The Interaction between Laminin-332 and alpha 3 beta 1 Integrin Determines Differentiation and Maintenance of CAFs, and Supports Invasion of Pancreatic Duct Adenocarcinoma Cells

Ranking among the most lethal tumour entities, pancreatic duct adenocarcinoma cells invade neighbouring tissue resulting in high incidence of metastasis. They are supported by tumour stroma fibroblasts which have undergone differentiation into cancer-associated fibroblasts (CAFs). Stiffness of cell substratum, cytokines, such as transforming growth factor-beta (TGF-beta), and stromal matrix proteins, such as laminin-332, are factors which promote CAF differentiation. In a spheroid culture system, differentiation of CAFs was analysed for laminin-332 production, laminin-binding integrin repertoire, adhesion and migration behaviour, and, in heterospheroids, for their interplay with the pancreatic duct adenocarcinoma AsPC-I cells. Our data reveal that CAFs produce laminin-332 thus contributing to its ectopic deposition within the tumour stroma. Moreover, CAF differentiation correlates with an increased expression of alpha 3 beta 1 integrin, the principal laminin-332-receptor. Beyond its role as novel CAF marker protein, integrin alpha 3 beta 1 crucially determines differentiation and maintenance of the CAF phenotype, as knock-out of the integrin alpha 3 subunit reversed the CAF differentiated state. AsPC-I cells co-cultured in heterospheroids with integrin alpha 3-deficient CAFs invaded less than from heterospheroids with wild-type CAFs. This study highlights the role of integrin alpha 3 beta 1 integrin-laminin-332 interaction of CAFs which promotes and sustains differentiation of CAFs and promotes carcinoma invasion.