Widespread pre-translational regulation of the inclusion of signal peptides in human proteins.

Signal peptides (SP) are cleavable N-terminal protein motifs used co-translationally for entry of nascent polypeptides into the secretory pathway. Their co-translational cleavage prevents their extensive post-translational regulation and flexibility in their usage is made possible by the control of their inclusion at a pre-translational level. To characterize this regulation on a transcriptome scale, we analyzed the level and mechanisms of inclusion of the 3298 most likely human SP-encoding genes, 47% of which alternatively express their SP. Analysis of RNA-seq data across different normal human tissues indicates that pre-translational regulation of the SP differs depending on tissue-coverage of the gene, with alternative SP genes more likely to be widely expressed than constitutive SP genes. SP inclusion represents a new metric to measure functional gene expression and its deregulation in disease. Our analysis supports the extensive use of pre-translational regulation of SP inclusion, with functional consequences and implications for biomarker discovery.