Insulin biosynthesis in HIT cells. Effects of glucose, forskolin, IBMX, and dexamethasone.
Glucose, forskolin, 3-isobutyl-1-methylxanthine (IBMX), and dexamethasone were tested as regulators of proinsulin biosynthesis in HIT T-15 cells, which are glucose-responsive simian virus 40-transformed hamster beta-cells. Rate of [3H]leucine incorporation into proinsulin was increased as glucose concentrations were raised from 0 to 20 mM. Biosynthetic rate increases were significant after 48 but not at 4 or 24 h of glucose and were greater for proinsulin than for total extractable proteins. After 48 h, glucose-stimulated proinsulin biosynthesis was unaffected by 10(-6) M forskolin and/or 3 x 10(-5) M IBMX but was specifically and significantly inhibited by 10(-6) M dexamethasone. Four hours of exposure to dexamethasone had no effect. When cells were incubated for 24 h and then continuously labeled for an additional 24 h, cellular conversion of labeled proinsulin to insulin was increased by glucose, and this increase was reversed or inhibited by 10(-6) M dexamethasone. Therefore, proinsulin biosynthesis in transformed HIT T-15 cells is regulated in several ways by metabolites and hormones in a manner that compares with biosynthetic regulation in normal beta-cells.
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Metabolic Research Unit, University of California, San Francisco 94143.
Qian
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Grodsky
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D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D002472:Cell Transformation, Viral; D005576:Colforsin / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000096:biosynthesis*; D007515:Islets of Langerhans / Q000378:metabolism*; D011384:Proinsulin / Q000096:biosynthesis; D013268:Stimulation, Chemical; D013997:Time Factors
D007328:Insulin; D005576:Colforsin; D003907:Dexamethasone; D011384:Proinsulin; D005947:Glucose; D015056:1-Methyl-3-isobutylxanthine