Regulation of PD-L1 through direct binding of cholesterol to CRAC motifs.

Cholesterol, an essential molecule for cell structure, function, and viability, plays crucial roles in the development, progression, and survival of cancer cells. Earlier studies have shown that cholesterol-lowering drugs can inhibit the high expression of programmed-death ligand 1 (PD-L1) that contributes to immunoevasion in cancer cells. However, the regulatory mechanism of cell surface PD-L1 abundance by cholesterol is still controversial. Here, using nuclear magnetic resonance and biochemical techniques, we demonstrated that cholesterol can directly bind to the transmembrane domain of PD-L1 through two cholesterol-recognition amino acid consensus (CRAC) motifs, forming a sandwich-like architecture and stabilizing PD-L1 to prevent downstream degradation. Mutations at key binding residues prohibit PD-L1-cholesterol interactions, decreasing the cellular abundance of PD-L1. Our results reveal a unique regulatory mechanism that controls the stability of PD-L1 in cancer cells, providing an alternative method to overcome PD-L1-mediated immunoevasion in cancers.

PD-L1 degradation is regulated by electrostatic membrane association of its cytoplasmic domain.

The cytoplasmic domain of PD-L1 (PD-L1-CD) regulates PD-L1 degradation and stability through various mechanism, making it an attractive target for blocking PD-L1-related cancer signaling. Here, by using NMR and biochemical techniques we find that the membrane association of PD-L1-CD is mediated by electrostatic interactions between acidic phospholipids and basic residues in the N-terminal region. The absence of the acidic phospholipids and replacement of the basic residues with acidic residues abolish the membrane association. Moreover, the basic-to-acidic mutations also decrease the cellular abundance of PD-L1, implicating that the electrostatic interaction with the plasma membrane mediates the cellular levels of PD-L1. Interestingly, distinct from its reported function as an activator of AMPK in tumor cells, the type 2 diabetes drug metformin enhances the membrane dissociation of PD-L1-CD by disrupting the electrostatic interaction, thereby decreasing the cellular abundance of PD-L1. Collectively, our study reveals an unusual regulatory mechanism that controls the PD-L1 level in tumor cells, suggesting an alternative strategy to improve the efficacy of PD-L1-related immunotherapies.

Association study between FSHR Ala307Thr and Ser680Asn variants and polycystic ovary syndrome (PCOS) in Northern Chinese Han women.

BACKGROUND: Polycystic ovary syndrome (PCOS) is a common complex genetic endocrinopathy. It has high heritability, and twin studies indicate that it is a complex polygenic disorder. Searching for major genes of PCOS is crucial to clarify its molecular pathogenesis. A previous genome-wide association study in Chinese women with PCOS identified a region on chromosome 2p16.3 that encodes the follicle-stimulating hormone receptor (FSHR) genes as a reproducible PCOS susceptibility locus. In the present study, we performed a replication analysis of the association between two common variants of the FSHR gene and PCOS in Northern Chinese Han women. RESULTS: We recruited 384 unrelated PCOS patients and 768 healthy individuals from the Shaanxi province in the northern part of China. Two polymorphisms (Ala307Thr and Ser680Asn) of the FSHR gene and the clinical characteristics of the study subjects were analyzed in the case-control sample. The frequency of FSHR Ala307Thr and Ser680Asn variants along with the haplotype was not significantly different between the PCOS patients and the controls; however, the Ser680 variants may be associated with high levels of FSH and low E2 levels. CONCLUSION: The variant of Ser680 was not associated with PCOS but it may be related to high FSH levels. The present study suggests that the two variants of the FSHR gene are not a causative factor of PCOS in Northern Chinese Han women.