PHB1 and pancreatic insulinoma: After stimulation of the rat insulinoma cell line (INS-1E) with glucose, mitochondrial proteins involved in Ca2+ homeostasis, such as the voltage-dependent anion-selective channel (VDAC) protein, prohibitin, and different ATP synthase subunits, were discovered to be substrates of TG2 [57,112], indicating that TG2 activity is important in this process too.