces neurite outgrowth of rat PC12 cells in the culture supernatant of the cell line MLE-15A2. This factor was designated as MDDF. The factor was sensitive to protease, dithiothreitol, and high-temperature treatments. The apparent molecular mass was 80 kDa on Superdex 200 gel filtration. No significant tyrosine phosphorylation was detected after MDDF stimulation in Western blotting analysis with anti-phosphotyrosine antibody, suggesting that the signal transduction may not be mediated by a tyrosine kinase cascade that is involved in signaling of most of the known factors. Activation of MAP kinase was very weak and was seen only 5 min after stimulation, suggesting that prolonged activation of MAP kinase was not required for neurite outgrowth induced by MDDF. Because the biochemical characteristics of MDDF are different from those of any known peptide factors that induce neurite outgrowth of PC12 cells, MDDF may be a novel differentiation factor for PC12 cells.