PDK1 regulates focal adhesion disassembly through modulation of αvβ3 integrin endocytosis

Abstract

BSTRACTNon-amoeboid cell migration is characterised by dynamic competition among multiple protrusions to establish new adhesion sites at the cell's leading edge. However, the mechanisms that regulate the decision to disassemble or to grow nascent adhesions are not fully understood. Here we show that, in endothelial cells, 3-phosphoinositide-dependent protein kinase 1 (PDK1) promotes focal adhesion (FA) turnover by controlling endocytosis of integrin avb3 in a PI3K-dependent manner. We demonstrate that PDK1 binds and phosphorylates integrin avb3. Downregulation of PDK1 increases FA size and slows down their disassembly. This process requires both PDK1 kinase activity and PI3K activation but does not involve Akt. Moreover, PDK1 silencing stabilises FA in membrane protrusions decreasing migration of endothelial cells on vitronectin. These results indicate that modulation of integrin endocytosis by PDK1 hampers endothelial cell adhesion and migration on extracellular matrix, thus unveiling a novel role for this kinase.

PDK1: A signaling hub for cell migration and tumor invasion

“…While the activation of PDK1 by PI3K appears to be the widespread mechanism explaining PDK1 role in cell migration, the downstream effectors transducing PDK1 signaling are rather uncertain. PDK1 was proved to regulate cell migration by acting through Akt [12], MRCKα [14], ROCK1 [44], PAK1 [15], PLCγ1 [45] and β3 integrin [43]. A possible explanation of the variety of PDK1 downstream effectors in the regulation of cell migration resides in the variety of migration strategies that cells might adopt.…”

“…Besides the kinase activity, β3 integrin endocytosis and FA dynamics require the upstream activation of PI3K and PDK1 binding to PtdIns(3,4,5)P3. Thus, by regulating β3 endocytosis and FA dynamics, PDK1 modulates endothelial cells migration ability [43] (Fig. 3A).…”

“…PDK1 is able to phosphorylate other proteins not belonging to AGC kinase family, such as β3 integrin [42,43]. Moreover, PDK1 is able to bind and activate in a kinase independent manner some proteins belonging to AGC kinase family, such as ROCK1 [44] and MRCKα [14], or proteins not belonging to this family, such as PLCγ1 [45].…”

“…Recently, it was shown that PDK1 regulates β3 integrin endocytosis by phosphorylating its cytoplasmic tail [43].…”

“…Interestingly, when PDK1 is down-regulated in endothelial cells, the process of FA disassembly is compromised and FA enlarge and increase in number [43]. This phenotype is the result of the altered endocytosis of integrin αvβ3.…”