Metabolic Stress Induces Caspase-3 Mediated Degradation and Inactivation of Farnesyl and Geranylgeranyl Transferase Activities in Pancreatic β-Cells

• Published in: Cellular physiology and biochemistry Vol. 39; no. 6; pp. 2110 - 2120
• Main Authors: Veluthakal, Rajakrishnan, Arora, Daleep K., Goalstone, Marc L., Kowluru, Renu A., Kowluru, Anjaneyulu
• Format: Journal Article
• Language: English
• Published: Basel, Switzerland Cell Physiol Biochem Press GmbH & Co KG 01-01-2016
• Subjects: Adult; Alkyl and Aryl Transferases - metabolism; Animals; Biosynthetic Pathways - drug effects; Caspase 3 - metabolism; Cholesterol - biosynthesis; Endoplasmic Reticulum Stress - drug effects; Enzyme Activation - drug effects; Farnesylation; G-proteins; Geranylgeranylation; Glucose - toxicity; Humans; Insulin - metabolism; Insulin Secretion; Insulin-Secreting Cells - drug effects; Insulin-Secreting Cells - enzymology; Islet β-cell; Lipids - toxicity; Male; Metabolic stress; Models, Biological; Original Paper; Protein Prenylation - drug effects; Proteolysis - drug effects; Rats; Simvastatin - pharmacology; Stress, Physiological - drug effects; Geranylgeranylation; Islet β-cell; G-proteins; Farnesylation; Metabolic stress
• ISSN: 1015-8987; 1421-9778
• DOI: 10.1159/000447907

Background/Aims: At least 300 prenylated proteins are identified in the human genome; the majority of which partake in a variety of cellular processes including growth, differentiation, cytoskeletal organization/dynamics and vesicle trafficking. Aberrant prenylation of proteins is implicated in human pathologies including cancer; neurodegenerative diseases, retinitis pigmentosa, and premature ageing syndromes. Original observations from our laboratory have demonstrated that prenylation of proteins [small G-proteins and γ-subunits of trimeric G-proteins] is requisite for physiological insulin secretion. Herein, we assessed the impact of metabolic stress [gluco-, lipotoxicity and ER-stress] on the functional status of protein prenylation pathway in pancreatic β-cells. Methods: Farnesyltransferase [FTase] and geranylgeranyltransferase [GGTase] activities were quantified by radioisotopic methods. Caspase-3 activation and FTase/GGTase-α subunit degradation were determined by Western blotting. Results: We observed that metabolic stress activates caspase-3 and induces degradation of the common α-subunit of FTase and GGTase-I in INS-1 832/13 cells, normal rodent islets and human islets leading to functional defects [inactivation] in FTase and GGTase activities. Caspase-3 activation and FTase/GGTase-α degradation were also seen in islets from the Zucker diabetic fatty [ZDF] rat, a model for Type 2 diabetes. Consequential to defects in FTase/GGTase-α signaling, we observed significant accumulation of unprenylated proteins [Rap1] in β-cells exposed to glucotoxic conditions. These findings were replicated in β-cells following pharmacological inhibition of generation of prenylpyrophosphate substrates [Simvastatin] or catalytic activity of prenylating enzymes [GGTI-2147]. Conclusions: Our findings provide the first evidence to suggest that metabolic stress induced dysfunction of the islet β-cell may, in part, be due to defective protein prenylation signaling pathway.