ERM proteins colocalize with the Na+/H+ exchanger NHE1 in MCF‐7 breast cancer cell invadopodia and affect invadopodia number

Abstract

Invadopodia are actin‐rich membrane protrusions which have been assigned essential roles in cancer cell invasiveness. Here, we investigate the roles of ezrin, radixin and moesin (ERM), three closely related F‐actin‐plasma membrane linker proteins implicated in metastasis, and their binding partner the Na+/H+ exchanger isoform 1 (NHE1), in the formation and function of invadopodial rosettes in MCF‐7 human breast cancer cells. ERM proteins colocalized strongly with NHE1 in invadopodia in MCF‐7 cells +/− constitutively active, N‐terminally truncated ErbB2 (ΔNErbB2). In contrast, the tumor suppressor Merlin which is more distantly related to the ERM proteins, did not. siRNA‐mediated knockdown of NHE1 increased the average number of invadopodia per cell in ΔNErbB2‐expressing cells but not in vector controls. Overexpression of either dominant negative (DN) or constitutively active (CA) ezrin decreased the number of invadopodia per cell, in vector control cells only. Average invadopodial rosette diameter was unaffected by knockdown of ezrin or NHE1, or by expression of DN‐ or CA‐ezrin. Thus, in MCF‐7 cells, NHE1 colocalizes strongly with ERM proteins in invadopodial rosettes and both NHE1 and ezrin appear to affect their formation. Studies are ongoing to determine the generality and roles of these interactions in cancer invasiveness.Funding: Danish Cancer Society, Danish Research Council