Membranous and Cytoplasmic Expression of PD-L1 in Ovarian Cancer Cells

Abstract

Background: Expression of programmed death-ligand 1 (PD-L1) on tumor cells represents a powerful immune evasion pathway, but the role of intracellular or cytoplasmic PD-L1 has not been investigated in ovarian cancer cells. Methods: Flow cytometry (FCM), Real-time PCR (qPCR), immunohistochemistry (IHC) and western blot were used to determine the expression of PD-L1 in ovarian cancer cells. The cytokines detected in the tumor or tumor associated macrophage (TAM) were used to treat cancer cells. PD-L1 blockade and silencing were used to elucidate the functional significance of cancer-related PD-L1 expression. Results: Based on the results presented, PD-L1 was found variably expressed in the cytoplasm and the cell surface of both HO8910 and SKOV3 cells. TAM or IFN-γ, TNF-α, IL-10 and IL-6 released from TAM stimulated the expression of PD-L1 at the surface of the cancer cells. The IHC results were consistent with the data in vitro showing infiltration of TAM correlated with membranous PD-L1. The increases of PD-L1 at the surface were not due to a shift in the proportion of surface versus intracellular protein, but the contribution of extracellular signal-regulated kinase (ERK)1/2 and phosphoinositide 3-kinase (PI3K) pathway activation. As a consequence, inducible membranous PD-L1 expression on SKOV3 inhibited CD8⁺ T cell function, and cytoplasmic PD-L1 promoted cancer cell growth. Additionally, in mouse models, both PD-L1 and PD-1 mAb resulted in tumor growth inhibition and demonstrated a potential to decrease the number of PD-1⁺CD8⁺T cells. Conclusion: We conclude that TAM induced PD-L1 on the cancer cells represents an immune evasion mechanism. The observations confirm the therapeutic potential of PD-L1/PD-1 mAb to reactivate anti-tumor immunity in ovarian cancer.

Adipose PD-L1 Modulates PD-1/PD-L1 Checkpoint Blockade Immunotherapy Efficacy in Breast Cancer

“…Yet a third possibility relates to the recently reported function of cytoplasmic PD-L1 in tumor progression. 56 While adipocyte PD-L1 is prominently present on the cell surface, we also observe a sub-population of internally localized endogenous PD-L1 in adipocytes and ectopic PD-L1 in our inducible 3T3L1 cell system. This internal pool of PD-L1 could influence antitumor immunity via a signaling pathway independent of the conventional mechanism involving cell surface PD-L1/PD-1.…”

Persistent restoration to the immunosupportive tumor microenvironment in glioblastoma by bevacizumab

“…This phenomenon could be attributable to the inhibition of VEGF‐dependent upregulation of PD‐L1. In addition, inhibition of immunosuppressive cells, including TAMs, under or after Bev might also have contributed to the decrease of the percentage of tumor cells expressing PD‐L1, because soluble inflammatory factors such as γ‐interferon, tumor necrosis factor‐α, IL‐10 and IL‐6 derived from TAMs were known to induce PD‐L1 of cancer cells …”

Cisplatin‐induced programmed cell death ligand‐2 expression is associated with metastasis ability in oral squamous cell carcinoma

“…In bladder cancer, cisplatin treatment serves to upregulate PD‐L1 expression via the ERK signaling pathway, followed by AP‐1. In addition, PD‐L1 is variably expressed in the cytoplasm and cell membrane in ovarian cancer cells . However, the mechanism of cisplatin‐induced PD‐L1 expression in these tumor cells remains largely unclear.…”