The Cell-Autonomous Pro-Metastatic Activities of PD-L1 in Breast Cancer Are Regulated by N-Linked Glycosylation-Dependent Activation of STAT3 and STAT1

• Published in: Cells (Basel, Switzerland) Switzerland), 2023-09, Vol.12 (19), p.2338
• Main Authors: Erlichman, Nofar, Meshel, Tsipi, Baram, Tamir, Abu Raiya, Alaa, Horvitz, Tamar, Ben-Yaakov, Hagar, Ben-Baruch, Adit
• Format: Article
• Language: English
• Subjects: Antibodies; Breast cancer; Cancer therapies; Cell growth; Cell proliferation; Chemokines; Complications and side effects; Development and progression; Flow cytometry; Glycosylation; Health aspects; Immune checkpoint inhibitors; Laboratories; Lymphocytes; Lymphocytes T; Mannosidase; Medical research; Medicine, Experimental; Metastases; Metastasis; N-linked glycosylation; PD-1; PD-L1; PD-L1 protein; Proteins; R&D; Research & development; Response rates; Risk assessment; siRNA; STAT1; Stat1 protein; STAT3; Stat3 protein; Tumors
• ISSN: 2073-4409; 2073-4409
• DOI: 10.3390/cells12192338

PD-L1 has been characterized as an inhibitory immune checkpoint, leading to the suppression of potential anti-tumor immune activities in many cancer types. In view of the relatively limited efficacy of immune checkpoint blockades against PD-L1 in breast cancer, our recent study addressed the possibility that in addition to its immune-inhibitory functions, PD-L1 promotes the pro-metastatic potential of the cancer cells themselves. Indeed, our published findings demonstrated that PD-L1 promoted pro-metastatic functions of breast cancer cells in a cell-autonomous manner, both in vitro and in vivo. These functions fully depended on the integrity of the S283 intracellular residue of PD-L1. Here, using siRNAs and the S283A-PD-L1 variant, we demonstrate that the cell-autonomous pro-metastatic functions of PD-L1—tumor cell proliferation and invasion, and release of the pro-metastatic chemokine CXCL8—required the activation of STAT3 and STAT1 in luminal A and triple-negative breast cancer cells. The cell-autonomous pro-metastatic functions of PD-L1 were potently impaired upon inhibition of N-linked glycosylation (kifunensine). Site-specific mutants at each of the N-linked glycosylation sites of PD-L1 (N35, N192, N200, and N219) revealed that they were all required for PD-L1-induced pro-metastatic functions to occur; the N219 site was the main regulator of STAT3 and STAT1 activation, with accompanying roles for N192 and N200 (depending on the cell type). Using a T cell-independent mouse system, we found that cells expressing N35A-PD-L1 and N219A-PD-L1 had a significantly lower tumorigenic and metastatic potential than cells expressing WT-PD-L1. TCGA analyses revealed significant associations between reduced survival and high levels of α-mannosidase II (inferring on N-linked glycosylation) in breast cancer patients. These findings suggest that N-linked glycosylation of PD-L1 may be used to screen for patients who are at greater risk of disease progression, and that modalities targeting N-linked glycosylated PD-L1 may lead to the inhibition of its cell-autonomous pro-metastatic functions and to lower tumor progression in breast cancer.