Inducible but Not Constitutive Expression of PD-L1 in Human Melanoma Cells Is Dependent on Activation of NF-κB

Abstract

Monoclonal antibodies against immune checkpoint blockade have proven to be a major success in the treatment of melanoma. The programmed death receptor-1 ligand-1 (PD-L1) expression on melanoma cells is believed to have an inhibitory effect on T cell responses and to be an important escape mechanism from immune attack. Previous studies have shown that PD-L1 can be expressed constitutively or can be induced by IFN-γ secreted by infiltrating lymphocytes. In the present study we have investigated the mechanism underlying these two modes of PD-L1 expression in melanoma cells including cells that had acquired resistance to the BRAF inhibitor vemurafenib. PD-L1 expression was examined by flow cytometry and immunoblotting. Specific inhibitors and siRNA knockdown approaches were used to examine the roles of the RAF/ MEK, PI3K, NF-κB, STAT3 and AP1/ c-Jun pathways. IFN-γ inducible expression of PD-L1 was dependent on NF-κB as shown by inhibition with BMS-345541, an inhibitor of IκB and the BET protein inhibitor I-BET151, as well as by siRNA knockdown of NF-κB subunits. We were unable to implicate the BRAF/MEK pathway as major regulators in PD-L1 expression on vemurafenib resistant cells. Similarly the PI3K/AKT pathway and the transcription factors STAT3 and c-Jun had only minor roles in IFN-γ induced expression of PD-L1. The mechanism underlying constitutive expression remains unresolved. We suggest these results have significance in selection of treatments that can be used in combination with monoclonal antibodies against PD1, to enhance their effectiveness and to reduce inhibitory effects melanoma cells have against cytotoxic T cell activity.

Programmed Death Ligand-1 (PD-L1) Expression in the Programmed Death Receptor-1 (PD-1)/PD-L1 Blockade: A Key Player Against Various Cancers

“…14 Furthermore, interferons, especially interferon c, are the most common inducer in adaptive immunemediated PD-L1 upregulation on tumor cells or on tumorinfiltrated leukocytes, including melanoma 15 and ovarian cancer. 2,16 Other inflammatory signaling pathways, including interleukin 4, interleukin 10, vascular endothelial growth factor, granulocyte colony-stimulating factor, and bacterial lipopolysaccharide, have also been shown to induce the expression of PD-L1.…”

“…Using a similar approach with different antibodies, a study showed a higher expression of PD-1/PD-L1 in CD4/CD8 T lymphocytes from chronic lymphocytic leukemia patients when compared with age-matched controls. 49 In addition to peripheral blood cells or lymphocytes, Gowrishankar et al 15 have shown that interferon c induces the upregulation of PD-L1 in a nuclear factor-jB-dependent fashion in 5 different melanoma cell lines and melanoma patient-derived cells using flow cytometry. 15 Furthermore, Andorsky et al 50 documented that PD-L1 is widely expressed by anaplastic large cell lymphoma, whereas it only has limited expression in diffuse large B-cell lymphoma (DLBCL).…”

Deubiquitination and Stabilization of PD-L1 by CSN5

“…Because programmed death-1 (PD-1) and PD-L1 blockade have yielded promising clinical effects, understanding the regulatory mechanism of PD-L1 may identify biomarkers and/or develop combinatorial strategies for clinical use (Pardoll, 2012). While transcriptional regulation of PD-L1 via STAT, NF-κB, or NFAT has been reported (Gowrishankar et al, 2015; Huang et al, 2013; Peng et al, 2015), it remains unclear whether and how PD-L1 is posttranscriptionally regulated.…”

Pharmacometrics and systems pharmacology of immune checkpoint inhibitor nivolumab in cancer translational medicine

“…(b) tumor heterogeneity: there are wide intra-and inter-tumoral variations in the expression of PD-L1, indicating that sampling of tumor tissues may also impinge on the outcome of PD-L1 detection [26] ; (c) low specificity: tumors that do not express detectable levels of PD-L1 on the cell surface can also respond to antibodies against PD-1, suggesting that the predictive value of PD-L1 expression may not be uniformly applicable to all types of cancer [26] ; (d) inducible gene expression: PD-L1 can be expressed constitutively or can be induced by IFN- [28,29] secreted by infiltrating lymphocytes or by IL-27 [30] ; and (e ) potential drug resistance: resistance to PD-L1 inhibitors may be a cause of therapeutic failure, however, this has not been well-studied at the current time and needs systematic investigation [26] . PD-L1 has been reported to be modulated by MAPK and PI3K/AkT/mTOR oncogenic signaling pathways [31,32] .…”