Rapamycin Inhibits Growth Factor-Induced Cell Cycle Regulation in Pancreatic β Cells

Abstract

A progressive decline in islet function is a major obstacle to the success of islet transplantation. The cause of this decline in islet function is unclear, but immunosuppressive agents may contribute. Insulin-like growth factor-I (IGF-I) and betacellulin are important for islet cell survival and/or proliferation. In the present study, we performed studies in INS-1 cells and murine islets to define the effect of IGF-I and betacellulin on progression of islet cells through the cell cycle and the impact of immunosuppressive agents. Treatment of INS-1 cells for 24 hrs with 20 ng/ml betacellulin or 50 ng/ml IGF-I increased cells in S phase by ~2-fold. Treatment of INS-1 cells with IGF-I or betacellulin also increased cyclin D1 expression and nuclear exclusion of the cyclin-dependent kinase inhibitors p21Cip1 and p27Kip1. In INS-1 cells and islets, betacellulin- and IGF-I increased Akt, ERK, and p70S6 kinase phosphorylation. Rapamycin, an immunosuppressant which inhibits mTOR, inhibited the increase in p70S6 kinase phosphorylation stimulated by betacellulin- and IGF-I in INS-1 cells. Rapamycin also inhibited betacellulin- and IGF-I-induced entry of cells into S phase and BrdU incorporation as well as the effect of betacellulin and IGF-I on cyclin D1 expression and nuclear exclusion of p21Cip1 and p27Kip1. Together, these data suggest that the effect of betacellulin and IGF-I on islet cell growth and proliferation is mediated, in part, via signaling through mTOR. As rapamycin is used to treat islet transplant recipients, these results suggest that rapamycin could have deleterious effects on islet proliferation and function over time.

Tacrolimus Inhibits the Revascularization of Isolated Pancreatic Islets

“…This also suggests a relatively lesser role for donor islet endothelial cells in revascularization process of islet grafts as shown by previous reports [27], [37]. Although rapamycin was reported to have deleterious effects on islet viability and growth factor-induced cell cycle regulation [38], [39], the present study suggests that tacrolimus appears to have no inhibitory effects on cell cycle regulation.…”

Activation of Protein Kinase C-ζ in Pancreatic β-Cells In Vivo Improves Glucose Tolerance and Induces β-Cell Expansion via mTOR Activation

“…mTOR nucleates two distinct multiprotein complexes: mTOR complex 1 (mTORC1) and 2 (mTORC2) ( 40 , 41 ). mTORC1 is sensitive to rapamycin and is a major modulator of cell-cycle progression in β-cells by regulating the levels of D-cyclins ( 28 , 42 ). Rapamycin has been shown to inhibit β-cell proliferation in vitro and in vivo and to downregulate growth factor–induced D-cyclin expression ( 29 , 42 , 43 ).…”

“…mTORC1 is sensitive to rapamycin and is a major modulator of cell-cycle progression in β-cells by regulating the levels of D-cyclins ( 28 , 42 ). Rapamycin has been shown to inhibit β-cell proliferation in vitro and in vivo and to downregulate growth factor–induced D-cyclin expression ( 29 , 42 , 43 ). In follicular lymphoma cells, PKC-ζ inhibition leads to decreased mTOR activity, suggesting that PKC-ζ regulates mTOR in these cells ( 13 ).…”

Islet cell transplantation for Type 1 diabetes

“…Currently, many centers are using modified immunosuppression protocols to minimize these side effects. In addition, sirolimus has potent antiproliferative effects that prevent β‐cell regeneration 30 . Therefore, elimination of sirolimus from the protocol will avoid these side effects and may enhance β‐cell regeneration.…”

“…In addition, sirolimus has potent antiproliferative effects that prevent b-cell regeneration. 30 Therefore, elimination of sirolimus from the protocol will avoid these side effects and may enhance b-cell regeneration. Recently, we eliminated sirolimus from our protocol.…”