Podoplanin binds ERM proteins to activate RhoA and promote epithelial-mesenchymal transition

TLDR

Podoplanin is a small membrane mucin expressed in tumors associated with malignant progression and is enriched at cell‑surface protrusions where it colocalizes with ERM proteins. Using mutant podoplanin‑GFP constructs, the authors show that interaction of the cytoplasmic tail with ERM proteins is required to upregulate RhoA activity and drive epithelial‑mesenchymal transition. Podoplanin directly binds ezrin/moesin via a basic cytoplasmic tail dipeptide, induces EMT in MDCK cells through RhoA activation, enhances migration and invasiveness, and its effects are blocked by dominant‑negative ezrin or RhoA mutants, underscoring its role in cell motility.

Abstract

Podoplanin is a small membrane mucin expressed in tumors associated with malignant progression. It is enriched at cell-surface protrusions where it colocalizes with members of the ERM (ezrin, radixin, moesin) protein family. Here, we found that human podoplanin directly interacts with ezrin (and moesin) in vitro and in vivo through a cluster of basic amino acids within its cytoplasmic tail, mainly through a juxtamembrane dipeptide RK. Podoplanin induced an epithelial-mesenchymal transition in MDCK cells linked to the activation of RhoA and increased cell migration and invasiveness. Fluorescence time-lapse video observations in migrating cells indicate that podoplanin might be involved in ruffling activity as well as in retractive processes. By using mutant podoplanin constructs fused to green fluorescent protein we show that association of the cytoplasmic tail with ERM proteins is required for upregulation of RhoA activity and epithelial-mesenchymal transition. Furthermore, expression of either a dominant-negative truncated variant of ezrin or a dominant-negative mutant form of RhoA blocked podoplanin-induced RhoA activation and epithelial-mesenchymal transition. These results provide a mechanistic basis to understand the role of podoplanin in cell migration or invasiveness.