Characterization of serine/threonine protein phosphatases in RINm5F insulinoma cells |
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| Authors: | Åke Sjöhom Richard E Honkanen Per-Olof Berggren |
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| Institution: | (1) Cancer Research Center of Hawaii, Molecular Oncology Program, University of Hawaii at Manoa, 1236 Lauhala Street, 96813 Honolulu, HI, USA;(2) Department of Endocrinology, The Rolf Luft Center for Diabetes Research, Karolinska Institute, Karolinska Hospital, S-171 76 Stockholm, Sweden;(3) Department of Internal Medicine, Löwenströmska Hospital, S-194 89 Upplands Väsby, Sweden;(4) Department of Biochemistry (MSB 2198), College of Medicine, University of South Alabama, 36688 Mobile, AL, USA |
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| Abstract: | 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, IC10010–6M), 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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| Keywords: | insulin secretion insulinoma okadaic acid protein phosphatase |
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