Protein arginine methyltransferase 5 is a key regulator of the MYCN oncoprotein in neuroblastoma cells.
Bottom Line: Immunoblotting of NB cell-lines shows that high PRMT5 expression is strongly associated with MYCN-amplification (P < 0.004, Mann-Whitney U-test) and immunohistochemical analysis of primary NBs reveals that whilst PRMT5 protein is ubiquitously expressed in the cytoplasm of most cells, MYCN-amplified tumours exhibit pronounced nuclear PRMT5 staining.PRMT5 knockdown in MYCN-overexpressing cells, including the SHEP-21N cell-line with inducible MYCN expression leads to a dramatic decrease in MYCN protein and MYCN-associated cell-death in SHEP-21N cells.Together our studies implicate PRMT5 in a novel mode of MYCN post-translational regulation and suggest PRMT5 plays a major role in NB tumorigenesis.
Affiliation: Cancer Epigenetics Laboratory University of Bristol, Bristol BS8 1TD, UK.Show MeSH
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Mentions: To further investigate the strong association between PRMT5 and MYCN status, we next examined the effect of PRMT5 knockdown on MYCN in SK-N-BE(2)C, NGP and Kelly cell-lines, all of which have MYCN amplification. As shown in Figure 4A, PRMT5 depletion was accompanied by a dramatic decrease of MYCN protein with two independent PRMT5 siRNAs, thereby negating the possibility of off-target effects. Notably, the PRMT5-dependent MYCN decrease in NGP cells suggests an alternative mechanism for PRMT5 compared to the BET domain inhibitor JQ-1, which did not affect MYCN in NGP cells (Puissant et al., 2013). MYCN transcript levels were only moderately decreased accompanying PRMT5 knockdown (Figure S4B), suggesting that PRMT5 mediates MYCN regulation at post-transcriptional levels, although we cannot currently exclude composite effects including indirect transcriptional regulation, for example by PRMT5 depletion leading to reactivation of epigenetically silenced MYCN repressor proteins or microRNAs.
Affiliation: Cancer Epigenetics Laboratory University of Bristol, Bristol BS8 1TD, UK.