Cyclin D-CDK4 kinase destabilizes PD-L1 via cullin 3-SPOP to control cancer immune surveillance

Nature. 2018 Jan 4;553(7686):91-95. doi: 10.1038/nature25015. Epub 2017 Nov 16.


Treatments that target immune checkpoints, such as the one mediated by programmed cell death protein 1 (PD-1) and its ligand PD-L1, have been approved for treating human cancers with durable clinical benefit. However, many patients with cancer fail to respond to compounds that target the PD-1 and PD-L1 interaction, and the underlying mechanism(s) is not well understood. Recent studies revealed that response to PD-1-PD-L1 blockade might correlate with PD-L1 expression levels in tumour cells. Hence, it is important to understand the mechanistic pathways that control PD-L1 protein expression and stability, which can offer a molecular basis to improve the clinical response rate and efficacy of PD-1-PD-L1 blockade in patients with cancer. Here we show that PD-L1 protein abundance is regulated by cyclin D-CDK4 and the cullin 3-SPOP E3 ligase via proteasome-mediated degradation. Inhibition of CDK4 and CDK6 (hereafter CDK4/6) in vivo increases PD-L1 protein levels by impeding cyclin D-CDK4-mediated phosphorylation of speckle-type POZ protein (SPOP) and thereby promoting SPOP degradation by the anaphase-promoting complex activator FZR1. Loss-of-function mutations in SPOP compromise ubiquitination-mediated PD-L1 degradation, leading to increased PD-L1 levels and reduced numbers of tumour-infiltrating lymphocytes in mouse tumours and in primary human prostate cancer specimens. Notably, combining CDK4/6 inhibitor treatment with anti-PD-1 immunotherapy enhances tumour regression and markedly improves overall survival rates in mouse tumour models. Our study uncovers a novel molecular mechanism for regulating PD-L1 protein stability by a cell cycle kinase and reveals the potential for using combination treatment with CDK4/6 inhibitors and PD-1-PD-L1 immune checkpoint blockade to enhance therapeutic efficacy for human cancers.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • 14-3-3 Proteins / metabolism
  • Animals
  • B7-H1 Antigen / biosynthesis
  • B7-H1 Antigen / metabolism*
  • Cdh1 Proteins / metabolism
  • Cell Cycle
  • Cell Line
  • Cullin Proteins / metabolism*
  • Cyclin D / metabolism*
  • Cyclin-Dependent Kinase 4 / antagonists & inhibitors
  • Cyclin-Dependent Kinase 4 / metabolism*
  • Cyclin-Dependent Kinase 6 / antagonists & inhibitors
  • Female
  • Humans
  • Immunologic Surveillance*
  • Lymphocytes, Tumor-Infiltrating / cytology
  • Lymphocytes, Tumor-Infiltrating / immunology
  • Male
  • Mice
  • Neoplasms / immunology*
  • Nuclear Proteins / chemistry
  • Nuclear Proteins / metabolism*
  • Phosphorylation
  • Programmed Cell Death 1 Receptor / metabolism
  • Prostatic Neoplasms / immunology
  • Proteasome Endopeptidase Complex / metabolism
  • Protein Stability
  • Proteolysis
  • Repressor Proteins / chemistry
  • Repressor Proteins / metabolism*
  • Tumor Escape / immunology*


  • 14-3-3 Proteins
  • B7-H1 Antigen
  • CD274 protein, human
  • Cdh1 Proteins
  • Cullin Proteins
  • Cyclin D
  • FZR1 protein, human
  • Nuclear Proteins
  • PDCD1 protein, human
  • Programmed Cell Death 1 Receptor
  • Repressor Proteins
  • SPOP protein, human
  • CDK4 protein, human
  • CDK6 protein, human
  • Cyclin-Dependent Kinase 4
  • Cyclin-Dependent Kinase 6
  • Proteasome Endopeptidase Complex