KDM5B and breast cancer: In this regard, the observation that the ratio between the two isoforms is significantly different between the luminal breast cancer MCF7 cell line (KDM5B-NTT around 40%) and the triple-negative/basal-like MDA-MB-231 (KDM5B-NTT around 57%) suggests a possible dominant-negative role of the inactive isoform in lowering PLU-1 activity by competing for genomic targets in the basal cell lines where high PLU-1 expression has been shown to inhibit optimal growth [23].