Inositol polyphosphate-4-phosphatase type II plays critical roles in the modulation of cadherin-mediated adhesion dynamics of pancreatic ductal adenocarcinomas

The inositol polyphosphate-4-phosphatase type II (INPP4B) has been mostly proposed to act as a tumor suppressor whose expression is frequently dysregulated in numerous human cancers. To date, little is unveiled about whether and how INPP4B will exert its tumor suppressive function on the turnover of cadherin-based cell-cell adhesion system in pancreatic ductal adenocarcinomas (PDACs) in vitro. Here we provide the evidence that INPP4B manipulates cadherin switch in certain PDAC cell lines through a phosphorylated AKT-inactivation manner. The knockdown of INPP4B in AsPC-1 results in a more invasive phenotype, and overexpression of it in PANC-1 leads to partial reversion of mesenchymal status and impediment of in vitro invasion but not migration. More importantly, E-cadherin (Ecad) is enriched in the early and sorting endosomes containing INPP4B by which its recycling rather than degradation is enabled. Immunohistochemical analysis of 39 operatively resected PDAC specimens reveals it is poorly differentiated, non-cohesive ones in which the INPP4B and Ecad are partially or completely compromised in expression. We therefore identify INPP4B as an tumor suppressor in PDAC which attenuates AKT activation and participates in preservation of Ecad in endocytic pool and cellular membrane.