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: In neuronal progenitor cells, MYCN is proteosomally regulated during mitosis (Sjostrom et al., 2005), so we investigated whether the PRMT5-depletion effect on MYCN might be indirect and attributable to solely to G1 cell-cycle arrest. Whilst a degree of G1 arrest was apparent in NGP and Kelly cells after PRMT5 knockdown, it was below statistical significance (Figure 6A and B). Furthermore, G1 arrest was not observed after PRMT5 knockdown in SHEP-Tet21N cells overexpressing MYCN, in contrast to uninduced SHEP-Tet21N cells where G1 arrest was pronounced (Figure 6C). Interestingly however, MYCN-induced SHEP-Tet21N cells exhibited a significant decrease of cells in G2/M-phase after PRMT5 knockdown (P < 0.005), concomitant with an increase of cells in S-phase. A similar effect on S-phase has been demonstrated for c-myc in medulloblastoma cells (Zhang et al., 2006). Together these experiments strongly support PRMT5 being able to directly influence MYCN protein stability and modulate its biological activities.
Affiliation: Cancer Epigenetics Laboratory University of Bristol, Bristol BS8 1TD, UK.