Differential regulation of MAP kinase, p70(S6K), and Akt by contraction and insulin in rat skeletal muscle.

To study the effects of contractile activity on mitogen-activated protein kinase (MAP kinase), p70 S6 kinase (p70(S6K)), and Akt kinase signaling in rat skeletal muscle, hindlimb muscles were contracted by electrical stimulation of the sciatic nerve for periods of 15 s to 60 min. Contraction resulted in a rapid and transient activation of Raf-1 and MAP kinase kinase 1, a rapid and more sustained activation of MAP kinase and the 90-kDa ribosomal S6 kinase 2, and a dramatic increase in c-fos mRNA expression. Contraction also resulted in an apparent increase in the association of Raf-1 with p21Ras, although stimulation of MAP kinase signaling occurred independent of Shc, IRS1, and IRS2 tyrosine phosphorylation or the formation of Shc/Grb2 or IRS1/Grb2 complexes. Insulin was considerably less effective than contraction in stimulating the MAP kinase pathway. However, insulin, but not contraction, increased p70(S6K) and Akt activities in the muscle. These results demonstrate that contraction-induced activation of the MAP kinase pathway is independent of proximal steps in insulin and/or growth factor-mediated signaling, and that contraction and insulin have discordant effects with respect to the activation of the MAP kinase pathway vs. p70(S6K) and Akt. Of the numerous stimulators of MAP kinase in skeletal muscle, contractile activity emerges as a potent and physiologically relevant activator of MAP kinase signaling, and thus activation of this pathway is likely to be an important molecular mechanism by which skeletal muscle cells transduce mechanical and/or biochemical signals into downstream biological responses.

Effects of exercise and insulin on mitogen-activated protein kinase signaling pathways in rat skeletal muscle.

Studies in mammalian cells have established the existence of at least three distinct mitogen-activated protein kinase (MAP kinase) signaling pathways that are activated by a variety of growth factors and/or environmental stressors. We determined whether physical exercise, a physiological stressor, and insulin, a metabolic stimulator and growth factor, activate the c-jun NH2-terminus kinase (JNK), the p38 kinase, and/or the extracellular regulatory kinases (ERK; p42MAPK and p44MAPK) signaling pathways in rat skeletal muscle. Animals were studied immediately after running on a motorized treadmill for 10-60 min (20 m/min, 10% grade) or 5-30 min after an intraperitoneal injection of insulin (20 U/rat). Exercise increased skeletal muscle JNK activity by two- to threefold throughout the time course studied, whereas insulin did not significantly increase JNK activity. The p38 activity was slightly stimulated by exercise and not by insulin. The ERK kinase pathway, as assessed by ribosomal S6 kinase-2 activity assays and phosphospecific p42MAPK/p4NAPK immunoblotting, was stimulated by both exercise and insulin. These data are the first demonstration of exercise stimulating multiple intracellular signaling pathways in skeletal muscle. Activation of these MAP kinase signaling pathways may mediate changes in skeletal muscle growth and metabolism that occur in response to exercise.

Direct sequence analysis of human herpesvirus 6 (HHV-6) sequences from infants and comparison of HHV-6 sequences from mother/infant pairs.

Direct sequence analysis of polymerase chain reaction-amplified DNA fragments from the large tegument protein (LTP) gene of human herpesvirus 6 (HHV-6) was performed with use of uncultured peripheral blood mononuclear cells (PBMCs) from four mother/infant pairs. In two cases, LTP gene sequences were identical in paired mother/infant specimens, thus suggesting that mother-to-infant transmission of HHV-6 may have occurred. The genetic stability of HHV-6 strains was confirmed by the fact that there was no difference between amplified DNA fragments from sequential PBMC samples from two of two infants analyzed. In contrast, a change in the amplified viral strain was detected in an infant who had reinfection with HHV-6 variant B (HHV-6B). Furthermore, HHV-6B strains concurrently amplified from saliva and PBMCs from an adult were found to be different. The data suggest that HHV-6 may be frequently transmitted from mother-to-infant and that reinfection with HHV-6B may occur.