The ESCRT machinery mediates polarization of fibroblasts through regulation of myosin light chain

Abstract

SummaryRecent evidence implicates the endosomal sorting complex required for transport (ESCRT) in the regulation of epithelial polarity in Drosophila melanogaster, but the mechanisms responsible for this action remain unclear. Here we show that ESCRTs determine cell orientation during directed migration in human fibroblasts. We find that endosomal retention of a5b1 integrin and its downstream signaling effector Src in ESCRT-depleted cells is accompanied by the failure to activate myosin light chain kinase (MLCK), which thereby cannot phosphorylate myosin regulatory light chain (MRLC). Using this mechanism, ESCRT-depleted fibroblasts fail to orient their Golgi complex to undergo directional migration and show impaired focal adhesion turnover and increased spreading on fibronectin. Consistent with these findings, expression of a phosphomimetic mutant of MRLC in ESCRT-depleted cells restores normal phenotypes during cell spreading and orientation of the Golgi. These results suggest that, through their role in regulating integrin trafficking, ESCRTs regulate phosphorylation of MRLC and, subsequently, Golgi orientation and cell spreading.

The Endosomal Sorting Complex Required for Transport Pathway Mediates Chemokine Receptor CXCR4-promoted Lysosomal Degradation of the Mammalian Target of Rapamycin Antagonist DEPTOR

“…The role of ESCRTs on cell survival remains to be examined further, but it is also possible that ESCRTs have other roles. ESCRTs have been linked to cell polarity and controlling focal adhesion dynamics (79,80). Akt signaling has been linked to CXCR4-induced directed migration of HeLa cells (81), and directed cell migration is an important developmental and pathophysiological function of CXCR4 (3,4,6,48,82).…”

Integrin traffic – the update

“…Consequently, the net endocytosis rate of active β1 integrin is relatively high compared to its inactive conformer and, therefore, in the steady-state situation, inactive β1 is mostly localized at the plasma membrane, whereas active β1 integrin appears to be more cytoplasmic. This localisation is most likely linked to the observation that ligand-bound active integrins traffic to late endosomes and lysosomes, either for degradation (Lobert and Stenmark, 2012) or for ligand detachment, in an increasingly acidic environment, to allow recycling of unbound free integrins back to the plasma membrane. In line with this, active β1 integrin appears to recycle slowly (possibly owing to the requirement for ligand dissociation prior to recycling) and the active, but not the inactive receptor, has been observed in Rab7-positive late endosomes (Arjonen et al, 2012).…”

Emerging properties of adhesion complexes: what are they and what do they do?

“…However, FN binding has been shown to induce a5b1 ubiquitination and drives ESCRT-dependent delivery of FN-a5b1 to multi-vesicular bodies for lysosomal degradation [107,108] (see Figure 2 in main text). It is not yet known whether similar mechanisms regulate degradation of all integrin heterodimers; however, potential ubiquitination sites have been identified in other a-subunits [122]. If it transpires that all integrin heterodimers are subject to ubiquitin-dependent degradation, it will be important to determine how different ubiquitin ligases and deubiquitinating enzymes are spatially and temporally co-ordinated to regulate heterodimer-specific degradation.…”