Acts as a backup for CMTM6 to regulate plasma membrane expression of PD-L1/CD274, an immune inhibitory ligand critical for immune tolerance to self and antitumor immunity. May protect PD- L1/CD274 from being polyubiquitinated and targeted for degradation. . This is the function of ENSG00000183723 (CMTM4, CKLF like MARVEL transmembrane domain containing 4).