Further Investigation of Some Inhibitors on Myogenic Differentiation: Mechanism of Inhibition with HMBA on Quail Myoblasts Transformed with Rous Sarcoma Virus

Abstract

To investigate the mechanism of myogenic differentiation, we are using quail myoblast cells (QM cells) transformed with a temperature-sensitive mutant of Rous sarcoma virus (ts-RSV), termed QM-RSV cells. At 35.5°C, a permissive temperature for RSV, QM-RSV cells repeatedly proliferate without differentiation, but, at 41°C, a nonpermissive temperature, myogenic differentiation proceeds. This temperature dependency of the differentiation is derived from protein kinase activity of pp60^v-src, as tyrosine dephosphorylation is necessary for myogenic differentiation of QM-RSV cells. In this study, it was demonstrated that among four fusion inhibitors, aspirin, doxorubicin, HMBA and TPA, three of the inhibitors, except for TPA, inhibited inyogenin gene expression. Moreover, HMBA inhibited myoblast fusion accompanying inhibition of tyrosine dephosphorylation of certain proteins, and recovered the tyrosine kinase activity of pp60^v-src to a certain extent. To study the effect of HMBA on the intracellular localization of pp60^v-src, detergent-soluble and detergent-resistant fractions were prepared with Triton X-100. As a result, it was shown that pp60^v-src mainly exists in detergent-resistant fraction at 35.5°C. While almost all of the pp60^v-src at 41°C exists in detergent-soluble fraction. HMBA treatment retained pp60^v-src in detergent-resistant fraction even at 41°C. These results suggest that HMBA inhibits myogenic differentiation of QM-RSV cells by affecting the regulation of pp60^v-src.