The induction of H3K9 methylation by PIWIL4 at the p16Ink4a locus.

The field of epigenetics has made progress by the identification of the small RNA-mediated epigenetic modification. However, little is known about the key proteins. Here, we report that the human PIWI-like family is a candidate protein that is involved in the pathway responsible for chromatin remodeling. The PIWI-like family proteins, expressed as the Flag-fusion proteins, formed a bulky body and localized to the nuclear periphery. Transient transfection of PIWI-like 4 (PIWIL4), only member of the PIWI-like family that was ubiquitously expressed in human tissues, induced histone H3 lysine 9 methylation at the p16(Ink4a) (CDKN2A) locus. The elevated level of histone methylation resulted in the downregulation of the p16(Ink4a) gene. These results suggest PIWIL4 plays important roles in the chromatin-modifying pathway in human somatic cells.