Prolactin/Jak2 directs apical/basal polarization and luminal linage maturation of mammary epithelial cells through regulation of the Erk1/2 pathway.

Tissue development/remodeling requires modulations in both cellular architecture and phenotype. Aberration in these processes leads to tumorigenesis. During the pregnancy/lactation cycle the mammary epithelial cells undergo complex morphological and phenotypic programs resulting in the acquisition of apical/basal (A/B) polarization and cellular maturation necessary for proper lactation. Still the hormonal regulations and cellular mechanisms controlling these events are not entirely elucidated. Here we show that prolactin (PRL)/Jak2 pathway in mammary epithelial cells uniquely signals to establish A/B polarity as determined by the apical localization of the tight junction protein zona occludens 1 (ZO-1) and the basal/lateral localization of E-cadherin, and the apical trafficking of lipid droplets. As well, our results indicate that this pathway regulates mammary stem cell hierarchy by inducing the differentiation of luminal progenitor (EpCAMhi/CD49fhi) cells to mature luminal (EpCAMhi/CD49flow) cells. Moreover, our data indicate that PRL/Jak2 coordinates both of these cellular events through limiting the mitogen activated protein kinase (Erk1/2) pathway. Together our findings define a novel unifying mechanism coupling mammary epithelial cell A/B polarization and terminal differentiation.

In vitro and in vivo characterization and strain safety of Lactobacillus reuteri NCIMB 30253 for probiotic applications.

Lactobacillus reuteri NCIMB 30253 was shown to have potential as a probiotic by reducing the proinflammatory chemokine interleukin-8. Moreover, this strain was evaluated, by in vitro and in vivo techniques, for its safety for human consumption. The identity of the strain was investigated by metabolic profiling and 16S rRNA gene sequencing, and in vitro safety evaluations were performed by molecular and metabolic techniques. Genetic analysis was confirmed by assessing the minimum inhibitory concentration to a panel of antibiotics, showing that the strain was susceptible to 8 antibiotics tested. The ability of the strain to produce potentially harmful by-products and antimicrobial compounds was evaluated, showing that the strain does not produce biogenic amines and does not show bacteriocin activity or reuterin production. A 28-day repeated oral dose study was conducted in normal Sprague-Dawley rats to support the in vivo strain safety. Oral administration of the strain resulted in no changes in general condition and no clinically significant changes to biochemical and haematological markers of safety relative to vehicle control treated animals. This comprehensive assessment of safety of L. reuteri NCIMB 30253 supports the safety of the strain for use as a probiotic.

Tyrosine phosphorylation of Grb2: role in prolactin/epidermal growth factor cross talk in mammary epithelial cell growth and differentiation.

Characterizing mechanisms regulating mammary cell growth and differentiation is vital, as they may contribute to breast carcinogenesis. Here, we examine a cross talk mechanism(s) downstream of prolactin (PRL), a primary differentiation hormone, and epidermal growth factor (EGF), an important proliferative factor, in mammary epithelial cell growth and differentiation. Our data indicate that EGF exerts inhibitory effects on PRL-induced cellular differentiation by interfering with Stat5a-mediated gene expression independent of the PRL-proximal signaling cascade. Additionally, our data show that PRL is a potent inhibitor of EGF-induced cell proliferation. We identify tyrosine phosphorylation of the growth factor receptor-bound protein 2 (Grb2) as a critical mechanism by which PRL antagonizes EGF-induced cell proliferation by attenuating the activation of the Ras/mitogen-activated protein kinase (MAPK) pathway. Together, our results define a novel negative cross-regulation between PRL and EGF involving the Jak2/Stat5a and Ras/MAPK pathways through tyrosine phosphorylation of Grb2.