PARP1 negatively regulates MAPK signaling by impairing BRAF-X1 translation

In human cells BRAF oncogene is invariably expressed as a mix of two coding transcripts: BRAF-ref and BRAF-X1 . These two mRNA isoforms, remarkably different in the sequence and length of their 3′UTRs , are potentially involved in distinct post-transcriptional regulatory circuits. Herein, we identify PARP1 among the mRNA Binding Proteins that specifically target the X1 3′UTR in melanoma cells. Mechanistically, PARP1 Zinc Finger domain down-regulates BRAF expression at the translational level. As a consequence, it exerts a negative impact on MAPK pathway, and sensitizes melanoma cells to BRAF and MEK inhibitors, both in vitro and in vivo. In summary, our study unveils PARP1 as a negative regulator of the highly oncogenic MAPK pathway in melanoma, through the modulation of BRAF - X1 expression.