This study investigates the occurrence and regulation of serine/threonine protein phosphatases (PPases) in insulin-secreting RINm5F insulinoma cells. PPases types 1 and 2A were identified in crude RINm5F cell homogenates by both enzymatic assay and Western blot analysis. We then characterized and compared the inhibitory actions of several compounds isolated from cyanobacteria, marine dinoflagellates and marine sponges, (viz. okadaic acid, microcystin-LR, calyculin-A and nodularin) cation-independent PPase activities in RINm5F cell homogenates. It was found that okadaic acid was the least potent inhibitor (IC50 ≈ 10−9M, IC100 ≈ 10−6M), while the other compounds exhibited IC50 values of ≈ 5·10−10 M and IC100 ≈ 5·10−9 M. The findings indicate that the inhibitory substances employed in this study may be used pharmacologically to investigate the role of serine/threonine PPases in RINm5F cell insulin secretion, a process that is likely to be regulated to a major extent by protein phosphorylation.
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Research Article|
December 01 1993
Characterization of serine/threonine protein phosphatases in RINm5F insulinoma cells
Åke Sjöhom;
Åke Sjöhom
1University of Hawaii at Manoa, Cancer Research Center of Hawaii, Molecular Oncology Program, 1236 Lauhala Street, Honolulu, HI 96813, USA
2Department of Endocrinology, The Rolf Luft Center for Diabetes Research, Karolinska Institute, Karolinska Hospital, S-171 76 Stockholm, Sweden
3Department of Internal Medicine, Löwenströmska Hospital, S-194 89 Upplands Väsby, Sweden
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Richard E. Honkanen;
Richard E. Honkanen
1University of Hawaii at Manoa, Cancer Research Center of Hawaii, Molecular Oncology Program, 1236 Lauhala Street, Honolulu, HI 96813, USA
4Department of Biochemistry (MSB 2198), College of Medicine, University of South Alabama, Mobile AL 36688, USA
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Per-Olof Berggren
Per-Olof Berggren
2Department of Endocrinology, The Rolf Luft Center for Diabetes Research, Karolinska Institute, Karolinska Hospital, S-171 76 Stockholm, Sweden
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Publisher: Portland Press Ltd
Received:
September 29 1993
Accepted:
October 22 1993
Online ISSN: 1573-4935
Print ISSN: 0144-8463
© 1993 Plenum Publishing Corporation
1993
Biosci Rep (1993) 13 (6): 349–358.
Article history
Received:
September 29 1993
Accepted:
October 22 1993
Citation
Åke Sjöhom, Richard E. Honkanen, Per-Olof Berggren; Characterization of serine/threonine protein phosphatases in RINm5F insulinoma cells. Biosci Rep 1 December 1993; 13 (6): 349–358. doi: https://doi.org/10.1007/BF01150479
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