Institute for Chemistry and Biochemistry, Freie Universität Βerlin, 14195 Berlin, Germany.
BMC Biol. 2014 May 30;12:43. doi: 10.1186/1741-7007-12-43.
BMP-induced chemotaxis of mesenchymal progenitors is fundamental for vertebrate development, disease and tissue repair. BMP2 induces Smad and non-Smad signalling. Whereas signal transduction via Smads lead to transcriptional responses, non-Smad signalling induces both, transcriptional and immediate/early non-transcriptional responses. However, the molecular mechanisms by which BMP2 facilitates planar cell polarity, cortical actin rearrangements, lamellipodia formation and chemotaxis of mesenchymal progenitors are poorly understood. Our aim was to uncover the molecular mechanism by which BMP2 facilitates chemotaxis via the BMP2-dependent activation of PI3K and spatiotemporal control of PIP3 production important for actin rearrangements at the mesenchymal cell cytocortex.
We unveiled the molecular mechanism by which BMP2 induces non-Smad signalling by PI3K and the role of the second messenger PIP3 in BMP2-induced planar cell polarity, cortical actin reorganisation and lamellipodia formation. By using protein interaction studies, we identified the class Ia PI3K regulatory subunit p55γ to act as a specific and non-redundant binding partner for BMP receptor type II (BMPRII) in concert with the catalytic subunit p110α. We mapped the PI3K interaction to a region within the BMPRII kinase. Either BMP2 stimulation or increasing amounts of BMPRI facilitated p55γ association with BMPRII, but BMPRII kinase activity was not required for the interaction. We visualised BMP2-dependent PIP3 production via PI3K p55γ/p110α and were able to localise PIP3 to the leading edge of intact cells during the process of BMP2-induced planar cell polarity and actin dependent lamellipodia formation. Using mass spectrometry, we found the highly PIP3-sensitive PH-domain protein LL5β to act as a novel BMP2 effector in orchestrating cortical actin rearrangements. By use of live cell imaging we found that knock-down of p55γ or LL5β or pharmacological inhibition of PI3K impaired BMP2-induced migratory responses.
Our results provide evidence for an important contribution of the BMP2-PI3K (p55γ/p110α)- PIP3-LL5β signalling axis in mesenchymal progenitor cell chemotaxis. We demonstrate molecular insights into BMP2-induced PI3K signalling on the level of actin reorganisation at the leading edge cytocortex. These findings are important to better understand BMP2-induced cytoskeletal reorganisation and chemotaxis of mesenchymal progenitors in different physiological or pathophysiological contexts.
BMP 诱导间充质祖细胞的趋化作用对于脊椎动物的发育、疾病和组织修复至关重要。BMP2 诱导 Smad 和非 Smad 信号转导。虽然 Smad 信号转导导致转录反应，但非 Smad 信号转导诱导转录和即时/早期非转录反应。然而，BMP2 促进平面细胞极性、皮质肌动蛋白重排、片状伪足形成和间充质祖细胞趋化作用的分子机制知之甚少。我们的目标是揭示 BMP2 通过依赖于 BMP2 的 PI3K 激活和 PIP3 产生的时空控制促进趋化作用的分子机制，这对于间充质细胞质皮质的肌动蛋白重排很重要。
我们揭示了 BMP2 通过 PI3K 诱导非 Smad 信号转导的分子机制，以及第二信使 PIP3 在 BMP2 诱导的平面细胞极性、皮质肌动蛋白重排和片状伪足形成中的作用。通过蛋白质相互作用研究，我们确定了 I 类 PI3K 调节亚基 p55γ 作为 BMP 受体 II 型（BMPRII）的特异性和非冗余结合伙伴，与催化亚基 p110α 一起。我们将 PI3K 相互作用映射到 BMPRII 激酶的一个区域。BMP2 刺激或增加的 BMPRI 促进 p55γ 与 BMPRII 的结合，但 BMPRII 激酶活性不是相互作用所必需的。我们通过 PI3K p55γ/p110α 可视化 BMP2 依赖性 PIP3 产生，并能够在 BMP2 诱导的平面细胞极性和肌动蛋白依赖性片状伪足形成过程中定位 PIP3 到完整细胞的前缘。使用质谱法，我们发现高度敏感 PIP3 的 PH 结构域蛋白 LL5β 作为一种新型 BMP2 效应物，在协调皮质肌动蛋白重排中起作用。通过使用活细胞成像，我们发现 p55γ 或 LL5β 的敲低或 PI3K 的药理学抑制会损害 BMP2 诱导的迁移反应。
我们的研究结果为 BMP2-PI3K（p55γ/p110α）-PIP3-LL5β 信号轴在间充质祖细胞趋化作用中的重要作用提供了证据。我们证明了 BMP2 诱导的 PI3K 信号在质膜前缘皮质肌动蛋白重排水平上的分子见解。这些发现对于更好地理解不同生理或病理生理条件下 BMP2 诱导的细胞骨架重排和间充质祖细胞趋化作用非常重要。
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