Trans-Regulation of Alternative PD-L1 mRNA Processing by CDK12 in Non-Small-Cell Lung Cancer Cells

Area of Science:

• Oncology
• Molecular Biology
• Immunology

Background:

• Immunotherapy targeting PD-1/PD-L1 interactions shows promise in non-small-cell lung cancer (NSCLC).
• Patient response to PD-1/PD-L1 blockade varies, potentially due to PD-L1 expression heterogeneity.
• Alternative splicing of PD-L1 mRNA generates soluble (sPD-L1) and membrane-bound (mPD-L1) forms, influencing therapeutic efficacy.

Purpose of the Study:

• To identify factors regulating the ratio of PD-L1 mRNA variants in NSCLC cells.
• To investigate the role of CDK12 in PD-L1 alternative polyadenylation.
• To explore the impact of CDK12 modulation on sPD-L1/mPD-L1 balance.

Main Methods:

• Verification of alternative PD-L1 RNA processing in NSCLC cell lines.
• In silico analysis to identify potential regulatory factors.
• CRISPR/Cas9-mediated loss-of-function mutations in CDK12.
• Treatment with CDK12/13 inhibitor THZ531.
• Quantitative analysis of PD-L1 mRNA variants and protein isoforms.

Main Results:

• Alternative PD-L1 RNA processing generating PD-L1v4 (sPD-L1) and PD-L1v1 (mPD-L1) was confirmed in NSCLC cells.
• Loss-of-function mutations in CDK12 significantly increased the PD-L1v4/PD-L1v1 mRNA ratio.
• CDK12 inhibition with THZ531 also elevated the PD-L1v4/PD-L1v1 ratio and modulated PD-L1 response to IFN-γ.
• CDK12 promotes transcriptional elongation, suppressing alternative polyadenylation within introns.

Conclusions:

• CDK12 plays a critical role in regulating the balance between soluble and membrane-bound PD-L1 isoforms in NSCLC.
• Modulation of CDK12 activity influences PD-L1 transcript variant formation.
• Findings suggest CDK12 as a potential target for optimizing PD-1/PD-L1 blockade immunotherapy in NSCLC.