Characterization of Laminin 5B and NH2-terminal Proteolytic Fragment of Its α3B Chain PROMOTION OF CELLULAR ADHESION, MIGRATION, AND PROLIFERATION

Abstract Various laminin isoforms have specific biological functions depending on their structures. Laminin 5A, which consists of the three truncated chains α3A, β3, and γ2, is known to have strong activity to promote cell adhesion and migration, whereas a laminin 5 variant consisting of a full-sized α3 chain (α3Β) and the β3 and γ2 chains, laminin 5B, has not been characterized yet. In the present study, we for the first time cloned a full-length human laminin α3B cDNA and isolated the human laminin 5B protein. The molecular size of the mature α3B chain (335 kDa) was approximately twice as large as the mature α3A chain in laminin 5A. Laminin 5B had significantly higher cell adhesion and cell migration activities than laminin 5A. In addition, laminin 5B potently stimulated cell proliferation when added into the culture medium directly. Furthermore, we found that the α3B chain undergoes proteolytic cleavage releasing a 190-kDa NH2-terminal fragment. The 190-kDa fragment had activities to promote cellular adhesion, migration, and proliferation through its interaction with integrin α3β1. These activities of the NH2-terminal structure of the α3B chain seem to contribute to the prominent biological activities and the physiological functions of laminin 5B.