Integrin Alpha Subunit Ratios, Cytoplasmic Domains, and Growth Factor Synergy Regulate Muscle Proliferation, Differentiation, and Signaling

Integrin function in muscle differentiation was addressed by ectopic expression of integrin alpha subunits in primary quail skeletal muscle. Ectopic expression of either the human or α5 or the chicken α6 subunit produced contrasting phenotypes. The α5 transfected myoblasts remain in the proliferative phase and are differentiation inhibited. Myoblasts overexpressing the α6 subunit exhibit inhibited proliferation and substantial differentiation. Antisense suppression of endogenous quail α6 inhibits myoblast differentiation and promotes proliferation. These effects of ectopic α subunits are mediated by the cytoplasmic domains. Ectopic expression of chimeric alpha subunits, α5ex/6cyto and α6ex/5cyto, produced phenotypes opposite to those observed with ectopic α5 or α6 expression. Myoblasts that express α5ex/6cyto show decreased proliferation and increased differentiation. The α6ex/5cyto transfectants remain in the proliferative phase unless confluent. Expression of human α5 subunit cytoplasmic domain truncations, localizes the active site to the conserved GFFKR motif. Ectopic α5 and α6 expression also results in contrasting responses to the mitogenic effects of serum growth factors. Myoblasts expressing the human α5 subunit differentiate in the absence of serum while differentiation of untransfected and α6 transfected myoblasts is insensitive to serum concentration. Addition of individual, exogenous growth factors to α5 transfected myoblasts results in unique responses that differ from their effects on untransfected cells. bFGF or TGFβ inhibit the serum-free differentiation of α5 transfected myoblasts. bFGF stimulates proliferation whereas TGF-β inhibits it. Insulin or TGF-α promote proliferation and differentiation; insulin alters myotube morphology. TGF-α or PDGF-BB enhance muscle α-actinin organization into myofibrils. bFGF and insulin promote survival of α5 transfected myoblasts in serum-free medium. TGF-α and TGF-β promote survival of untransfected myoblasts. Our observations demonstrate: (1) a specificity for integrin α subunits in regulating myoblast proliferation and differentiation, (2) that the ratio of integrin expression can affect the decision to proliferate or differentiate, (3) a role for the α subunit cytoplasmic domain in mediating proliferative and differentiative signals, (4) regulation of proliferation, differentiation, cytoskeletal assembly, and cell survival depends on the expression levels of different integrins and the growth factor environment in which the cells reside.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Biochemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Sastry, Sarita Kandula

Contributors dc:contributor

• Horwitz, Alan F.

• Biology, Cell

Language dc:language

eng

Identifier

(MiAaPQ)AAI9717332

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/84879