Role of the TSC1-TSC2 complex in the integration of insulin and glucose signaling involved in pancreatic beta-cell proliferation
Authors: Carlos Guillén
Alberto Bartolomé
Manuel Benito
Journal: Endocrinology (2010)
Discipline: BIOLOGY & BIOCHEMISTRY
Keywords: Tuberous sclerosis complex proteins 1-2; mTOR complex 1; insulin signaling; phosphatidylinositol 3-kinase; Akt
Affiliations: Departamento de Bioquímica y Biología Molecular (A.B., C.G., M.B.), Facultad de Farmacia, Universidad Complutense, 28040 Madrid, Spain, Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM) (A.B., C.G., M.B.), Mallorca 183, 08036 Barcelona, Spain

Abstract:  Tuberous sclerosis complex proteins 1-2 (TSC1-TSC2) complex integrates both nutrient and hormonal signaling and is a critical negative regulator of mammalian target of rapamycin (mTOR) complex 1. The use of different beta-cell lines expressing or not the insulin receptor (IR(+/+) and IR(-/-)) or with a reconstituted expression of IR isoform A or B (Rec A and Rec B) revealed that both phosphatidylinositol 3-kinase/Akt/TSC/mTOR complex 1 and MAPK kinase/ERK pathways mediate insulin signaling in IR(+/+)-, IRA-, or IRB-expressing cells. However, glucose signaling was mediated by MAPK kinase/ERK and AMP-activated protein kinase pathways as assessed in IR(-/-) cells. The effect of insulin on Akt phosphorylation was completely inhibited by the use of the phosphatidylinositol 3-kinase inhibitor wortmannin in IR(+/+) and Rec B cells, a partial inhibitory effect being observed in Rec A cell line. The knockdown of TSC2 expression up-regulated the downstream basal phosphorylation of 70-kDa ribosomal protein S6 kinase (p70S6K) and mTOR. More importantly, upregulation of p70S6K signaling impaired insulin-stimulated phosphorylation of Akt Ser(473) and p70S6K in IR(+/+) and Rec B but not in Rec A cell lines. In fact, insulin receptor substrate-1 Ser(307) phosphorylation signal in Rec B was stronger than in Rec A cell line during insulin action. Rec A cells induced a higher proliferation rate compared with Rec B or IR(+/+) during serum stimulation. Thus, we propose that the regulation of TSC2 phosphorylation by insulin or glucose independently integrates beta-cell proliferation signaling, the relative expression of IRA or IRB isoforms in pancreatic beta cells playing a major role. 

Retracted: No

PubPeer comments:
 Figure 4A: More similar than expected, could authors check please? ![file] , 
 Thanks to Siphocampylus fulgens for this comment. I have checked this figure and, indeed, these images were added by mistake during the elaboration of the final figure 4A. In fact, it is a very complex figure with many blots and experimental conditions. I have been able to find the original scans from these experiments and i send you attached the images at high resolution of the corresponding blots as well as two other replicates of the same experiment, in order to see the reproducibility of the experiments. In addition, checking for any other possible mistake in this figure, i have observed that in the IR- - cells (upper right panels of figure 4A), in the TSC1 protein, there is a missing lane that was totally involuntary cropped during the elaboration of the whole figure 4A. I send you the whole correct scanned image too.![file] ![file] ![file] ![file] It is important to say that these changes do not affect neither the conclusions made by the authors nor the validity of the results of this article, which has been confirmed by the scientific community. Best regards Carlos , 
 #2 Thanks for your reply.  *...these changes do not affect...* -- Does this mean the authors are going to ask for an erratum? , 
 #2 There s still something unclear to me. Regarding Akt IR+ +, if I understand correctly wat is what, the raw data looks actually quite different from the published one. For instance, in Exp 3 (first-from-up original blot shown) the intensity of bands is fading away in some lanes, which is not the case in the published (manipulated) version, which in turn seems more similar to Exp 2 (second-from-up original blot shown) that seems anyway a bit overexposed. Then again the raw data looks different in the third-from-up original blot shown. Am I missing something here? , 
 Thanks to Aneurus inconstans for the comment. The experiment 3 is a replicate of the experiment and was used to realized the statistical analysis but not presented in the manuscript. I have sent these another images, in order to demonstrate the reproducibility of the results. In any case, i re-send you again the two correct scanned images for the manuscript, which are highlighted in red Carlos![file] ,