Fibulins (FBLNs), a family of
extracellular matrix proteins, have recently been shown to act as
tumor suppressors or activators in different
cancers, and the underlying molecular mechanisms of their action in
cancer remain unclear. We have previously shown that the expression of FBLN3 is suppressed by promoter hypermethylation and is associated with invasiveness in aggressive
non-small cell lung cancer. In this study, we evaluated the roles and signaling mechanism of FBLN3 in
lung cancer stem cells (CSCs). Forced expression of FBLN3 suppressed invasion and migration of
lung adenocarcinoma cells and decreased the expression of epithelial-to-mesenchymal transition (EMT) activators, including
N-cadherin and Snail. Stemness activities of
lung adenocarcinoma cells were also suppressed by FBLN3 as indicated by a decrease in spheroid formation and the levels of stemness markers such as Sox2 and β-
catenin. These effects of FBLN3 were mediated by the
glycogen synthase kinase-3β, GSK3β/β-
catenin pathway, and the upstream regulators of GSK3β, including
phosphoinositide 3-kinase (PI3K)/AKT and
insulin-like growth factor-1 receptor (IGF1R), were inactivated by FBLN3. Moreover, IGF1R was shown to be a direct target of FBLN3, which competitively inhibited
insulin-like growth factor (IGF) action. To confirm the effect of FBLN3 on lung CSCs,
aldehyde dehydrogenase-positive (ALDH+) A549 lung CSCs were sorted and treated with recombinant FBLN3
protein. FBLN3 clearly suppressed EMT, stemness activity and the over-activated IGF1R/PI3K/AKT/GSK3β pathway of the ALDH+ CSC subpopulation. In addition, injection of recombinant FBLN3
protein around subcutaneous xenografts established with ALDH+ CSCs in athymic nude mice significantly suppressed
tumor growth and progression. Overall, our results show that FBLN3 suppresses both EMT and self-renewal of the lung CSCs by modulating the IGF1R/PI3K/AKT/GSK3β pathway and that FBLN3 would be useful as an alternative CSC
therapy.