The helix-loop-helix protein ID1 localizes to centrosomes and rapidly induces abnormal centrosome numbers.

ID1 is a member of the inhibitor of DNA binding/differentiation (ID) family of dominant negative helix-loop-helix transcription factors. ID-proteins have been implicated in the control of differentiation and transcriptional modulation of various cell cycle regulators and high levels of ID1 expression are frequently detected in various cancer types. However, it is unclear whether ID1 is a marker of highly proliferative cancer cells or whether it directly contributes to the tumor phenotype. A detailed analysis of ID1-expressing human cells revealed that a fraction of ID1 localizes to centrosomes. Ectopic expression of ID1 in primary cells and tumor cell lines resulted in accumulation of cells with abnormal centrosome numbers. There was no evidence for centrosomal localization or induction of centrosome abnormalities by the other ID family members. Hence, ID1 may contribute to oncogenesis not only by inhibiting transcriptional activity of basic helix-loop-helix transcription factors and abrogate differentiation but also by subverting centrosome duplication.