Loss of insulin-induced inhibition of glucagon gene transcription in hamster pancreatic islet alpha cells by long-term insulin exposure

TY - JOUR

T1 - Loss of insulin-induced inhibition of glucagon gene transcription in hamster pancreatic islet alpha cells by long-term insulin exposure

AU - González, M

AU - Böer, U

AU - Dickel, C

AU - Quentin, T

AU - Cierny, I

AU - Oetjen, E

AU - Knepel, W

PY - 2008/11

Y1 - 2008/11

N2 - AIMS/HYPOTHESIS: Diabetes mellitus type 2 is characterised by hyperglucagonaemia, resulting in hepatic glucose production and hyperglycaemia. Considering that insulin inhibits glucagon secretion and gene transcription, hyperglucagonaemia in the face of hyperinsulinaemia in diabetes mellitus type 2 suggests that there is insulin resistance also at the glucagon-producing pancreatic islet alpha cells. However, the molecular mechanism of alpha cell insulin resistance is unknown. Therefore, the effect of molecules implicated in conferring insulin resistance in some other tissues was investigated on insulin-induced inhibition of glucagon gene transcription in alpha cells.METHODS: Reporter gene assays and biochemical techniques were used in the glucagon-producing hamster pancreatic islet alpha cell line InR1-G9.RESULTS: From among 16 agents tested, chronic insulin treatment was found to abolish insulin-induced inhibition of glucagon gene transcription. Overproduction of constitutively active protein kinase B (PKB) still inhibited glucagon gene transcription after chronic insulin treatment; together with a markedly reduced insulin-induced phosphorylation and, thus, activation of PKB, this indicates that targets upstream of PKB within the insulin signalling pathway are affected. Indeed, chronic insulin treatment markedly reduced IRS-1 phosphorylation, insulin receptor (IR) autophosphorylation and IR content. Cycloheximide and in vivo labelling experiments attributed IR downregulation to enhanced degradation.CONCLUSIONS/INTERPRETATION: These results show that an extended exposure of alpha cells to insulin induces IR downregulation and loss of insulin-induced inhibition of glucagon gene transcription. They suggest that hyperinsulinaemia, through IR downregulation, may confer insulin resistance to pancreatic islet alpha cells in diabetes mellitus type 2.

AB - AIMS/HYPOTHESIS: Diabetes mellitus type 2 is characterised by hyperglucagonaemia, resulting in hepatic glucose production and hyperglycaemia. Considering that insulin inhibits glucagon secretion and gene transcription, hyperglucagonaemia in the face of hyperinsulinaemia in diabetes mellitus type 2 suggests that there is insulin resistance also at the glucagon-producing pancreatic islet alpha cells. However, the molecular mechanism of alpha cell insulin resistance is unknown. Therefore, the effect of molecules implicated in conferring insulin resistance in some other tissues was investigated on insulin-induced inhibition of glucagon gene transcription in alpha cells.METHODS: Reporter gene assays and biochemical techniques were used in the glucagon-producing hamster pancreatic islet alpha cell line InR1-G9.RESULTS: From among 16 agents tested, chronic insulin treatment was found to abolish insulin-induced inhibition of glucagon gene transcription. Overproduction of constitutively active protein kinase B (PKB) still inhibited glucagon gene transcription after chronic insulin treatment; together with a markedly reduced insulin-induced phosphorylation and, thus, activation of PKB, this indicates that targets upstream of PKB within the insulin signalling pathway are affected. Indeed, chronic insulin treatment markedly reduced IRS-1 phosphorylation, insulin receptor (IR) autophosphorylation and IR content. Cycloheximide and in vivo labelling experiments attributed IR downregulation to enhanced degradation.CONCLUSIONS/INTERPRETATION: These results show that an extended exposure of alpha cells to insulin induces IR downregulation and loss of insulin-induced inhibition of glucagon gene transcription. They suggest that hyperinsulinaemia, through IR downregulation, may confer insulin resistance to pancreatic islet alpha cells in diabetes mellitus type 2.

KW - Adaptor Proteins, Signal Transducing

KW - Animals

KW - Cell Line

KW - Cricetinae

KW - Down-Regulation

KW - Enzyme Activation

KW - Gene Expression Regulation

KW - Glucagon

KW - Glucagon-Secreting Cells

KW - Insulin

KW - Insulin Receptor Substrate Proteins

KW - Interleukin-1beta

KW - Mice

KW - Mice, Inbred Strains

KW - Phosphorylation

KW - Plasmids

KW - Proto-Oncogene Proteins c-akt

KW - Transcription, Genetic

KW - Transfection

U2 - 10.1007/s00125-008-1134-5

DO - 10.1007/s00125-008-1134-5

M3 - SCORING: Journal article

C2 - 18762908

VL - 51

SP - 2012

EP - 2021

JO - DIABETOLOGIA

JF - DIABETOLOGIA

SN - 0012-186X

IS - 11

ER -