β1 integrin–dependent Rac/group I PAK signaling mediates YAP activation of Yes-associated protein 1 (YAP1) via NF2/merlin

Abstract

Cell adhesion to the extracellular matrix or to surrounding cells plays a key role in cell proliferation and differentiation and is critical for proper tissue homeostasis. An important pathway in adhesion-dependent cell proliferation is the Hippo signaling cascade, which is coregulated by the transcription factors Yes-associated protein 1 (YAP1) and transcriptional coactivator with PDZ-binding motif (TAZ). However, how cells integrate extracellular information at the molecular level to regulate YAP1's nuclear localization is still puzzling. Herein, we investigated the role of β1 integrins in regulating this process. We found that β1 integrin-dependent cell adhesion is critical for supporting cell proliferation in mesenchymal cells both and β1 integrin-dependent cell adhesion relied on the relocation of YAP1 to the nucleus after the down-regulation of its phosphorylated state mediated by large tumor suppressor gene 1 and 2 (LATS1/2). We also found that this phenotype relies on β1 integrin-dependent local activation of the small GTPase RAC1 at the plasma membrane to control the activity of P21 (RAC1)-activated kinase (PAK) of group 1. We further report that the regulatory protein merlin (neurofibromin 2, NF2) interacts with both YAP1 and LATS1/2 via its C-terminal moiety and FERM domain, respectively. PAK1-mediated merlin phosphorylation on Ser-518 reduced merlin's interactions with both LATS1/2 and YAP1, resulting in YAP1 dephosphorylation and nuclear shuttling. Our results highlight RAC/PAK1 as major players in YAP1 regulation triggered by cell adhesion.

Identification of Gli1‐interacting proteins during simvastatin‐stimulated osteogenic differentiation of bone marrow mesenchymal stem cells

“…RAC/PAK1 is a major regulator of YAP1, a crucial molecule in Hippo signaling that plays key roles in cell proliferation, differentiation, and apoptosis . Silencing of PSMC2 in osteosarcoma cell lines significantly suppressed cell proliferation, enhanced apoptosis, and accelerated G2/M phase and/or S‐phase arrest .…”

The role of Hippo signaling pathway and mechanotransduction in tuning embryoid body formation and differentiation

“…Integrins play a crucial role in mediating the signaling from ECM, and multiple connections are identified between integrins and YAP activity. Integrin‐linked kinase can inhibit the Merlin activation by inhibiting phosphatase MYPT1 or through activating RAC and PAK (Sabra et al, 2017; Serrano, McDonald, Lock, Muller, & Dedhar, 2013). Furthermore, it is found (Chakraborty et al, 2017) that the integrin‐mediated regulation of Hippo signaling is linked to focal adhesion kinase (FAK).…”

“…Moreover, the past memory of ESC/iPSCs and methods of EB formation, as well as external and internal signals could affect the differentiation and the fate of EBs (Boraas, Guidry, Pineda, & Ahsan, 2016; Vining & Mooney, 2017). Recently, alternative methods of EB formation have been developed that allow for highly accurate control of EBs size, shape, and external biochemical and biomechanical signals, resulting in reproducibly produced homogeneous EBs with the simulation of cell signaling pathways (Sabra et al, 2017; Sato, Idiris, Miwa, & Kumagai, 2016; Son et al, 2017). Now, a fundamental question arises regarding whether the size of EBs, uniformity, and topological microstructure are determined by accidentally spherical agglomerated cells or the cell aggregate under a programmed process and elaborate molecular mechanism.…”

Integrin-dependent YAP signaling requires LAMTOR1 mediated delivery of Src to the plasma membrane

“…However, how the mechanical cues embedded within the extracellular matrix are translated into a functional regulation of YAP and TAZ nuclear shuttling remains elusive. We and others have identified that integrin-dependent cell adhesion and in particular β1 integrins are of critical importance for YAP/TAZ nuclear shuttling [13,14]. Indeed, β1 integrin dependent cell adhesion-signaling, likely through the Src family kinases, leads to the recruitment and activation of Rac-1 at protrusive cell borders, and stimulates a PAK1 dependent signaling cascade resulting in merlin phosphorylation.…”