The pseudokinase tribbles homolog 3 interacts with ATF4 to negatively regulate insulin exocytosis in human and mouse beta cells.
Insufficient insulin secretion and reduced pancreatic beta cell mass are hallmarks of type 2 diabetes (T2DM). Here, we confirm that a previously identified polymorphism (rs2295490/Q84R) in exon 2 of the pseudokinase-encoding gene tribbles 3 (TRB3) is associated with an increased risk for T2DM in 2 populations of people of mixed European descent. Carriers of the 84R allele had substantially reduced plasma levels of C-peptide, the product of proinsulin processing to insulin, suggesting a role for TRB3 in beta cell function. Overexpression of TRB3 84R in mouse beta cells, human islet cells, and the murine beta cell line MIN6 revealed reduced insulin exocytosis, associated with a marked reduction in docked insulin granules visualized by electron microscopy. Conversely, knockdown of TRB3 in MIN6 cells restored insulin secretion and expression of exocytosis genes. Further analysis in MIN6 cells demonstrated that TRB3 interacted with the transcription factor ATF4 and that this complex acted as a competitive inhibitor of cAMP response element-binding (CREB) transcription factor in the regulation of key exocytosis genes. In addition, the 84R TRB3 variant exhibited greater protein stability than wild-type TRB3 and increased binding affinity to Akt. Mice overexpressing TRB3 84R in beta cells displayed decreased beta cell mass, associated with reduced proliferation and enhanced apoptosis rates. These data link a missense polymorphism in human TRB3 to impaired insulin exocytosis and thus increased risk for T2DM.
Liew
Chong Wee
CW
Section of Islet Cell and Regenerative Medicine, Department of Medicine, Harvard Medical School, Research Division, Joslin Diabetes Center, Boston, Massachusetts 02215, USA.
Bochenski
Jacek
J
Kawamori
Dan
D
Hu
Jiang
J
Leech
Colin A
CA
Wanic
Krzysztof
K
Malecki
Maciej
M
Warram
James H
JH
Qi
Ling
L
Krolewski
Andrzej S
AS
Kulkarni
Rohit N
RN
D051701:Activating Transcription Factor 4 / Q000502:physiology*; D000818:Animals; D017209:Apoptosis; D018797:Cell Cycle Proteins / Q000502:physiology*; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D003924:Diabetes Mellitus, Type 2 / Q000209:etiology; D004041:Dietary Fats / Q000008:administration & dosage; D005089:Exocytosis; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D017346:Protein Serine-Threonine Kinases / Q000502:physiology* / Q000037:antagonists & inhibitors; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011972:Receptor, Insulin / Q000502:physiology; D012097:Repressor Proteins / Q000502:physiology*
C497109:ATF4 protein, human; C081452:Atf4 protein, mouse; D018797:Cell Cycle Proteins; D017362:Cyclic AMP Response Element-Binding Protein; D004041:Dietary Fats; D007328:Insulin; D012097:Repressor Proteins; C474830:TRB3 protein, mouse; C474831:TRIB3 protein, human; D051701:Activating Transcription Factor 4; D011972:Receptor, Insulin; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases