In:
Journal of Endocrinology, Bioscientifica, Vol. 193, No. 1 ( 2007-04), p. 45-51
Abstract:
Calpains are a family of non-lysosomal cytoplasmatic cysteine proteases. Since calpain 10 (CAPN10), a member of the calpain family of proteases, has been found to represent a putative diabetes susceptibility gene, it was argued that calpains may be involved in the development of type 2 diabetes. The functional role of calpains in insulin signaling and/or insulin action is, however, not clear. We investigated the effects of the calpains 1 and 2 inhibitor PD151746 on insulin signaling and insulin action in human hepatoma G2 cells (HepG2). HepG2 cells were incubated without (−PD) or with (+PD) 5.33 μmol/l PD151746 for different times and then stimulated with 100 nmol/l insulin for 0 ( t 0 ), 5 ( t 5 ), 15 ( t 15 ), 30 ( t 30 ), 45 ( t 45 ), and 60 ( t 60 ) min. After solubilization of the cells, insulin receptor kinase activity, tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1), IRS-1-associated phosphatidylinositol-3 kinase (PI3-kinase), PI3-kinase activity, Thr 308 phosphorlyation of Akt, amount of protein tyrosine phosphatase-ε (PTPε), and glycogen synthase activity were determined. Incubation with PD151746 resulted in a significant reduction of insulin-stimulated glycogen synthesis compared with cells not pre-incubated with the calpain inhibitor (−PD: t 0 , 4.90 ± 1.20%; t 5 , 5.90 ± 1.02%; t 15 , 5.29 ± 0.95%; t 30 , 5.60 ± 1.10%; t 45 , 5.52 ± 0.90%; t 60 , 5.67 ± 0.97%;+PD: t 0 , 4.56 ± 1.10%; t 5 , 6.16 ± 1.05%; t 15 , 7.52 ± 1.09%; t 30 , 7.68 ± 1.10%; t 45 , 8.28 ± 0.89%; t 60 , 7.69 ± 0.98%; P 〈 0.05). Incubation with PD151746 significantly increased the protein amount of PTPε in the cells after 12 h (−PD: t 1 , 0.85 ± 0.18 RU (Relative unit); t 8 , 0.87 ± 0.18 RU; t 12 , 0.9 ± 0.13 RU; +PD: t 1 , 0.92 ± 0.21 RU; t 8 , 1.1 ± 0.15 RU; t 12 , 1.34 ± 0.16 RU; P 〈 0.05). Calpain inhibition with PD151746 had no effect on the insulin stimulation of the investigated insulin signaling parameters. These results in HepG2 cells suggest that calpains play a role in the hepatic regulation of insulin-stimulated glycogen synthesis independent of the PI3-kinase/Akt signaling pathway.
Type of Medium:
Online Resource
ISSN:
0022-0795
,
1479-6805
Language:
Unknown
Publisher:
Bioscientifica
Publication Date:
2007
detail.hit.zdb_id:
1474892-7
