Radixin modulates the plasma membrane localization of CD47 in human uterine cervical adenocarcinoma cells

Despite the dramatic success of immune checkpoint blockers in treating numerous cancer cell types, current therapeutic modalities provide clinical benefits to a subset of patients with cervical cancers. CD47 is commonly overexpressed in a broad variety of cancer cells, correlates with poor clinical prognosis, and acts as a dominant macrophage checkpoint by interacting with receptors expressed on macrophages. It allows cancer cells to escape from the innate immune system and hence is a potential therapeutic target for developing novel macrophage checkpoint blockade immunotherapies. As the intracellular scaffold proteins, ezrin/radixin/moesin (ERM) family proteins post-translationally regulate the cellular membrane localization of numerous transmembrane proteins, by crosslinking them with the actin cytoskeleton. We demonstrated that radixin modulates the plasma membrane localization and functionality of CD47 in HeLa cells. Immunofluorescence analysis and co-immunoprecipitation assay using anti-CD47 antibody showed the colocalization of CD47 and all three ERM families in the plasma membrane, and the molecular interactions between CD47 and all three ERM. Interestingly, gene silencing of only radixin, reduced the CD47 plasma membrane localization and functionality by means of flow cytometry and phagocytosis assay but had little influence on its mRNA expression. Together, in HeLa cells radixin may function as a principal scaffold protein responsible for the CD47 plasma membrane localization.