PTBP1 and pancreatic insulinoma: Glucose stimulation of rat insulinoma INS-1 cells for 2 h led to a significant increase in the amounts of insulin 1 and 2 and the secretory granule markers ICA512/IA-2, PC1/3 and PC2 mRNAs co-immunoprecipitated with Polypyrimidine Tract Binding Protein 1 (PTBP1).