Myoblast αvβ3 Integrin Levels Are Controlled by Transcriptional Regulation of Expression of the β3 Subunit and Down-regulation of β3 Subunit Expression Is Required for Skeletal Muscle Cell Differentiation

Abstract

The expression of alpha v beta3 integrin was examined in human skeletal muscle cells grown in vitro. The alpha v and beta3 subunits showed different patterns of expression during myogenesis. Expression of the alphav subunit did not change significantly during the growth and differentiation of muscle cells, whereas expression of the beta3 subunit was markedly down-regulated at both the message and protein levels. Down-regulation of beta3 subunit expression did not occur when cultures were treated with 5-bromo-2'-deoxyuridine to inhibit myoblast terminal differentiation, but did occur in cultures in which fusion was selectively inhibited by growth in EGTA-containing medium. These results suggest that the regulation of integrin beta3 subunit expression is tightly coupled to the myogenic terminal differentiation program, but is not simply a consequence of membrane reorganization due to the fusion process. Several stably transfected lines of mouse C2 myoblasts were derived from cultures transfected with a cDNA encoding the complete human beta3 integrin sequence under the control of the CMV promoter. Lines which constitutively expressed high levels of the human beta3 integrin subunit did not fuse or biochemically differentiate, whereas lines expressing moderate levels of the beta3 integrin subunit showed delayed fusion and differentiation. Lines expressing very low to undetectable levels of the human beta3 integrin subunit exhibited unimpaired fusion and differentiation. Taken together these results suggest (i) that down-regulation of alpha v beta3 integrin normally occurs as part of the myogenic terminal differentiation program, (ii) that this is mediated by regulation of the expression of the beta3 subunit, and (iii) that down-regulation of expression of the beta3 integrin subunit appears essential for myoblast differentiation.

ETS-1 converts endothelial cells to the angiogenic phenotype by inducing the expression of matrix metalloproteinases and integrin ?3

“…To our knowledge, the present study is the first to demonstrate that ETS-1 induces the expression of ␤ 3 subunit in ECs. It is thought that cell-surface appearance of integrin ␣ v ␤ 3 is preferentially regulated by the expression of the ␤ 3 subunit because the level of integrin ␣ v ␤3 in myoblasts was controlled by the expression of the ␤ 3 subunit (Blaschuk et al, 1997). Because integrin ␣ v ␤ 3 has been recognized as an important molecule in angiogenesis, the regulatory mechanism of the expression of ␣ v ␤ 3 has become an important issue.…”

Extracellular matrix remodeling accompanies axial muscle development and morphogenesis in the mouse

“…It is tempting to propose that when muscle cells become multinucleated, cell alignment for myocyte fusion is guided by the fibronectin matrix. Although a5b1, a4b1 and av integrins are not essential for myogenic cell fusion itself in vitro (Yang et al, 1996;Blaschuk et al, 1997;Taverna et al, 1998), cell engagement with the fibronectin matrix present within the myotome in vivo may serve to promote the approximation of myogenic cells, increasing the opportunities for fusion. The fact that b1D integrin knock-in and conditional b1 integrin knock-out mouse embryos show defects in myotube formation (Cachaço et al, 2003;Schwander et al, 2003) supports this hypothesis.…”

The influence of extracellular matrix derived from skeletal muscle tissue on the proliferation and differentiation of myogenic progenitor cells ex vivo

“…Proliferation of MPCs generates myoblasts that undergo several rounds of division before fusing to form myofibers, which comprise the basic cellular unit of skeletal muscle. During skeletal muscle regeneration, ECM molecules play a key role in the proliferation of MPCs and myoblasts as well as the subsequent stages of differentiation required to form new myofibers [11][12][13][14][15][16][17]. The study of skeletal muscle ECM regulation of MPC and myoblast behavior presents a significant challenge.…”