Distinct c-Met activation mechanisms induce cell rounding or invasion through pathways involving integrins, RhoA and HIP1

Abstract

Many carcinomas have acquired oncogenic mechanisms for activating c-Met, including c-Met overexpression and excessive autocrine or paracrine stimulation with hepatocyte growth factor (HGF). However, the biological outcome of c-Met activation through these distinct modes remains ambiguous. Here, we report that HGF-mediated c-Met stimulation triggers a mesenchymal-type collective cell invasion. By contrast, the overexpression of c-Met promotes cell rounding. Moreover, in a high-throughput siRNA screen that was performed using a library of siRNAs against putative regulators of integrin activity, we identified RhoA and the clathrin-adapter protein HIP1 as crucial c-Met effectors in these morphological changes. Transient RhoA activation was necessary for the HGF-induced invasion, whereas sustained RhoA activity regulated c-Met-induced cell rounding. In addition, c-Met-induced cell rounding correlated with the phosphorylation of filamin A and the downregulation of active cell-surface integrins. By contrast, a HIP1-mediated increase in β1-integrin turnover was required for the invasion triggered by HGF. Taken together, our results indicate that c-Met induces distinct cell morphology alterations depending on the stimulus that activates c-Met.

Integrin traffic – the update

“…Interestingly, PDGF has also been implicated in integrin endocytosis from CDRs, actin-dependent structures at the dorsal cell surface, by macropinocytosis (Gu et al, 2011), suggesting that context-dependent responses of integrins to growth factors exist. In another study, HGF has been shown to induce rapid β1 integrin endocytosis to drive protease- and integrin-dependent collective cell migration in 3D Matrigel in a process requiring clathrin, RhoA and the clathrin adaptor HIP1 (Mai et al, 2014). HIP1 in complex with the clathrin light-chain has also been shown to be necessary for the recycling of the endocytosed inactive integrin and to promote cell migration in fast-migrating lung cancer cells (Majeed et al, 2014).…”

“…However, it is clear that endosomal adaptors and scaffold proteins are key mediators of the coordinated traffic of these receptors and, interestingly, some of these adaptors, such as RCP or tensin-4, are upregulated in carcinomas (Muharram et al, 2014; Zhang et al, 2009). Furthermore, regulation of the activity of the Rho family of small GTPases, including Rac1 and RhoA, which are crucial downstream effectors of integrin signalling, has been linked to integrin traffic and is a key factor in determining cell shape, mobility and invasive capacity in many different cancer types (Jacquemet et al, 2013; Mai et al, 2014). Several studies have now established important regulatory steps in integrin traffic that determine whether the receptor is recycled or targeted for degradation.…”

“…Newly identified pathways include macropinocytosis from circular dorsal ruffles (CDRs) (Gu et al, 2011), F-actin-rich membrane projections on the apical cell surface, and a RhoA-dependent form of clathrin-mediated endocytosis (Mai et al, 2014), both triggered by growth factor receptor signalling. In addition, β1 integrin can be endocytosed via clathrin-independent carriers.…”

Thirty Years of Research on Met Receptor to Move a Biomarker from Bench to Bedside

“…Moreover, a new paradigm is emerging with the identification of distinct phenotypes elicited whether Met is activated via its overexpression or by the binding of its ligand (61). All these novel insights in Met action will probably lead to a better understanding of Met complex activity in cancers.…”

Paracrine Met signaling triggers epithelial–mesenchymal transition in mammary luminal progenitors, affecting their fate

“…However, in situ, mammary luminal cells do not express HGF, suggesting that Met signaling in mammary epithelial cells is activated in a paracrine manner. HGF-mediated paracrine and autocrine Met stimulation can trigger distinct biological responses in epithelial cells ( Mai et al, 2014 ). How Met-expressing luminal progenitors respond to the physiological paracrine action of HGF has not yet been investigated at the cellular and molecular levels.…”