PD-L1 up-regulation in melanoma increases disease aggressiveness and is mediated through miR-17-5p

Valentina Audrito, Sara Serra, Aureliano Stingi, Francesca Orso, Federica Gaudino, Cinzia Bologna, Francesco Neri, Giulia Garaffo, Romina Nassini, Gianna Baroni, Eliana Rulli, Daniela Massi, Salvatore Oliviero, Roberto Piva, Daniela Taverna, Mario Mandalà, Silvia Deaglio

Research output: Contribution to journalArticlepeer-review

Abstract

PD-L1 is expressed by a subset of patients with metastatic melanoma (MM) with an unfavorable outcome. Its expression is increased in cells resistant to BRAF or MEK inhibitors (BRAFi or MEKi). However, the function and regulation of expression of PDL1 remain incompletely understood. After generating BRAFi- and MEKi-resistant cell lines, we observed marked upregulation of PD-L1 expression. These cells were characterized by a common gene expression profile with up-regulation of genes involved in cell movement. Consistently, in vitro they showed significantly increased invasive properties. This phenotype was controlled in part by PD-L1, as determined after silencing the molecule. Up-regulation of PD-L1 was due to post-transcriptional events controlled by miR-17-5p, which showed an inverse correlation with PD-L1 mRNA. Direct binding between miR-17-5p and the 3'-UTR of PD-L1 mRNA was demonstrated using luciferase reporter assays. In a cohort of 80 BRAF-mutated MM patients treated with BRAFi or MEKi, constitutive expression of PD-L1 in the absence of immune infiltrate, defined the patient subset with the worst prognosis. Furthermore, PD-L1 expression increased in tissue biopsies after the metastatic lesions became resistant to BRAFi or MEKi. Lastly, plasmatic miR-17-5p levels were higher in patients with PD-L1+ than PD-L1- lesions. In conclusion, our findings indicate that PD-L1 expression induces a more aggressive behavior in melanoma cells. We also show that PD-L1 up-regulation in BRAFi or MEKi-resistant cells is partly due to post-transcriptional mechanisms that involve miR-17-5p, suggesting that miR-17-5p may be used as a marker of PD-L1 expression by metastatic lesions and ultimately a predictor of responses to BRAFi or MEKi.

Original languageEnglish
Pages (from-to)15894-15911
Number of pages18
JournalOncotarget
Volume8
Issue number9
DOIs
Publication statusPublished - Jan 1 2017

Keywords

  • Melanoma
  • MicroRNA
  • Regulation of gene expression
  • Resistance to therapy
  • Targeted therapy

ASJC Scopus subject areas

  • Oncology

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