Signalling Pathways Regulating BC₃H1 Cell Myogenesis

Abstract

The myogenic cell line, BC₃H1, upon cell-to-cell contact or serum starvation differentiates as monitored by the appearance of muscle-specific markers, actin, myosin light chain 1 (MLC 1) and tropomyosin (Tm) and morphological changes. The detection of MLC 1 and five Tm isoforms in this cell line is novel. To assess the role of protein kinase C (pk C)-and protein kinase A (pk A) signal transduction pathways in controlling BC₃H1 cell differentiation, activators of pk C (TPA) and pk A (cAMP analogues, dibutyryl-cAMP and 8-Br-cAMP) were used. TPA (500nM) addition caused no deviation from the normal expression patterns of actin, Tm and MLC 1. Addition of cAMP analogues (500μM) delayed the appearance of MLC 1 and muscle-specific isoforms of Tm, as well as α-actin while β- and γ-actin levels remained unchanged. However, α-actin mRNA levels were not affected by cAMP analogues yet the typical β- and γ-actin mRNA downregulation was blocked. cAMP appears to be operating at multiple levels to regulate BC₃H1 cell myogenesis such as post-transcriptional and translational. In addition, given the similarity in mechanisms through which cAMP and adenovirus early region 1A (AdE1A) mediate gene activation, the effect of AdE1A on BC₃H1 cell differentiation was investigated. A stable transfected AdE1A clonal cell line, BC₃E7, was characterized. Together with altered morphology, BC₃E7 cells failed to show the characteristic expression of muscle-specific markers actin, Tm and MLC 1. AdE1A transfection disrupted the synchronous expression of muscle-specific proteins during BC₃H1 cell differentiation.