Demonstration of new sites of expression of the CCK-B/gastrin receptor in pancreatic acinar AR42J cells using immunoelectron microscopy

The CCK-B/gastrin receptor has been characterised in both normal and tumour tissues. Endocytosis of the CCK-B/gastrin receptor has recently been demon strated and this has similarly been described for other peptide receptors. In addition, ligand and ligand-receptor translocation to the nucleus has be en demonstrated for other peptides, The aim of this study was to identify t he sites of expression of the CCK-B/gastrin receptor in the known CCK-B/gas trin receptor bearing pancreatic acinar AR42J cells. The specificity of the CCK-B/gastrin receptor antibody (alpha-CCKBR-Ser antibody) was demonstrate d by inhibition ELISA studies, radioligand inhibition studies and immunoflu orescence binding studies on AR42J cells. Western blotting and immunogold e lectron microscopy techniques were used to identify the receptor in AR42J c ell preparations. The affinity purified alpha-CCKBR-Ser antibody was shown to be specific for the CCK-B/gastrin receptor. The receptor was expressed o n the cell membrane, in the cytoplasm and within the nucleus. Isoforms of t he receptor protein identified in extra-nuclear and nuclear extracts ranged in molecular weight from 58 to 66 kDa. We conclude that the CCK-B/gastrin receptor is not only expressed on the cell membrane, but also in the cytopl asm and nucleus of AR42J pancreatic acinar cells, (C) 1999 Elsevier Science B.V. All rights reserved.