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This Article Full Text Full Text (PDF) All Versions of this Article: 297/4/C1012    most recent 00567.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Scholz, M. E. Articles by Kubis, H.-P. PubMed PubMed Citation Articles by Scholz, M. E. Articles by Kubis, H.-P.

MUSCLE CELL BIOLOGY AND CELL MOTILITY

Different roles of H-ras for regulation of myosin heavy chain promoters in satellite cell-derived muscle cell culture during proliferation and differentiation

¹Department of Physiology, Hannover Medical School, Hannover, Germany; ²Department of Biochemistry, Hannover Medical School, Hannover, Germany; ³Department of Medicine, University of Alabama, Birmingham, Alabama; and ⁴School of Veterinary Medicine and Science, University of Nottingham, Sutton Bonington, United Kingdom

Submitted 5 November 2008 ; accepted in final form 21 July 2009

The effect of constitutively activated proto-oncogene H-ras (H-rasQ61L) on the regulation of myosin heavy chain (MHC) promoter activities was investigated in rabbit satellite cell-derived muscle cell culture during the proliferation stage and early and later stages of differentiation, respectively. During proliferation, overexpression of H-rasQ61L did not affect basal level of activity of the slow MHCI/β or the fast MHCIId/x promoter luciferase reporter gene construct in transient transfection assays. By contrast, H-rasQ61L affected both MHC promoter activities during differentiation, and this effect changes from inactivation after 2 days to activation after 4 days of differentiation. The activating effect of H-rasQ61L on both MHC promoters after 4 days of differentiation was significantly reduced by LY-294002, a specific inhibitor of the phosphoinositol-3-kinase (PI3K), a downstream target of Ras. Furthermore, the protein kinase Akt (protein kinase B), a downstream target of PI3k, was activated 4 days after initiation of differentiation in myotubes overexpressing H-rasQ61L. By contrast, inhibition of another Ras downstream pathway, mitogen-activated protein kinase kinase 1/2-extracellular signal-regulated protein kinase 1/2 (MKK1/2-ERK1/2-MAPK), increased activities of both MHC promoters, indicating a suppressive role of this pathway. Moreover, the Ras-PI3K-Akt signaling pathway is involved in the activation of MHCI/β and IId/x promoters in a later stage of differentiation of muscle cells, presumably by a known inhibiting effect of activated Akt on the MKK1/2-ERK1/2-MAPK pathway. The experiments demonstrate that during differentiation of muscle cells activated H-ras is an important regulator of MHC isoform promoter function with opposite effects during early and later stages.

extracellular signal regulated protein kinase 1/2; mitogen-activated protein kinase; phosphosinositol-3-kinase; Akt; mammalian target of rapamycin