PPHLN1 (periphilin 1) is an RNA-binding component of the HUSH (Human Silencing Hub) complex, a multiprotein epigenetic silencing machinery that represses mobile genetic elements including retroviruses and transposable elements 12. Within the HUSH complex, PPHLN1 functions alongside core components TASOR and MPP8 to maintain transcriptional silencing through recruitment to H3K9me3-rich genomic loci and subsequent promotion of SETDB1-mediated histone methylation 1. The protein specifically binds nascent transcripts of mobile genetic elements, enabling HUSH-dependent silencing mechanisms 2. PPHLN1 contributes to silencing unintegrated retroviral DNA that remains extrachromosomal after infection, working with NP220 and other silencing factors 2. The HUSH complex, including PPHLN1, shows striking colocalization with PRC1.6 components on chr12, particularly at active promoters, suggesting broader roles in transcriptional regulation 3. Clinically, PPHLN1 has oncogenic relevance through fusion proteins with FGFR2 in intrahepatic cholangiocarcinoma, where FGFR2-PPHLN1 fusions create constitutively active kinases that drive tumorigenesis 4. Additionally, PPHLN1 splicing regulation by OTX2 maintains stem cell programs in group 3 medulloblastoma 5.