Dual role of the tyrosine kinase GTK and the adaptor protein SHB in beta-cell growth: enhanced beta-cell replication after 60% pancreatectomy and increased sensitivity to streptozotocin

Abstract

Transgenic CBA mice expressing either the tyrosine kinase GTK (gut tyrosine kinase) or the adaptor protein SHB (Src homology 2 protein of beta-cells) under the control of the rat insulin promoter exhibited an increased beta-cell mass, but also elevated cytokine-induced islet cell death compared with control mice. To further investigate the importance of GTK and SHB for beta-cell death and proliferation, these mice were subjected to a 60% partial pancreatectomy (Px) or a sham-operation and beta-cell replication was determined by autoradiographic detection of [(3)H]thymidine incorporation into islet cells positively stained for insulin. The Px-operated control mice exhibited a moderate and insignificant increase in beta-cell replication 4 days after Px compared with the sham-operated mice (0.27+/-0.08% vs 0.08+/-0.02%). In contrast, the Px-induced beta-cell proliferation was significantly increased in both the GTK- and SHB-transgenic mice compared with the corresponding sham-treated animals (0.64+/-0.12% vs 0.11+/-0.04% and 0.44+/-0.11% vs 0.09+/-0.04% respectively). This effect was dependent on intracellular signal transduction pathways activated or enhanced by GTK and SHB overexpression, since the proliferation of acinar cells, located in the vicinity of the islets, was equal in the transgenic and control mice. GTK- and SHB-transgenic mice, treated with a sub-diabetogenic dose of the beta-cell toxin streptozotocin (STZ) on day 0 and subjected to a glucose tolerance test on day 3, exhibited an impaired glucose tolerance in comparison with the STZ-treated control mice. Pretreatment with STZ blunted the regenerative response to Px in the transgenic mice. Furthermore, the SHB-transgenic islets were significantly more damaged with respect to beta-cell loss, compared with the islets of the control mice. Previous and present data suggest a dual role of GTK and SHB for beta-cell growth: whereas these proteins increase the beta-cell mass and induce beta-cell proliferation after 60% Px, SHB and GTK also enhance beta-cell death under certain stressful conditions.