Moesin Serves as Scaffold Protein for PD-L1 in Human Uterine Cervical Squamous Carcinoma Cells

Abstract

Immune checkpoint blockade (ICB) therapy targeting the programmed death ligand-1 (PD-L1)/PD-1 axis has emerged as a promising treatment for uterine cervical cancer; however, only a small subset of patients with uterine cervical squamous cell carcinoma (SCC) derives clinical benefit from ICB therapies. Thus, there is an urgent unmet medical need for novel therapeutic strategies to block the PD-L1/PD-1 axis in patients with uterine cervical SCC. Here, we investigated the involvement of ezrin/radixin/moesin (ERM) family scaffold proteins, which crosslink several plasma membrane proteins with the actin cytoskeleton, on the plasma membrane localization of PD-L1 in BOKU and HCS-2 cells derived from human uterine cervical SCC. Immunofluorescence analysis showed that PD-L1 colocalized with all three ERM proteins in the plasma membrane. Gene knockdown of moesin, but not ezrin and radixin, substantially reduced the plasma membrane expression of PD-L1, with limited effect on mRNA expression. An immunoprecipitation assay demonstrated the molecular interaction between PD-L1 and moesin. Moreover, phosphorylated, i.e., activated, moesin was highly colocalized with PD-L1 in the plasma membrane. In conclusion, moesin may be a scaffold protein responsible for the plasma membrane expression of PD-L1 in human uterine cervical SCC.

New Insights into Immunotherapy for Gynecological Cancer

“…Furthermore, they also showed a higher expression of PD-L1 in the tumor samples from patients with cervical SCC and a lower survival probability in the cervical SCC patients who had high moesin expression than those who had low/medium moesin expression. This was achieved using data from The Cancer Genome Atlas, partly supporting their idea that there is a possible correlation between PD-L1 and moesin in uterine cervical SCC [ 29 ].…”

“…Similarly, Tameishi M. and Ishikawa H. et al found that ezrin also contributes to the cell surface plasma membrane localization of PD-L1 in the human epithelial ovarian cancer cell line A2780 cells [ 28 ]. Subsequently, Doukuni R. and colleagues demonstrated that in the human cervical squamous cell carcinoma (SCC) BOKU and HCS-2 cell lines, plasma membrane co-localization and protein–protein interaction of PD-L1 takes place with all three ERM proteins by means of immunofluorescence microscopy or co-immunoprecipitation experiments using a specific antibody against PD-L1, respectively [ 29 ]. Intriguingly, Doukuni R. et al discovered that RNAi-mediated knockdown of moesin—but not ezrin and radixin—significantly reduced the cell surface expression of PD-L1 with little impact on its mRNA expression, illuminating the unexpected role of moesin in the plasma membrane localization of PD-L1, possibly via post-translational modification process, as it served as a scaffold protein in the human cervical SCC [ 29 ].…”

“…Subsequently, Doukuni R. and colleagues demonstrated that in the human cervical squamous cell carcinoma (SCC) BOKU and HCS-2 cell lines, plasma membrane co-localization and protein–protein interaction of PD-L1 takes place with all three ERM proteins by means of immunofluorescence microscopy or co-immunoprecipitation experiments using a specific antibody against PD-L1, respectively [ 29 ]. Intriguingly, Doukuni R. et al discovered that RNAi-mediated knockdown of moesin—but not ezrin and radixin—significantly reduced the cell surface expression of PD-L1 with little impact on its mRNA expression, illuminating the unexpected role of moesin in the plasma membrane localization of PD-L1, possibly via post-translational modification process, as it served as a scaffold protein in the human cervical SCC [ 29 ]. Furthermore, they also showed a higher expression of PD-L1 in the tumor samples from patients with cervical SCC and a lower survival probability in the cervical SCC patients who had high moesin expression than those who had low/medium moesin expression.…”

RNA methylation-related genes of m6A, m5C, and m1A predict prognosis and immunotherapy response in cervical cancer

“…[ 23 ] found that the combination of TILs and anti-PD1 significantly improves the prognosis of metastatic cervical cancer. However, only a small proportion of patients with squamous cell carcinoma (SCC) of the uterine cervix derive clinical benefits from ICB therapy [ 24 ]. A study by Ari found that 30% of cervical malignancies are positive for cytotoxic T-lymphocyte antigen 4 (CTLA4) [ 25 ].…”

Cellular Membrane Localization of Innate Immune Checkpoint Molecule CD47 Is Regulated by Radixin in Human Pancreatic Ductal Adenocarcinoma Cells

“…The ezrin/radixin/moesin (ERM) family members are the three closely related proteins that post-translationally modulate the cellular membrane localization of numerous cancer-related transmembrane proteins by crosslinking with the actin cytoskeleton [ 19 , 20 , 21 , 22 ]. Our laboratory recently demonstrated that the ERM family post-translationally modulates the cellular surface localization of PD-L1, which belongs to a group of IgG superfamilies similar to CD47, by serving as a scaffold protein in several cancer cell types, including PDAC [ 23 , 24 , 25 , 26 , 27 ]. However, it is unclear whether the ERM family is involved in the cellular membrane localization of CD47 through post-translational modifications in cancer cells.…”