Phosphorylated RB Promotes Cancer Immunity by Inhibiting NF-κB Activation and PD-L1 Expression

Area of Science:

• Oncology
• Molecular Biology
• Immunology

Background:

• Aberrant programmed death ligand-1 (PD-L1) expression in tumors hinders anti-cancer immunity.
• Retinoblastoma protein (RB) is a crucial tumor suppressor regulating cell cycle and DNA damage.
• The interaction between RB and nuclear factor κB (NF-κB) in immune regulation is not fully understood.

Purpose of the Study:

• To elucidate the role of RB in regulating PD-L1 expression via the NF-κB pathway.
• To investigate the impact of RB phosphorylation on NF-κB activity and PD-L1 levels.
• To explore the therapeutic potential of targeting the RB-NF-κB axis for cancer immunotherapy.

Main Methods:

• Co-immunoprecipitation to assess RB-NF-κB p65 interaction.
• RNA sequencing (RNA-seq) to analyze gene expression changes upon RB knockdown or CDK4/6 inhibition.
• Analysis of patient samples to correlate RB phosphorylation with PD-L1 expression.
• In vivo studies using RB-derived peptides to evaluate therapeutic efficacy.

Main Results:

• RB directly interacts with NF-κB p65, dependent on CDK4/6-mediated phosphorylation at S249/T252.
• RB knockdown or CDK4/6 inhibition upregulates PD-L1 and other NF-κB target genes.
• S249/T252-phosphorylated RB inversely correlates with PD-L1 expression in patient tumors.
• A phosphorylation-mimetic RB peptide suppressed radiotherapy-induced PD-L1 upregulation and improved treatment efficacy in vivo.

Conclusions:

• Hyperphosphorylated RB functions as a tumor suppressor by inhibiting NF-κB and PD-L1 expression.
• The RB-NF-κB pathway represents a novel target for overcoming cancer immune evasion.
• Targeting this axis may enhance the efficacy of conventional and targeted cancer therapies.