Inhibition of Prenylation Promotes Caspase 3 Activation, Lamin B Degradation and Loss in Metabolic Cell Viability in Pancreatic β-Cells

Abstract

Background/Aims: Lamins are intermediate filament proteins that constitute the main components of the lamina underlying the inner-nuclear membrane and serve to organize chromatin. Lamins (e.g., lamin B) undergo posttranslational modifications (e.g., isoprenylation) at their C-terminal cysteine residues. Such modifications are thought to render optimal association of lamins with the nuclear envelop. Using human islets, rodent islets, and INS-1 832/13 cells, we recently reported significant metabolic defects under glucotoxic and endoplasmic reticulum (ER) stress conditions, including caspase 3 activation and lamin B degradation. The current study is aimed at further understanding the regulatory roles of protein prenylation in the induction of the aforestated metabolic defects. Methods: Subcellular phase partitioning assay was done using Triton X-114. Cell morphology and metabolic cell viability assays were carried out using standard methodologies. Results: We report that exposure of pancreatic β-cells to Simvastatin, an inhibitor of mevalonic acid (MVA) biosynthesis, and its downstream isoprenoid derivatives, or FTI-277, an inhibitor of farnesyltransferase that mediates farnesylation of lamins, leads to activation of caspase 3 and lamin B degradation. Furthermore, Simvastatin-treatment increased activation of p38MAPK (a stress kinase) and inhibited ERK1/2 (regulator of cell proliferation). Inhibition of farnesylation also resulted in the release of degraded lamin B into the cytosolic fraction and promoted loss in metabolic cell viability. Conclusion: Based on these findings we conclude that protein prenylation plays key roles in islet β-cell function. These findings affirm further support to the hypothesis that defects in prenylation pathway induce caspase-3 activation and nuclear lamin degradation in pancreatic β-cells under the duress of metabolic stress (e.g., glucotoxicity).

The Evolution of Cholesterol-Rich Membrane in Oxygen Adaption: The Respiratory System as a Model

“…It is possible that after an atmospheric increase in PO 2 , sterols biosynthesis was co-opted to rapidly evolve diverse cellular processes as a strategy to maintain optimal oxygen levels for productive growth and maintenance of biological functions (Figure 2). With the increase in complexity of sterols, particularly in eukaryotes, cholesterol biosynthesis pathways became intertwined with a wide range of molecular events [i.e., insulin secretion and beta-cell physiology (Tsuchiya et al, 2010; Zuniga-Hertz et al, 2015; Veluthakal et al, 2016; Syeda and Kowluru, 2017), intracellular pathway regulation by isoprenylation (Yang et al, 2015; Zhang X. et al, 2018), brain and neuronal function (Sun et al, 2015; Moutinho et al, 2016, 2017; Berghoff et al, 2017; Ferris et al, 2017; Paul et al, 2018), cardiac and myocytes physiology (Haque et al, 2016; Gadeberg et al, 2017; Hissa et al, 2017; Russell et al, 2017), cellular membrane-associated events (Kreutzberger et al, 2015; Stratton et al, 2016; Yang et al, 2016; Guixa-Gonzalez et al, 2017)]. In this sense, cholesterol can be considered as a molecular hub and a major control point for the rise and evolution of life as it currently exists.…”

Hyperglycemic Conditions Promote Rac1-Mediated Serine536 Phosphorylation of p65 Subunit of NFκB (RelA) in Pancreatic Beta Cells

“…At the outset, we used two structurally distinct inhibitors to assess the roles of protein prenylation in the cascade of events leading to HG-induced phosphorylation of p65. The first is Simvastatin (SMV), a known inhibitor of the cholesterol biosynthetic pathway, which depletes the intracellular pools of mevalonic acid, and its downstream intermediates, such as isoprenyl pyrophosphates that are required for protein prenylation (i.e., farnesylation and geranylgeranylation) [36,38,39]. The second inhibitor that we employed is L-788,123, which inhibits G protein (e.g., Rac1) prenylation via inhibition of farnesyl transferase (FTase) and geranylgeranyl transferase (GGTase) [40,41].…”

Targeting Small GTPases and Their Prenylation in Diabetes Mellitus

“… 197 , 198 Inhibition of prenylation using either statins or inhibitors of FTase induced a caspase-3-mediated decline in the levels of prenylated proteins, such as nuclear lamins, leading to β-cell dysregulation and death. 199 High-dose statin treatment slowed the progression of coronary atherosclerosis, resulting in disease regression in both diabetic and nondiabetic patients. 200 …”

“…197,198 Inhibition of prenylation using either statins or inhibitors of FTase induced a caspase-3-mediated decline in the levels of prenylated proteins, such as nuclear lamins, leading to β-cell dysregulation and death. 199 High-dose statin treatment slowed the progression of coronary atherosclerosis, resulting in disease regression in both diabetic and nondiabetic patients. 200 Although several questions remain unanswered, statins increase T2D risk, with some statins showing a stronger association (e.g., simvastatin, rosuvastatin, and atorvastatin) than others (e.g., pravastatin).…”

“…High concentrations of statins induced β-cell apoptosis and further reduced insulin secretion. In addition, by suppressing GLUT4, statins reduce glucose uptake in human skeletal muscle cells and adipocytes. , Also, treatment with statins, which results in an increase of cholesterol uptake in the β-cell, leads to reduced protein expression of GLUT2, hence limiting glucose uptake. , Inhibition of prenylation using either statins or inhibitors of FTase induced a caspase-3-mediated decline in the levels of prenylated proteins, such as nuclear lamins, leading to β-cell dysregulation and death . High-dose statin treatment slowed the progression of coronary atherosclerosis, resulting in disease regression in both diabetic and nondiabetic patients …”