Progressive development of gap junctions during growth of human pancreatic duct cells (Capan‐1) in vitro and in vivo

Abstract

Among their numerous functions, gap junctions play a crucial role in proliferation, differentiation and secretion processes, although their existence and potential role in ion secretion in human pancreatic ducts have yet to be established. To investigate the morphogenesis and the role of gap junctions in human pancreatic duct cells, the Capan-1 cell line maintained in culture or heterotransplanted into nude mice was employed as model system. Capan-1 cells polarize during their growth in vivo and in vitro forming duct-like structures. Furthermore in culture, after confluence, these cells form domes, which is indicative of ion exchange processes. After treatment with tannic acid and freeze-fracture, gap junctions were observed along the basolateral membranes of Capan-1 cells on electron microscopic examination. The presence of alkaline phosphatases on gap junctions was demonstrated cytoenzymatically. In addition, cell-to-cell communication was visualized by microinjection of Lucifer yellow. During differentiation of Capan-1 cells in culture, the frequency of intercellular communications increased markedly over the period (days 11-13) when the cells form duct-like structures. The increase in gap junctions was demonstrated by analysis of the polarized cells organized in duct-like structures that are commonly observed in the tumors formed by heterotransplantation of Capan-1 cells into nude mice. Furthermore, gap junctions associated with tight junctions were also observed in the cells forming such structures. The role of gap junctions in ion exchange was evaluated by counting the number of domes in cultures treated with heptanol. Heptanol (an uncoupling agent of gap junction communication) completely inhibited dome formation in a reversible way, and reduced the frequency of intracellular communications by 44%. These results suggest that the gap junctions expressed by Capan-1 cells are involved in ion secretion by the human cancerous pancreatic duct cell line, Capan-1. In the present study, we show that: i) the expression of gap junctions is linked to development of the spatial conformation of the cells; and ii) gap junctions may be involved in ion secretion.

Secretin Increases the Paracellular Permeability of CAPAN-1 Pancreatic Duct Cells

“…Dome formation and maintenance require vectorial ion fluxes, typical of the differentiated phenotype, and the presence of tight junctional complexes (28). In the same cell model employed here dome formation is associated with the appearance of both gap and tight junctions (27,37). It is, therefore, hardly surprising that brefeldin A and PDBu, known to perturb tight junctions in other cell models (31)(32)(33), completely suppress domes in CAPAN-1 cells.…”

Two Cytologic Patterns in Invasive Ductal Adenocarcinoma of the Pancreas

“…21 According to Monzat et al, 24 gap junctions play a crucial role in proliferation, differentiation and secretion processes, and during the growth of human pancreatic duct cells in vitro and in vivo, gap junctions develop progressively. Hence, clearly defined cytoplasmic borders seem to result from the double factors of highly developed gap junction intercellular communication, reflecting welldifferentiated duct cells, and pressure on the cytoplasmic border due to excessive proliferation.…”