A possible role of transglutaminase 2 in the nucleus of INS-1E and of cells of human pancreatic islets

Abstract

Transglutaminase 2 (TG2) is a multifunctional protein with Ca2 +-dependent transamidating and G protein activity. Previously we reported that the role of TG2 in insulin secretion may involve cytoplasmic actin remodeling and a regulative action on other proteins during granule movement. The aim of this study was to gain a better insight into the role of TG2 transamidating activity in mitochondria and in the nucleus of INS-1E rat insulinoma cell line (INS-1E) during insulin secretion. To this end we labeled INS-1E with an artificial donor (biotinylated peptide), in basal condition and after stimulus with glucose for 2, 5, and 8 min. Biotinylated proteins of the nuclear/mitochondrial-enriched fraction were analyzed using two-dimensional electrophoresis and mass spectrometry. Many mitochondrial proteins involved in Ca2 + homeostasis (e.g. voltage-dependent anion-selective channel protein, prohibitin and different ATP synthase subunits) and many nuclear proteins involved in gene regulation (e.g. histone H3, barrier to autointegration factor and various heterogeneous nuclear ribonucleoprotein) were identified among a number of transamidating substrates of TG2 in INS-1E. The combined results provide evidence that a temporal link exists between glucose-stimulation, first phase insulin secretion and the action of TG on histone H3 both in INS-1E and human pancreatic islets.Biological significanceResearch into the role of transglutaminase 2 during insulin secretion in INS-1E rat insulinoma cellular model is depicting a complex role for this enzyme. Transglutaminase 2 acts in the different INS-1E compartments in the same way: catalyzing a post-translational modification event of its substrates. In this work we identify some mitochondrial and nuclear substrates of INS-1E during first phase insulin secretion. The finding that TG2 interacts with nuclear proteins that include BAF and histone H3 immediately after (2–5 min) glucose stimulus of INS-1E suggests that TG2 may be involved not only in insulin secretion, as suggested by our previous studies in cytoplasmic INS-1E fraction, but also in the regulation of glucose-induced gene transcription.

Characterization of the Molecular Mechanisms Underlying Glucose Stimulated Insulin Secretion from Isolated Pancreatic β-cells Using Post-translational Modification Specific Proteomics (PTMomics)

“…Interestingly, in this study the glucose-regulated proteins were mostly downregulated after 5 min of stimulation, whereas most of the upregulated proteins were found after 10 and 15 min of glucose stimulation. Putative regulators after 5 min of high glucose stimulation might be linked with intracellular Ca 2ϩ homeostasis, because dynamic changes in Ca 2ϩ concentration was observed in the nucleus and the mitochondrion of rat ␤-cells (INS-1E) during the first 2-5 min of high glucose stimulation (42,43). However, the roles of nuclear proteins have not yet been examined in a large-scale study.…”

Modification of histone proteins by serotonin in the nucleus

“…The problems associated with PTAA and spiro-OMeTAD have stimulated the search for alternatives. Cheaper, dopant-free materials for transporting holes have been reported [5][6][7] , as well as new stable dopants 8 , but the powerconversion efficiencies of perovskite solar cells made using these materials cannot compete with those of devices that use PTAA or spiro-OMeTAD. Finding low-cost hole-transport materials that provide both high efficiency and stability, and that are compatible with the industrial processes used to make solar cells, remains challenging.…”

“…Although serotonylation in the nucleus had not previously been described, some intriguing hints supported its existence. A small fraction of the total amount of the enzyme transglutaminase 2 (TGM2) in cells 8 , as well as a portion of the cells' serotonin content 9 , were found in the nucleus. These observations suggested that serotonylation could target nuclear proteins, and thereby influence gene expression independently of serotonin receptors and their signalling pathways.…”

Tissue transglutaminase TG2 and mitochondrial function and dysfunction

“…As reversible and repetitive structural changes are required for ligandgated ion channels to mediate biological signaling, TG2 crosslinking chronically impaired calcium signaling and autophagy regulation in living cells (126). Upon stimulation of rat insulinoma cell line (INS-1E) with glucose, many mitochondrial proteins involved in Ca +2 homeostasis including voltagedependent anion-selective channel (VDAC) protein, prohibitin, and different ATP synthase subunits were found to be the TGase substrates of TG2 (129). VDACs are part of a network which includes the IP3Rs, stress-70 protein, a mitochondrial chaperone that facilitate mitochondrial Ca +2 uptake, and calreticulin (129).…”

“…Upon stimulation of rat insulinoma cell line (INS-1E) with glucose, many mitochondrial proteins involved in Ca +2 homeostasis including voltagedependent anion-selective channel (VDAC) protein, prohibitin, and different ATP synthase subunits were found to be the TGase substrates of TG2 (129). VDACs are part of a network which includes the IP3Rs, stress-70 protein, a mitochondrial chaperone that facilitate mitochondrial Ca +2 uptake, and calreticulin (129).…”