This study investigates the role of antisense RNA in epigenetic silencing of tumor suppressor genes (TSGs), focusing on the cyclin-dependent kinase inhibitor p15. The authors found that p15 antisense (p15AS) RNA is highly expressed in leukemia cells and negatively correlates with p15 sense expression. They engineered constructs to test the effect of p15AS on p15 promoter activity, showing that p15AS induces silencing of p15 both in cis and trans through heterochromatin formation, rather than DNA methylation. The silencing effect persisted even after p15AS expression was turned off, and it was independent of Dicer. In mouse embryonic stem cells, p15AS expression led to p15 silencing and increased growth, with hypermethylation at the p15 promoter region observed after differentiation. These findings suggest that antisense RNA can trigger long-lasting heritable effects on gene expression through heterochromatin formation, providing a potential molecular marker for cancer risk assessment and therapeutic target.This study investigates the role of antisense RNA in epigenetic silencing of tumor suppressor genes (TSGs), focusing on the cyclin-dependent kinase inhibitor p15. The authors found that p15 antisense (p15AS) RNA is highly expressed in leukemia cells and negatively correlates with p15 sense expression. They engineered constructs to test the effect of p15AS on p15 promoter activity, showing that p15AS induces silencing of p15 both in cis and trans through heterochromatin formation, rather than DNA methylation. The silencing effect persisted even after p15AS expression was turned off, and it was independent of Dicer. In mouse embryonic stem cells, p15AS expression led to p15 silencing and increased growth, with hypermethylation at the p15 promoter region observed after differentiation. These findings suggest that antisense RNA can trigger long-lasting heritable effects on gene expression through heterochromatin formation, providing a potential molecular marker for cancer risk assessment and therapeutic target.