Abstract CYRI proteins promote lamellipodial dynamics by opposing Rac1-mediated activation of the Scar/WAVE complex. This activity also supports resolution of macropinocytic cups, promoting internalisation of surface proteins, including integrins. Here, we show that CYRI-B also promotes focal adhesion maturation and dynamics. Focal adhesions in CYRI-B-depleted cells show accelerated maturation and become excessively large. We probed the composition of these enlarged focal adhesions, using a Bio-ID screen, with paxillin as bait. Our screen revealed changes in the adhesome suggesting early activation of stress fibre contraction and depletion of the integrin internalisation mediator ERC1. Lack of CYRI-B leads to more stable lamellipodia and accumulation of polymerised actin in stress fibres. This actin acts as a barrier to microtubule targeting for adhesion turnover. Thus, our studies reveal an important connection between lamellipodia dynamics controlled by CYRI-B and microtubule targeting of ERC1 to modulate adhesion maturation and turnover.

CYRI-B loss promotes enlarged mature focal adhesions and restricts microtubule and ERC1 access to the cell leading edge