High Polymorphism Levels of De Novo ORFs in a Yoruba Human Population.

During evolution, new open reading frames (ORFs) with the potential to give rise to novel proteins continuously emerge. A recent compilation of noncanonical ORFs with translation signatures in humans has identified thousands of cases with a putative de novo origin. However, it is not known which is their distribution in the population. Are they universally translated? Here, we use ribosome profiling data from 65 lymphoblastoid cell lines from individuals of Yoruba origin to investigate this question. We identify 2,587 de novo ORFs translated in at least one of the cell lines. In line with their de novo origin, the encoded proteins tend to be smaller than 100 amino acids and encode positively charged proteins. We observe that the de novo ORFs are more polymorphic in the population than the set of canonical proteins, with a substantial fraction of them being translated in only some of the cell lines. Remarkably, this difference remains significant after controlling for differences in the translation levels. These results suggest that variations in the level translation of de novo ORFs could be a relevant source of intraspecies phenotypic diversity in humans.

Microproteins encoded by noncanonical ORFs are a major source of tumor-specific antigens in a liver cancer patient meta-cohort.

The expression of tumor-specific antigens during cancer progression can trigger an immune response against the tumor. Here, we investigate if microproteins encoded by noncanonical open reading frames (ncORFs) are a relevant source of tumor-specific antigens. We analyze RNA sequencing data from 117 hepatocellular carcinoma (HCC) tumors and matched healthy tissue together with ribosome profiling and immunopeptidomics data. Combining human leukocyte antigen-epitope binding predictions and experimental validation experiments, we conclude that around 40% of the tumor-specific antigens in HCC are likely to be derived from ncORFs, including two peptides that can trigger an immune response in humanized mice. We identify a subset of 33 tumor-specific long noncoding RNAs expressing novel cancer antigens shared by more than 10% of the HCC samples analyzed, which, when combined, cover a large proportion of the patients. The results of the study open avenues for extending the range of anticancer vaccines.