Bach1 as a regulator of mitosis, beyond its transcriptional function

Bach1 is a transcriptional repressor which modulates several critical transcriptional responses, such as the expression of the heme oxygenase-1 (HO-1) gene in response to oxidative stress. In our recent study, we found that Bach1 possesses a novel role in mitotic chromosome alignment during metaphase. Upon BACH1 depletion in HeLa cells, mitotic chromosomes become unstable. This defect was efficiently rescued by expressing Bach1 fragments that lack the DNA binding domain, indicating that its function in mitosis involves a transcription-independent mechanism. The nuclear export signal (NES/CLS) of Bach1 is required for the mitotic function. Bach1 is excluded from the mitotic chromosomes depending on its NES/CLS and the nuclear exporter Crm1. Our findings suggest that Bach1 might mediate the regulation of mitotic chromosomes under conditions of cellular stress.