Members of helix-loop-helix (HLH) protein family of Id (inhibitor of differentiation) play important roles in regulation of differentiation and cell proliferation. Id proteins dimerize with basic helix-loop-helix (bHLH) transcription factor and function as negative regulators in differentiation. The negative roles of Id proteins have been well demonstrated in muscle development and lymphopoiesis. Id proteins have been also known as the positive regulators of cell proliferation In this study, we investigated whether Id proteins could inhibit neuronal differentiation. We used F11 neuroblastoma cells, which could be induced to grow neurites in the presence of cAMP. We first isolated cDNAs of Id by yeast two-hybrid system using the bHLH domain of E47, a ubiquitous bHLH partner as a bait. When expressed in COS cells, these Id proteins were found in the cytosolic and nuclear compartments. Overex-pression of Id proteins reduced neurite outgrowth in the presence of cAMP in F11 cells. The results suggest that Id protein may interact with endogenous bHLH factors and antagonize their neurogenic effects in F11 neurobalstoma cells. The results also suggest that F11 cells might be a useful system for the study of neurogenic transcription factor.

Keywords: Id, bHLH, F11, cAMP, neurite outgrowth