Isolation and characterization of pancreatic cancer (PC) diabetogenic factor: a 14 aminoacids peptide corresponding to the N-terminal sequence of an S-100 calcium binding protein

Introduction: Pancreatic cancer (PC)-associated diabetes is consequent to the action of a tumor peptide less than 10,000 Da. Our aim was to identify the PC-associated diabetogenic peptide. Methods: Tumor homogenates from PC patients with (n 15) or without (n 8) diabetes, and normal pancreas homogenates (n 6) were subjected to 16.5% SDS-PAGE. After Comassie staining a band of approximately 1500 Da was evidenced in tumor tissues only from diabetic PC. This band was cut and sequenced by automatic Adman degradation. Results: The sequence obtained revealed a 14 a peptide of 1589.88 Da, corresponding to the N-terminal sequence of an S-100 calcium binding protein. This peptide was synthesized and its effects on glucose metabolism were tested in cultured C2C12 my oblasts. These cells were cultured with different amounts (from 1 nmol/L to 2 mol/L) of the 14 a peptide. Glucose and lactate were measured in the supernatants after 24, 48 and 72 hours of incubation. In control my oblasts glucose concentration declined from 21.50 0.48 mol/L (mean SE) to 6.3 0.56, while lactate increased from 3.20 0.08 mol/L to 34.50 1.24 after 72 hours of incubation. 50nmol/L 14 a peptide caused a significant reduction in glucose consumption and in lactate production after 72 hours of incubation with respect to control (Student’s t test: t 3.87, p 0.05). At the same concentrations the 14 a peptide caused also my oblasts phenotypic alterations (accumulation of cells at the periphery of culture wells, lack of differentiation in myotubes and presence of polynucleated cells). Conclusions: The N-terminal 14 aa peptide from an S-100 calcium binding protein is produced by PC causing diabetes mellitus; this peptide impairs glucose catabolism by myoblasts in vitro and this might determine hyperglycemia in vivo; its identification in patients’ biological fluids might be helpful to diagnose PC when a recent onset diabetes mellitus occurs.