CONTRASTING EFFECTS OF PNA INVASION OF THE CHIMERIC DMMYC GENE ON TRANSCRIPTION OF ITS MYC AND PVT DOMAINS

A peptide nucleic acid (PNA) complementary to a unique DNA sequence in the second exon of the human myc proto-oncogene was tested for its ef fects on transcription in colonic adenocarcinoma cells in which myc ha d been amplified and rearranged. A prominent rearrangement in this hum an cell line (COLO320-DM) involves the insertion of exon 1 of the PVT gene, which is normally located 57 kb downstream, into the first myc i ntron. We compared the effects of PNA invasion of the resulting chimer ic gene (DMMYC) on sense and antisense transcription of its myc and PV T domains. Run-on transcription experiments showed that PNA binding to the unique myc sequence was highly specific and strongly inhibited se nse transcription of four unique myc sequences downstream of the PNA D NA hybridization site, the extent of inhibition at each sequence depen ding on the duration of exposure to PNA, and the distance between the downstream myc sequence and the PNA block. The same PNA also inhibited antisense transcription of unique myc sequences upstream of the bindi ng site, confirming that transit of the RNA polymerase II complexes wa s impaired in both directions. The inhibitory effect of PNA on upstrea m antisense transcription extended beyond the recombination site into the contiguous PVT domain of the chimeric DMMYC gene. In contrast, the same PNA did not inhibit PVT transcription in a cell line (Raji lymph oma) in which PVT rearranegement did not involve the myc locus.