Effect of chronic excess of tumour necrosis factor-alpha on contractile proteins in rat skeletal muscle.

The effect of chronic tumour necrosis factor-alpha (TNF-alpha) treatment on the synthesis of specific myofibrillar proteins such as heavy chain myosin, light chain myosin and G-actin in rat diaphragm were evaluated. Muscles (diaphragm) from control and experimental groups (TNF-alpha i.v. at 50 microg/kg body wt for 5 days) were incubated in the presence of 35S-methionine for 2 h. Myofibrillar protein extracts were prepared and protein was electrophoresed on sodium dodecyl sulphate-polyacrylamide gels. Heavy chain myosin, light chain myosin and G-actin were identified by Western blot analysis using specific monoclonal antibodies. Polyacrylamide gel electrophoresis (PAGE) followed by Western blot analysis revealed two types of heavy chain myosin (206 and 212 kD), all four types of light chain myosin (15, 16.5, 18 and 20 kD) and a single type of G-actin (42 kD). Chronic TNF-alpha treatment produced a significant decline in the synthesis of all types of myofibrillar proteins, namely heavy chain myosin, light chain myosin and G-actin. TNF-alpha impaired peptide-chain initiation in diaphragm muscle which was reversed by the branched-chain amino acids (BCAA) therapy of TNF-alpha treated rats. These findings indicate a significant role for TNF-alpha in the translational regulation of protein synthesis in skeletal muscle.

Effect of tumour necrosis factor-alpha on total myofibrillar and sarcoplasmic protein synthesis and polysomal aggregation in rat skeletal muscles.

The total sarcoplasmic and myofibrillar protein synthesis was reduced in incubated fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus of rat after in vivo tumour necrosis factor-alpha treatment at 50 micrograms/kg/day for 5 days. The rate of protein synthesis in the myofibrillar fraction was inhibited more severely (41% in EDL and 34% in soleus) than that in the sarcoplasmic fraction (23% in EDL and 14% in soleus). Sucrose density gradient centrifugation analysis indicated that TNF-alpha treatment impaired polysomal aggregation in rat diaphragm muscle. Compared with the control muscles, the ratio of 40S and 60S subunits to polysomes was higher in TNF-alpha treated muscles. These findings suggest a role for TNF-alpha in the translational regulation of protein synthesis in rat skeletal muscle.

The effect of histone-mRNA interaction in protein synthesis.

The effect of lysine-rich and arginine-rich histones on selective inhibition of translation of mRNAs of tobacco mosaic virus (TMV), brome mosaic virus (BMV) and luciferase, in rabbit reticulocyte (RRL) was evaluated. Nuclease-treated RRL were supplemented with an appropriate mRNA and incubated with lysine-rich or arginine-rich histones at 5 and 2.5 micrograms/100 microliters lysate at 30 degrees C. Protein synthesis was measured as incorporation of 3H-leucine into protein for 24 min. The lysine-rich histone was more inhibitory than arginine-rich histone. At 5 and 2.5 micrograms/100 microliters lysate concentration, the lysine-rich histone inhibited translation of TMV mRNA by 57% and 35%, respectively, after 24 min. The corresponding values for arginine-rich histone were 31% and 13%. Both histones had a more inhibitory effect on the translation of viral mRNA than luciferase mRNA. Arginine-rich histone at 2.5 micrograms/100 microliters lysate did not cause any inhibition of luciferase mRNA. The spectrophotometric analysis of histone-mRNA mixtures at 280 nm indicated that, compared with arginine-rich histone, lysine-rich histone had a stronger affinity for mRNA.