Separately, the importin system was found to mediate TERT nuclear import in MCF7 breast cancer cells; in particular, importin α binds TERT N-terminal nuclear localization signal (NLS) while its co-adaptor importin β1 binds Ran—a GTPase that shuttles its substrates in and out of the nucleus across the nuclear pore [28]. This evidence concerns the gene TERT and breast cancer.