MiRNA mediated interaction between leukaemia/lymphoma-related factor (LRF) and alternative splicing factor/splicing factor2 (ASF/SF2) affects MEF senescence and apoptosis.

LRF is a transcriptional repressor, which by recruiting histone deacetylases (HDAC) specifically represses p19/ARF expression, thus behaving as an oncogene. Conversely in MEF, LRF inhibition causes aberrant p19ARF upregulation resulting in proliferative defects and premature senescence. We have recently shown that LRF is controlled by microRNAs. Here we show that LRF acts on MEF proliferation and senescence/apoptosis by repressing miR-28 and miR-505, revealing a regulatory circuit where miRNAs work both upstream and downstream of LRF. By analyzing miRNA expression profiles of MEF transfected with LRF-specific short interfering RNAs, we found that miR-28 and miR-505 are modulated by LRF. Both miRNAs are predicted to target ASF/SF2, a serine/arginine protein essential for cell viability. In vertebrates, loss or inactivation of ASF/SF2 may result in genomic instability and induce G2 cell cycle arrest and apoptosis. We showed that miR-28 and miR-505 modulate ASF/SF2 by directly binding ASF/SF2 3'UTR. Decrease in LRF causes a decrease in ASF/SF2 which depends on up-regulation of miR-28 and miR-505. Alteration of each of the members of the LRF/miR-28/miR-505/ASF/SF2 axis affects MEF proliferation and the number of senescent and apoptotic cells. Consistently, the axis is coordinately modulated as cell senescence increases with passages in MEF culture. In conclusion, we show that LRF-dependent miRNAs miR-28 and miR-505 control MEF proliferation and survival by targeting ASF/SF2 and suggest a central role of LRF-related miRNAs, in addition to the role of LRF-dependent p53 control, in cellular homeostasis.