Myogenic signaling by lithium in cardiomyoblasts is Akt independent but requires activation of the beta-catenin-Tcf/Lef pathway.
Rat H9c2 cardiomyoblasts can proliferate and maintain an undifferentiated state in the presence of serum. These cardiomyoblasts have been used as a cellular model to study myogenic differentiation after serum withdrawal. Here, we examined the effects of lithium, a known inhibitor of glycogen synthase kinase-3beta and activator of Wnt pathway in myogenic differentiation. We show that in the presence of serum, lithium induced the differentiation of H9c2 cells as measured by multinucleated myotube formation and expression of the muscle-specific proteins, myogenin and skeletal alpha-actin. This differentiation was preceded by nuclear accumulation of beta-catenin, which was associated with increased Tcf/Lef-dependent transcription. We also observed that lithium mediated the activation of phosphatidylinositol 3-kinase (PI3-kinase) and its downstream target Akt. Inhibition of PI3-kinase by LY294002 and over-expression of dominant-negative PI3-kinase caused a marked reduction in beta-catenin levels. This inhibition was associated with decreased beta-catenin-Tcf/Lef-dependent transcription, lack of multinucleated myotube formation, and expression of the muscle-specific proteins. In contrast, expression of dominant-negative Akt failed to inhibit the effects of lithium. We conclude that the capacity of lithium to overcome the inhibitory effects of serum and to induce the differentiation of H9c2 cardiomyoblasts is mediated, in part, by the stabilization and nuclear translocation of beta-catenin in a PI3-kinase-dependent but Akt-independent manner. Once activated, beta-catenin then interacts with the Lef/Tcf complex to regulate expression of myogenic-inducing genes.
Kashour
Tarek
T
Section of Cardiology, St. Boniface General Hospital, Winnipeg, Man., Canada R2H 2A6.
Burton
Teralee
T
Dibrov
Alexander
A
Amara
Francis
F
D000818:Animals; D002417:Cattle; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D002470:Cell Survival; D002867:Chromones / Q000494:pharmacology; D003598:Cytoskeletal Proteins / Q000096:biosynthesis*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005799:Genes, Dominant; D008094:Lithium / Q000494:pharmacology*; D009025:Morpholines / Q000494:pharmacology; D032383:Myocytes, Cardiac / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D012710:Serum Albumin, Bovine / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D015534:Trans-Activators / Q000096:biosynthesis*; D014157:Transcription Factors / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects*; D051176:beta Catenin
D002867:Chromones; D003598:Cytoskeletal Proteins; D004791:Enzyme Inhibitors; D008094:Lithium; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D012710:Serum Albumin, Bovine; D015534:Trans-Activators; D014157:Transcription Factors; D051176:beta Catenin; C495268:Ctnnb1 protein, rat; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C494920:Akt1 protein, rat