AJP - Endocrinology and Metabolism, Vol 263, Issue 5 E828-E836, Copyright © 1992 by American Physiological Society
Selective expression of an arachidonate 12-lipoxygenase by pancreatic islet beta-cells
V. R. Shannon, S. Ramanadham, J. Turk and M. J. Holtzman
Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110.
The immunohistochemical distribution of arachidonate lipoxygenases in rat
pancreas was characterized with specific polyclonal anti-5-lipoxygenase and
anti-12-lipoxygenase antibodies. Immunohistochemical analysis of
formaldehyde-fixed paraffin-embedded rat pancreas using
anti-12-lipoxygenase antibody and biotin-avidin-peroxidase detection
demonstrated specific staining of islets and no staining of pancreatic
exocrine tissue. Less intense staining of pancreatic vascular myocytes and
endothelial cells was also observed. Immunoblotting of isolated pancreatic
islet extracts with the anti-12-lipoxygenase antibody demonstrated
immunoperoxidase staining of a single protein band which comigrated with
purified 12-lipoxygenase (relative molecular weight = 72,000) on sodium
dodecyl sulfate-polyacrylamide gel electrophoresis analysis. Dispersed
cells prepared from isolated islets and then subjected to
fluorescence-activated cell sorting and immunostaining exhibited
12-lipoxygenase antigen in beta-cell populations but not in non-beta-cell
(predominantly alpha-cell) populations. Assays of enzymatic activity
confirmed that the 12-lipoxygenase-catalyzed conversion of arachidonic acid
to 12-hydroxyeicosatetraenoic acid methyl ester occurred only with purified
beta-cells and not with islet non-beta-cells. No evidence of 5-lipoxygenase
antigen or enzymatic activity was found in purified beta-cells or in islet
non-beta-cells. We conclude that rat pancreatic islet beta-cells contain an
arachidonate 12-lipoxygenase which shares antigenic epitopes with the
homologous enzyme contained in tissues from other species. In addition, the
selective localization of the 12-lipoxygenase to pancreatic beta-cells and
its absence in pancreatic acinar cells and in islet non-beta-cells support
observations suggesting that 12-lipoxygenase products may participate in
glucose-induced insulin secretion from beta-cells.
