PTN and central nervous system cancer: In contrast to other cell types, such as glioma U373 cells, 3T3-L1 preadipocytes, fetal alveolar epithelial type II cells and cultured embryonic mouse (E14.5) neurons3, PTN stimulation of HUVEC had no effect on β-catenin tyrosine phosphorylation or cell membrane localization, suggesting that β-catenin is not implicated in the PTN pathway that leads to CDK5 activation.