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Phosphoinositide metabolism in a polyoma‐bk‐virus‐transformed pancreatic islet cell line: Evidence for constitutively activated phospholipase C
Author(s) -
Giæver A. K.,
Husom Haukland H.,
Bertinussen A.,
Vonen B.,
Malm D.,
Huseby N. E.,
Florholmen J.
Publication year - 1993
Publication title -
international journal of cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.475
H-Index - 234
eISSN - 1097-0215
pISSN - 0020-7136
DOI - 10.1002/ijc.2910530116
Subject(s) - inositol , phosphatidylinositol , pertussis toxin , inositol phosphate , inositol trisphosphate , endocrinology , phospholipase c , medicine , pancreatic islets , neomycin , islet , biology , cholera toxin , chemistry , biochemistry , insulin , g protein , receptor , signal transduction , antibiotics
We have characterized the phosphoinositide metabolism in a polyoma‐BK‐virus‐transformed rat pancreatic islet cell line which has highly malignant characteristics, expresses viral T‐antigen and has lost insulin‐secreting capacity. After incorporation with [ 3 H]linositol to isotopic equilibrium, all inositol metabolites were analyzed. When comared with normal pancreatic islets, increased levels of inositol 1,4,5‐trisphosphate (Ins‐ 1,4,5‐P 3 ), inositol 1,3,4‐trisphosphates and inositol tetrakisphosphate (Ins‐P 4 ), and decreased levels of phosphatidylinositol monophosphate (PIP) and phosphatidylinositol bisphosphate (PIP 2 ) were found. The Ins‐1,4,5‐P 3 /PIP 2 ratio increased, whereas the PIP 2 /PIP ratio was not altered after the transformation. In the pancreatic islet cell line there was a stable accumulation of inositol phosphates at 3.3 mM glucose. Glucose, KCL, cholecystokinin (CCK) and carbachol with and without LiCL were all without effect on the accumulation of inositol phosphates. Somatostatin inhibited the accumulation of inositol phosphates but a Ca 2 +‐free/EDTA solution did not. Preincubation with cholera toxin or pertussis toxin inhibited the accumulation of inositol phosphates at 3.3 mM glucose except for Ins‐P 4 , whereas no effect was obsewed on the phosphoinositides. NaF stimulated the accumulation of inositol phosphates, with a concomitant decrease in the phosphoinositides, whereas neomycin was without effect on the inositol phosphates. In normal pancreatic islets, pertussis toxin inhibited the CCK‐ induced increase in Ins‐ 1,4,5‐P 3 , whereas no effect was seen at 3.3 mM glucose. Finally, pertussis toxin inhibited the CCK‐ induced increase in the Ins‐ 1,4,5‐P 3 /PIP 2 ratio in normal pancreatic islets. The same inhibition was also found in the pancreatic islet cell line at 3.3 mM glucose. We conclude that in the transformed pancreatic islet cell line the phosphoinositide hydrolysis is constitutively activated at the level of phospholipase C, with a substantial loss of regulatory control.