Ribosomal Proteins Regulate MHC Class I Peptide Generation for Immunosurveillance

The MHC class I antigen presentation system enables T cell immunosurveillance of cancers and viruses. Rapidly degraded nascent polypeptides (DRiPs) provide many class I peptide ligands. By knocking down each of the 80 ribosomal proteins, we identified proteins that modulate peptide generation without altering source protein expression. We show that 60S ribosomal proteins L6 (RPL6) and RPL28, which are adjacent on the ribosome, play opposite roles in generating an influenza A virus encoded peptide. RPL6 depletion decreases ubiquitin-dependent peptide presentation, while RPL28 depletion increases ubiquitin-dependent and -independent peptide presentation. 40S ribosomal protein S28 (RPS28) knockdown increases total peptide supply in uninfected cells by increasing DRiP synthesis from non-canonical translation of “untranslated” regions and non-AUG start codons, and sensitizes tumor cells for T cell targeting. RPL23 knocKDut decreases overall peptide supply, impairing T cell recognition of tumor cells. Our findings raise the possibility of modulating immunosurveillance by pharmacologically targeting ribosomes. HEK293-Kb cells transduced with lentiviruses to knockdown RPS28, RPLP0, RPL3, RPL6, RPL28 protein, or scrambled control.