Serum Deprivation Induces Glucose Response and Intercellular Coupling in Human Pancreatic Adenocarcinoma PANC-1 Cells

PANC-1 cells are an established line of human pancreatic adenocarcinoma (PAC). Hui et al,1 Hardikar et al,2 and Wu et al3 reported that PANC-1 cells, when changed from serum-containing growth medium to serum-free medium (SFM), undergo differentiation and start expressing glucagon, somatostatin, and insulin. The initial process involves aggregation to form spherical clusters that morphologically resemble pancreatic islets accompanied by mesenchymal-to-epithelial transition.3,4 We have previously reported that PANC-1 cells express 3 subtypes of proteinase-activated receptors (PARs 1, 2, 3).5 The stimulation of PAR-1 or PAR-2 evokes cytosolic free calcium ([Ca]i) transients and accelerates PANC-1 cell aggregation in SFM.5,6 β-Cells secrete insulin in response to glucose. This signaling mechanism depends on glucose metabolism and requires the functional presence of glucose sensing machinery. The first step is a rapid glucose uptake facilitated by GLUT2, followed by its phosphorylation and entrance into the glycolytic cycle leading to elevation of the ATP/ADP ratio. The increase in the ATP/ADP ratio causes closure of K(ATP) channels resulting in depolarization, activation of L-type voltage-sensitive calcium channels (VSCCs) and a rise in [Ca]i leading to insulin secretion.7 Fully differentiated β cells in islets form a characteristic syncytium that underlies coordinated calcium signaling and insulin secretion.8–10 Indeed, single β cells, which cannot establish intercellular communication via gap junctions, show alterations in secretion and insulin gene expression, which are corrected after restoration of β-cell contacts.11–13 Hence, the emergence of glucose signaling and the existence of intercellular communication are hallmarks of functional β-cell differentiation. The present report addresses the question whether the early aggregation and differentiation of PANC-1 cells is accompanied by the emergence of functional glucose signaling machinery and of intercellular communication, as well as the effect of activation of PAR-2 receptors on these processes. We show that differentiating PANC-1 cell clusters exhibit glucose signaling and intercellular transport of a marker fluorescent probe. The activation of the glucose signaling pathway is modestly enhanced by a low concentration of trypsin.