Smads, Tak1, and Their Common Target Atf-2 Play a Critical Role in Cardiomyocyte Differentiation

Abstract

We previously demonstrated that bone morphogenetic proteins (BMPs) induce cardiomyocyte differentiation through the mitogen-activated protein kinase kinase kinase TAK1. Transcription factors Smads mediate transforming growth factor-β signaling and the ATF/CREB family transcription factor ATF-2 has recently been shown to act as a common target of the Smad and the TAK1 pathways. We here examined the role of Smads and ATF-2 in cardiomyocyte differentiation of P19CL6, a clonal derivative of murine P19 cells. Although P19CL6 efficiently differentiates into cardiomyocytes when treated with dimethyl sulfoxide, P19CL6noggin, a P19CL6 cell line constitutively overexpressing the BMP antagonist noggin, did not differentiate into cardiomyocytes. Cooverexpression of Smad1, a ligand-specific Smad, and Smad4, a common Smad, restored the ability of P19CL6noggin to differentiate into cardiomyocytes, whereas stable overexpression of Smad6, an inhibitory Smad, completely blocked differentiation of P19CL6, suggesting that the Smad pathway is necessary for cardiomyocyte differentiation. ATF-2 stimulated the βMHC promoter activity by the synergistic manner with Smad1/4 and TAK1 and promoted terminal cardiomyocyte differentiation of P19CL6noggin, whereas overexpression of the dominant negative form of ATF-2 reduced the promoter activities of several cardiac-specific genes and inhibited differentiation of P19CL6. These results suggest that Smads, TAK1, and their common target ATF-2 cooperatively play a critical role in cardiomyocyte differentiation.

Transforming Growth Factor-β-activated Kinase-1 (TAK1), a MAP3K, Interacts with Smad Proteins and Interferes with Osteogenesis in Murine Mesenchymal Progenitors

“…Only one study has demonstrated that in vitro immunoprecipitated TAK1 was able to phosphorylate exogenously added MEKK6 in a BMP2-dependent manner (21). Neverthe- less, overexpression of TAK1 has been shown to mimic the effects of BMP, for example in differentiation of P19 embryonic teratoma cells into cardiomyocytes (17) and patterning of the early Xenopus embryo (18). These data led to the suggestion that TAK1 synergizes with Smads to mediate TGF-␤/BMP responses, but a direct effect of this MAPKKK on the specific activities of Smads was not addressed in those studies.…”

“…For instance, Smad and TAK1 pathways integrate ATF-2 as a common nuclear target in cells stimulated with TGF-␤ (16). TAK1 was reported to restore the ability of P19CL6[noggin] cells to differentiate into cardiac myocytes mimicking the effect of BMP2 upon these cells, whereas forced expression of a dominant-negative form of TAK1 interfered with this induced differentiation (17). TAK1 (co-expressed with its activator protein TAB1) has been proposed to synergize with Smads and to induce ventral mesoderm formation in Xenopus embryos, thereby mimicking BMP activity.…”

p38MAPK Acts in the BMP7-dependent Stimulatory Pathway during Epithelial Cell Morphogenesis and Is Regulated by Smad1

“…*, p Ͻ 0.05. n ϭ 3 independent experiments. ation (30). A study of peroxisome proliferator-activated receptor-␥ regulation during adipogenesis shows that both BMP2 and p38 MAPK act cooperatively during the differentiation of undifferentiated mesenchymal cells into adipocytes.…”

Ecsit-ement on the crossroads of Toll and BMP signal transduction: Figure 1.

“…In fact, TAK1 and its regulatory adaptor TAB1 were originally discovered as a TGF-␤-activated kinase complex (Shibuya et al 1996(Shibuya et al , 1998, and their contribution to TGF-␤ signal transduction together with JNK and p38 MAPKs is thought to constitute a so called Smad-independent signaling module. However, recent evidence suggests a possible bridging between Smads (including inhibitory Smads) and kinases such as TAK1 or p38 MAPK, which can either physically or functionally interact to mediate diverse physiological responses such as apoptosis or cell differentiation (Kimura et al 2000;Monzen et al 2001;Yanagisawa et al 2001;Arsura et al 2003;Edlund et al 2003). Ecsit now brings a new dimension to the complex interactions of signaling components downstream of TGF-␤ superfamily receptors.…”