BMP2-induced chemotaxis requires PI3K p55γ/p110α-dependent phosphatidylinositol (3,4,5)-triphosphate production and LL5β recruitment at the cytocortex

Abstract

BackgroundBMP-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.ResultsWe 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.ConclusionsOur 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.

Role of bone morphogenetic proteins in sprouting angiogenesis: differential BMP receptor‐dependent signaling pathways balance stalkvs. tip cell competence

“…Whereas the sprout migrates collectively, tip cells constantly scan the environment, sensing gradients of chemoattractants to determine the direction of migration (4). To test whether BMP2 or BMP6 act as endothelial chemoattractants, we used a 2-dimensional assay that allows chemotaxis analysis in a gradient-and time-resolved manner (22). In the presence of a growth factor gradient, chemotaxis occurred during a 16-h observation period, whereas in the absence of a gradient, we observed only random motion (chemokinesis; Fig.…”

“…These promote transcriptional and nontranscriptional responses, the latter including actin reorganization and cell migration (17, 20). Among these non-SMAD pathways are the p38 (MAPK; hereafter referred to as p38) and PI3K pathways (21, 22). …”

Bone morphogenetic protein signaling in vertebrate motor neurons and neuromuscular communication

“…On the other hand, it may activate local BMP-dependent pathways involved in the disassembly of AChR clusters at the NMJ (Figure 2B ). Remarkably, this notion is supported by recent evidence showing that the BMP-2 induced chemotaxis of mesenchymal progenitor cells depends on the effect of LL5β, likely mediated by the BMPRII, on cortical actin rearrangements (Hiepen et al, 2014 ).…”

“…Different studies have shown that Smad-independent BMP induced pathways are related to local signals that involve cytoskeleton arrangements. In this regard, BMP-mediated cell migration, axon and dendrite growth, or axon guidance require activation of the small GTPase Cdc42, PI3-K, p38 MAPK, c-Jun N-terminal kinase (JNKs) or LIMK (Foletta et al, 2003 ; Lee-Hoeflich et al, 2004 ; Eaton and Davis, 2005 ; Wen et al, 2007 ; Gamell et al, 2008 , 2011 ; Podkowa et al, 2010 ; Hiepen et al, 2014 ). Interestingly, BMPRII has been involved in most of the studies localizing or coordinating this local signaling.…”

“…For instance, upon BMP-2 stimulation, the p38 downstream effector Hsp25, that regulates cytoskeletal dynamics, colocalizes with BMPRII (Gamell et al, 2011 ). In addition, BMP-2 induced planar cell polarity and actin dependent lamellipodia formation mediated by PI3-K involve the binding of the PI3K regulatory subunit p55γ to BMPRII, irrespective of the presence of the C-terminal tail (Hiepen et al, 2014 ). Also, BMPRII lacking the C-terminal tail is able to activate Smad pathways in response to BMP-2 (Nohe et al, 2002 ), suggesting that this domain of BMPRII could play other regulatory roles.…”