ID proteins as targets in cancer and tools in neurobiology

In eukaryotic organisms, ID proteins are key regulators of development when they function to preserve the stem cell state and prevent lineage determination. By fueling several key features of tumor progression (deregulated proliferation, invasiveness, angiogenesis and metastasis), ID proteins contribute to multiple steps of tumorigenesis. Through oncogenic processes that lead to their aberrant activation in tumors, ID proteins transfer the phenotypic traits of embryonic stem cells to cancer cells. However, ID proteins have recently emerged as highly specialized factors in post-mitotic neurons. The elevated expression of ID proteins arrests neurons in the axon growth mode and prevents cessation of axonal elongation. Here, we discuss how unique properties of ID proteins in cancer cells and neurons pave the way to unexpected therapeutic opportunities.