The LINC01315-encoded small protein YAPer-ORF competes with PRP4k to hijack YAP signaling to aberrantly promote cell growth.

The dysregulation of YAP activity is implicated in abnormal organ size and the pathogenesis of diverse diseases, including cancer. However, the functional regulation of YAP activity by lncRNA-encoded peptides remains elusive. In this study, we report the identification of a small protein (93 aa) encoded by the lncRNA LINC01315. This small protein, termed YAPer-ORF, preferentially interacted with GNAQ/11 mutants to augment YAP activity. Mechanistically, YAPer-ORF was located in the nucleus and competed with YAP to bind the nuclear kinase PRP4K to hinder YAP phosphorylation. This decreased phosphorylation of YAP by YAPer-ORF promoted YAP retention in the nucleus and facilitated the expression of downstream target genes such as CCND1. In both cancerous and noncancerous models, YAPer-ORF prominently drove cell proliferation in a CCND1-dependent manner. Notably, cardiac-specific genetic knock-in of the human YAPer-ORF in mice significantly increased heart size through increased cardiomyocyte proliferation, underscoring the role of YAPer-ORF in cell proliferation. Moreover, treatment with an anti-YAPer-ORF neutralizing antibody effectively suppressed uveal melanoma growth, highlighting the therapeutic potential of targeting YAPer-ORF. These findings collectively establish YAPer-ORF as a critical regulator of YAP activity, further highlighting the disruption of YAPer-ORF activity as a potential therapeutic strategy against YAP-driven human cancers and developmental diseases.