Crlz1 activates transcription by mobilizing cytoplasmic CBFβ into the nucleus

Transcriptional function of a novel Crlz1 protein was examined by using the CBF site-containing IgJ enhancer, because it was originally cloned due to its ability to bind CBFβ, a subunit of CBF heterodimer, of which Runx is the other subunit. In a cotransfection experiment, Crlz1 was shown to increase the IgJ enhancer activity due to its CBF sites, as verified by both the absence of Crlz1 effect on the CBF-site mutated IgJ enhancer and the presence of transcriptional synergy between Crlz1 and CBFβ. Most significantly, the cytoplasmic CBFβ was shown to be mobilized into the nucleus when it was coexpressed with the nuclear Crlz1. This mobilized nuclear CBFβ could then heterodimerize with the nuclear Runx to bind to its target DNA site with a high affinity. Furthermore, in our coimmunoprecipitation and chromatin immunoprecipitation experiments, Crlz1 was found to be bound to the resulting CBF heterodimer in a form of ternary complex and to remain in that ternary complex even when CBF bound to its target DNA site such as IgJ enhancer.