Inhibitor of DNA-binding protein

Inhibitor of DNA-binding/differentiation proteins, also known as Id proteins comprise a family of proteins that heterodimerize with basic-helix-loop-helix (bHLH) transcription factors to inhibit DNA binding of bHLH proteins. Id proteins also contain the HLH-dimerization domain but lack the basic DNA-binding domain and thus negatively regulate bHLH transcription factors when they heterodimermize with bHLH proteins.

Function
ID proteins are key regulators of development where they function to prevent premature differentiation of stem cells. In contrast, inappropriate regulation of ID proteins in differentiated cells can contribute to tumorigenesis. Finally expression of ID proteins in neurons halts neuron axon growth and allows elongation of neurons.

Subtypes
Humans express four types of Id proteins (called ID1, ID2, ID3, and ID4).

A recent publication in Cancer Research (August 2010) has shown that ID1 can be used to mark Endothelial Progentior Cells which are critical to tumour growth and angiogenesis. This publication has demonstrated that targeting ID1 resulted in decreased tumour growth. Therefore, ID1 could be used to design a novel cancer therapy.