Conditional expression of hepatocyte nuclear factor-1β, the maturity-onset diabetes of the young-5 gene product, influences the viability and functional competence of pancreatic β-cells

Abstract

Mutations in the gene encoding hepatocyte nuclear factor (HNF)1b result in maturity-onset diabetes of the young-(MODY)5, by impairing insulin secretory responses and, possibly, by reducing b-cell mass. The functional role of HNF1b in normal b-cells is poorly understood; therefore, in the present study, wild-type (WT) HNF1b, or one of two naturally occurring MODY5 mutations (an activating mutation, P328L329del, or a dominant-negative form, A263insGG) were conditionally expressed in the pancreatic b-cell line, insulin-1 (INS-1), and the functional consequences examined. Surprisingly, overexpression of the dominant-negative mutant did not modify any of the functional properties of the cells studied (including insulin secretion, cell growth and viability). By contrast, expression of WT HNF1b was associated with a time-and dose-dependent inhibition of INS-1 cell proliferation and a marked increase in apoptosis. Induction of WT HNF1b also inhibited the insulin secretory response to nutrient stimuli, membrane depolarisation or activation of protein kinases A and C and this correlated with a significant decrease in pancrease-duodenum homeobox-1 protein levels. The attenuation of insulin secretion was, however, dissociated from the inhibition of proliferation and loss of viability, since expression of the P328L329del mutant led to a reduced rate of cell proliferation, but failed to induce apoptosis or to alter insulin secretion. Taken together, the present results suggest that mature rodent b-cells are sensitive to increased expression of WT HNF1b and they imply that the levels of this protein are tightly regulated to maintain secretory competence and cell viability.

The protein tyrosine phosphatase-BL, modulates pancreatic β-cell proliferation by interaction with the Wnt signalling pathway

“…This was confirmed at the protein level by western blotting (Welters et al 2006); thus PTP-BL has been established as an HNF1b-sensitive gene product in INS-1 cells.…”

“…Thus, identification of the proteins that are mutated in patients with MODY can provide important insights into the functional control of b-cell integrity. In this context, we have recently demonstrated that increased expression of the MODY5 gene product, HNF1b, leads to enhanced rates of apoptosis, altered regulation of the cell cycle and inhibition of stimulated insulin secretion in pancreatic b-cells, suggesting that control of HNF1b expression may be important for the regulation of b-cell viability and function (Welters et al 2006).…”

“…In view of the evidence that expression of PTP-BL is increased in b-cells having elevated levels of HNF1b, and that this correlates with altered proliferation under these conditions (Welters et al 2006), the present study has investigated the role of PTP-BL in mediating these changes. To achieve this, a b-cell line conditionally expressing PTP-BL under the control of a tetracycline-regulated promoter was generated and the effects of altered expression of PTP-BL studied.…”

Simultaneous determination of cell aging and ATP release from erythrocytes and its implications in type 2 diabetes

“…[1][2][3][4] A vast amount of research involving diabetes and complications is focused on areas such as insulin secretion and resistance, pancreatic beta cells, and maintenance of blood glucose levels. 5,6 of this weakened antioxidant defense, the RBCs of these individuals are more prone to oxidant insult and are believed to be less deformable in comparison to RBCs obtained from healthy individuals. Indeed, it has been reported that the RBCs from people with type 2 diabetes are less deformable than those RBCs obtained from healthy controls.…”

Structural Basis of Disease-Causing Mutations in Hepatocyte Nuclear Factor 1β,

“…Recently, HNF1β has also been associated with ovarian clear cell carcinoma (25,26), and mutations in this protein are also responsible for neonatal cholestatic jaundice (27). Thus, in addition to its effect on pancreatic β-cells (5,28,29), HNF1β appears to be involved in normal functioning of many other organs (10,11).…”