Loss of Lamin A leads to the nuclear translocation of AGO2 and compromised RNA interference
In mammals, RNA interference (RNAi) was historically studied as a cytoplasmic event, however, in the last decade growing number of reports convincingly show nuclear localization of the AGO proteins.  Nevertheless, the mechanism and the extent of nuclear RNAi remains to be fully elucidated. We found that reduced Lamin A levels significantly induced nuclear influx of AGO2 in SHSY5Y neuroblastoma and A375 melanoma cancer cell lines, which normally have no nuclear AGO2. Lamin A KO manifested a more pronounced effect in SHSY5Y cells compared to A375 evident by changes in cell morphology, increased cell proliferation and oncogenic miRNA expression. Furthermore, in SHSY5Y cells, AGO fPAR-CLIP in Lamin A KO cells revealed significantly reduced activity of RNAi. Further exploration of the nuclear AGO interactome by mass spectrometry indicated that AGO2 is in complex with FAM120A, an RNA binding protein and known interactor of AGO2. By performing FAM120A fPAR-CLIP we discovered that FAM120A co-binds AGO targets and that this competition reduces the activity of RNAi. Therefore, loss of Lamin A triggers nuclear AGO2 translocation, RNAi impairment and selective upregulation of oncogenic miRNAs to facilitate cancer cell proliferation. Overall design: We performed AGO fPAR-CLIP to assess AGO proteins occupancy on RNA transcripts in SHSY5Y and A375 WT and Lamin A KO cells from either the cytoplasmic or nuclear fractions. FAM120A  fPAR-CLIP was carried out in SHSY5Y and A375 Lamin A KO cells from either the cytoplasmic or nuclear fractions.