The
Brn-3b transcription factor has been shown to be overexpressed in human
breast cancer cells and contributes toward cell growth regulation. Using micro-arrays, more than 50
cancer-related genes regulated by Brn-3b in human
breast cancer cells have been identified. For example, Brn-3b activates the cell cycle regulator CDK4 that provides a mechanism by which Brn-3b controls the growth of
breast cancer cells. Here, we show that Brn-3b regulates
plakoglobin (
gamma-catenin), a member of the
catenin family involved in cell-cell adhesion and signal transduction. Brn-3b expression inversely correlates with
plakoglobin expression at both
mRNA and
protein levels in
breast cancer cell lines and human breast biopsies. In contrast, no significant correlation was observed between Brn-3b expression and
beta-catenin, or between Brn-3b expression and
E-cadherin expression. Brn-3b represses the
plakoglobin promoter via a Brn-3 consensus binding site contained within the region -965 to -593 relative to the transcriptional start site. Both repression of the promoter and binding of Brn-3b are lost when this site is mutated. To our knowledge, this is the first time that a Brn-3b POU family
transcription factor has been shown to regulate a member of the
catenin family, which provides insight into the molecular mechanisms by which Brn-3b expression may favour
breast cancer progression and
tumor invasion.