Novel function for AP-1B during cell migration

Abstract

The epithelial cell-specific clathrin adaptor AP-1B has a well-established role in polarized sorting of cargos to the basolateral membrane. Here we show that β1 integrin was dependent on AP-1B and its co-adaptor, autosomal recessive hypercholesterolemia protein (ARH), for sorting to the basolateral membrane. We further demonstrate an unprecedented role for AP-1B at the basal plasma membrane during collective cell migration of epithelial sheets. During wound healing, expression of AP-1B (and ARH in AP-1B-positive cells) slowed epithelial-cell migration. We show that AP-1B colocalized with β1 integrin in focal adhesions during cell migration using confocal microscopy and total internal reflection fluorescence (TIRF) microscopy on fixed specimens. Further, AP-1B labeling in cell protrusion was distinct from labeling for the endocytic adaptor complex AP-2. Using stochastic optical reconstruction microscopy (STORM) we identified numerous AP-1B-coated structures at or close to the basal plasma membrane in cell protrusions. In addition, immuno-electron microscopy (EM) showed AP-1B in coated pits and vesicles at the plasma membrane during cell migration. Lastly, qRT-PCR analysis of human epithelial-derived cell lines revealed a loss of AP-1B expression in highly migratory metastatic cancer cells suggesting that AP-1B's novel role at the basal plasma membrane during cell migration might be an anti-cancer mechanism. [Media: see text] [Media: see text]

Multifaceted control of E-cadherin dynamics by the Adaptor Protein Complex 1 during epithelial morphogenesis

“…We demonstrate that this AP-1 function is accompanied by transcriptional feedback which maintains E-cad levels at the cell surface. In line with the correlation of the AP-1B loss with the metastatic potential in humans [66], our findings highlight the pivotal role of the AP-1 complex in preventing tumour progression and enabling correct epithelial morphogenesis.…”

“…Intriguingly, E-cad endocytosis was enhanced upon the loss of AP-1, as it is a trafficking adaptor usually thought to promote vesicular transport. Similarly, in mammalian cells (LLC-PK1), expression of AP-1B slowed down cell migration which is consistent with the reduced integrin turnover [66,74]. One of the scenarios proposed for the AP-1B function at the plasma membrane in these cells was that AP-1B forms coats that abort without scission but at the same time occupy binding sites for AP-2 and thus reduce the net rate of AP-2mediated endocytosis.…”

“…While localization of AP-1 at AJs was not previously reported, it is not surprising as AP-1 has been found at the plasma membrane in such diverse systems as the cell-ECM adhesion in mammalian kidney cells and phagosomes in Dictyostelium amoebae [66,67].…”

“…Although the mammalian μ subunits are 79% identical, AP-1A sorts basolateral cargos at the TGN, where it is recruited by the small GTPase Arf1 [27,[29][30][31] and AP-1B sorts proteins from REs to the basolateral membrane and is regulated by the small GTPase Arf6 (Shteyn et al, 2011). AP-1B is also found at integrin-mediated focal adhesions, and its loss correlates with the migratory behaviour of metastatic cells (Kell et al, 2020).…”

Role of adaptin protein complexes in intracellular trafficking and their impact on diseases

“…In addition, upregulation of AP1M1 is putatively a biomarker for metastasis to the brain tissue [ 46 ]. On the other hand, AP1M2 containing AP1 complex was recently proposed to control β1 integrin transport in the basal membrane of epithelial cells and act as a cell-inherent anticancer mechanism that can inhibit metastasis [ 47 ]. There are three AP1 σ subunits: AP1S1, AP1S2, and AP1S3.…”