A novel role for 14–3–3σ in regulating epithelial cell polarity

The loss of epithelial polarity is thought to play an important role during mammary tumor progression. Using a unique transgenic mouse model of ErbB2-induced mammary tumorigenesis, we demonstrated previously that amplification of ErbB2 is frequently accompanied by loss of the 14–3–3 σ gene. Here, we demonstrate that ectopic expression of 14–3–3σ results in restoration of epithelial polarity in ErbB2-transformed mammary tumor cells. We further demonstrate that targeted deletion of 14–3–3σ within primary mammary epithelial cells increases their proliferative capacity and adversely affects their ability to form polarized structures. Finally, we show that 14–3–3σ can specifically form complexes with Par3, a protein that is essential for the maintenance of a polarized epithelial state. Taken together, these observations suggest that 14–3–3σ plays a critical role in retaining epithelial polarity.