Calcium-stimulated disassembly of focal adhesions mediated by an ORP3/IQSec1 complex

Abstract

Coordinated assembly and disassembly of integrin-mediated focal adhesions (FAs) is essential for cell migration. Many studies have shown that FA disassembly requires Ca2+ influx, however our understanding of this process remains incomplete. Here, we show that Ca2+ influx via STIM1/Orai1 calcium channels, which cluster near FAs, leads to activation of the GTPase Arf5 via the Ca2+-activated GEF IQSec1, and that both IQSec1 and Arf5 activation are essential for adhesion disassembly. We further show that IQSec1 forms a complex with the lipid transfer protein ORP3, and that Ca2+ influx triggers PKC-dependent translocation of this complex to ER/plasma membrane (PM) contact sites adjacent to FAs. In addition to allosterically activating IQSec1, ORP3 also extracts PI4P from the PM, in exchange for phosphatidylcholine. ORP3-mediated lipid exchange is also important for FA turnover. Together, these findings identify a new pathway that links calcium influx to FA turnover during cell migration.

Lipid Exchangers: Cellular Functions and Mechanistic Links With Phosphoinositide Metabolism

“…It is unclear how this relates to reports showing that ORP3 recruits R-Ras, a small G protein that is also involved in cell adhesion and migration (Lehto et al, 2008;Weber-Boyvat et al, 2015a). Likewise, it is unknown whether the cellular function of ORP3 relies on its ability to downregulate PM PI(4)P levels and, maybe, to mediate PC/PI(4)P exchange (D'Souza et al, 2020;Gulyás et al, 2020).…”

“…However, some ORP/Osh proteins have a dual ability to recognize sterol and PI(4)P or PS and PI(4)P and observations suggest that they exchange these lipids in the cell. A recent report suggests that ORP3 acts as a PC/PI(4)P exchanger (D'Souza et al, 2020). Other proteins are associated with a more complex picture.…”

“…ORP3 is the best characterized member of subfamily III. It contains a PI(4)P/PI(4,5)P 2 -specific PH domain to associate with the PM (Gulyás et al, 2020), a canonical and non-canonical FFAT motif (Loewen et al, 2003;Weber-Boyvat et al, 2015a) and a C-terminal ORD that was recently shown to capture PI(4)P or PC, but neither PS nor sterol (D'Souza et al, 2020;Gulyás et al, 2020). ORP3 relocates to ER-PM contact sites upon phosphorylation by PKC following PMA treatment or agonist stimulation (Lehto et al, 2008;Weber-Boyvat et al, 2015a;Gulyás et al, 2020), a process that is synergized by an elevation of intracellular Ca 2+ through store-operated calcium entry (SOCE) by the STIM/Orai1 complex.…”

“…ORP3 activation by PKC and Ca 2+ entry is linked to a mechanism implicated in focal adhesion dynamics. Once recruited to ER-PM contact sites, ORP3 interacts with IQSec1, a guanine nucleotide exchange factor of Arf5 to trigger focal adhesion disassembly (D'Souza et al, 2020). It is proposed that this process, associating STIM/Orai1, ORP3 and IQSec1/Arf5 occurs at the rear-front of cells to guarantee their migration (Machaca, 2020).…”

Thermal proteome profiling reveals distinct target selectivity for differentially oxidized oxysterols

“…The most stabilized protein was Paxillin (PXN), an autophagy substrate that interacts with LC3 during focal adhesion (FAs) disassembly in highly metastatic tumor cells. [40] FA turnover is reportedly influenced by ORP3-mediated lipid exchange, [41] which may explain the association of oxysterols with PXN. A significantly destabilized target was the microtubule-associated protein 1S (MAP1S), whose deficiency causes impaired autophagic degradation of lipid droplets, which then accumulate in normal renal epithelial cells, initiating the development of renal cell carcinomas.…”