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Effects of insulin-like growth factor-I, insulin, and leucine on protein turnover and ubiquitin ligase expression in rainbow trout primary myocytes.
- Source :
-
American Journal of Physiology: Regulatory, Integrative & Comparative Physiology . Feb2010, Vol. 298, pR341-R350. 10p. - Publication Year :
- 2010
-
Abstract
- The effects of insulin-like growth factor-I (IGF-I), insulin, and leucine on protein turnover and pathways that regulate proteolytic gene expression and protein polyubiquitination were investigated in primary cultures of 4-day-old rainbow trout myocytes. Supplementing media with 100 nM IGF-I increased protein synthesis by 13% (P < 0.05) and decreased protein degradation by 14% (P < 0.05). Treatment with 1 μM insulin increased protein synthesis by 13% (P < 0.05) and decreased protein degradation by 17% (P < 0.05). Supplementing media containing 0.6 mM leucine with an additional 2.5 mM leucine did not increase protein synthesis rates but reduced rates of protein degradation by 8% (P < 0.05). IGF-I (1 nM-100 nM) and insulin (1 nM1 μM) independently reduced the abundance of ubiquitin ligase mRNA in a dose-dependent manner, with maximal reductions of ∼70% for muscle atrophy F-box (Fbx) 32, 40% for Fbx25, and 25% for muscle RING finger-1 (MuRF1, P < 0.05). IGF-I and insulin stimulated phosphorylation of FOXO1 and FOXO4 (P < 0.05), which was inhibited by the phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor wortmannin, and decreased the abundance of polyubiquitinated proteins by 10-20% (P < 0.05). Supplementing media with leucine reduced Fbx32 expression by 25% (P < 0.05) but did not affect Fbx25 nor MuRF1 transcript abundance. Serum deprivation decreased rates of protein synthesis by 60% (P < 0.05), increased protein degradation by 40% (P < 0.05), and increased expression of all ubiquitin ligases. These data suggest that, similar to mammals, the inhibitory effects of IGF-I and insulin on proteolysis occur via PI 3-kinase/protein kinase B signaling and are partially responsible for the ability of these compounds to promote protein accretion. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 03636119
- Volume :
- 298
- Database :
- Academic Search Index
- Journal :
- American Journal of Physiology: Regulatory, Integrative & Comparative Physiology
- Publication Type :
- Academic Journal
- Accession number :
- 48141221
- Full Text :
- https://doi.org/10.1152/ajpregu.00516.2009