title: Insulin receptor substrate protein 53kDa (IRSp53) is a negative regulator of myogenic differentiation.
abstract: Fusion of mononucleated myoblasts to generate multinucleated myotubes is a critical step in skeletal muscle development. Filopodia, the actin cytoskeleton based membrane protrusions, have been observed early during myoblast fusion, indicating that they could play a direct role in myogenic differentiation. The control of filopodia formation in myoblasts remains poorly understood. Here we show that the expression of IRSp53 (Insulin Receptor Substrate protein 53kDa), a known regulator of filopodia formation, is down-regulated during differentiation of both mouse primary myoblasts and a mouse myoblast cell line C2C12. Over-expression of IRSp53 in C2C12 cells led to induction of filopodia and decrease in cell adhesion, concomitantly with inhibition of myogenic differentiation. In contrast, knocking down the IRSp53 expression in C2C12 cells led to a small but significant increase in myotube development. The decreased cell adhesion of C2C12 cells over-expressing IRSp53 is correlated with a reduction in the number of vinculin patches in these cells. Mutations in the conserved IMD domain (IRSp53 and MIM (missing in metastasis) homology domain) or SH3 domain of IRSp53 abolished the ability of this protein to inhibit myogenic differentiation and reduce cell adhesion. Over-expression of the IMD domain alone was sufficient to decrease the cell-extracellular matrix adhesion and to inhibit myogenesis in a manner dependent on its function in membrane shaping. Based on our data, we propose that IRSp53 is a negative regulator of myogenic differentiation which correlates with the observed down regulation of IRSp53 expression during myoblast differentiation to myotubes.
authors.affiliation: School of Biological Sciences, Nanyang Technological University, Singapore 637551, Republic of Singapore.
authors.forename: Ashish
authors.initials: A
authors.lastname: Misra
authors.forename: Bhawana
authors.initials: B
authors.lastname: George
authors.forename: Rajamuthiah
authors.initials: R
authors.lastname: Rajmohan
authors.forename: Neeraj
authors.initials: N
authors.lastname: Jain
authors.forename: Ming Hwa
authors.initials: MH
authors.lastname: Wong
authors.forename: Ravi
authors.initials: R
authors.lastname: Kambadur
authors.forename: Thirumaran
authors.initials: T
authors.lastname: Thanabalu
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D002460:Cell Line; D005455:Fluorescent Antibody Technique; D006801:Humans; D051379:Mice; D032446:Myoblasts / Q000166:cytology*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000502:physiology*; D018909:src Homology Domains
chemical_list: C539986:Baiap2 protein, mouse; D009419:Nerve Tissue Proteins