Signaling Pathways Implicated in the Stimulation of β-Cell Proliferation by Extracellular Matrix

Abstract

Laminin-5-rich extracellular matrix derived from 804G cells (804G-ECM) induces spreading, improves glucose-stimulated insulin secretion, and increases survival and proliferation of rat pancreatic beta-cells. The aim of the study was to determine growth signaling pathways activated by ECM with a particular focus on Ca2+-dependent transcription factors. 804G-ECM increased rat β-cell proliferation and this stimulation was glucose- and Ca2+-dependent. NF-κB nuclear translocation as well as IkBα gene expression were also Ca2+-dependent. Inhibition of NF-κB almost completely blocked 804G-ECM-stimulated β-cell proliferation as did the soluble IL-1 receptor antagonist IL-1Ra. 804G-ECM-induced proliferation was also blocked by cyclosporin A and the VIVIT peptide suggesting involvement of NFAT/calcineurin. Use of selective inhibitors further implicated other pathways in this process. Inhibition of PI3 kinase and protein kinase A both prevented β-cell replication stimulated by 804G-ECM. Conversely, inhibition of MAPK, JNK, p38 and GSK3β increased β-cell proliferation on 804G-ECM. Our results suggest that Ca2+ entry which is necessary for increased β-cell proliferation on 804G-ECM is also involved in 804G-ECM induced NF-κB activity. It is proposed that increased cytosolic Ca2+ leads to activation of the transcription factors NFAT and NF-κB that in turn increase beta-cell proliferation. Activation of PI3 kinase by 804G-ECM also increases proliferation possibly by synergistic co-activation of NFAT via inhibition of GSK3β, while IL-1β may amplify the process by feed-forward activation of NF-κB. Conversely, inhibition of the MAPK pathway increased beta-cell proliferation indicating a counter-regulatory restraining role for this signaling pathway.