Differential Effects of Protein Kinase C Inhibitors on Nuclear and Cytoplasmic DMPK Transcript Dynamics in Myotonic Dystrophy Type 1 Cells

The major molecular basis for myotonic dystrophy type 1 disorder is the occurrence of a mutation leading to expanded CTG triplet units in the 3’-untranslated region of Dystrophia Myotonica Protein Kinase (DMPK) gene, which leads to the formation of foci in the nuclei of these cells. An assay based on the DMPK transcript (Bpm I polymorphism) was developed to test the effect of compounds of protein Kinase C inhibitors- hypericin and Ro 31-8220- to determine whether either inhibitor affected the transport of DMPK transcripts from nucleus to the cytoplasm or reduced the proportion of the transcript in both fibroblast and myoblast cells. The results from this study showed that the protein kinase C inhibitors were not able to affect the relocation of mutant DMPK transcripts from the nucleus to the cytoplasm in both DM1 fibroblasts and myoblasts, but Ro 31-8220 significantly reduced mutant transcripts in the nuclear fraction of DM1 fibroblasts. In the nuclei of fibroblasts, Ro 31-8220 treatment showed a 38.5±5.4% proportion of mutant transcript, hypericin treatment exhibited 54.2±3.5% mutant transcript, while those of DMSO treatment and untreated were 43.7±3.0% and 51.4±0.8%, respectively. For cytoplasmic fractions of DM1 fibroblasts, Ro 31-8220-treated cells indicated 94.4±1.7% normal transcript, hypericin treatment showed 91.6±1.0%, with DMSO-treated and untreated cells having 90.0±1.9% ad 89.5±2.3%, respectively. In the DM1 myoblasts nuclear fraction, 61.8±1.7% mutant transcript was observed in Ro 31-8820- treated cells, 67.5±2.8% mutant transcript occurred in hypericin treatment, while DMSO treatment and untreated cells had 52.4±1.7% and 48.7±0.8%, respectively. In myoblast cytoplasmic fractions, hypericin and Ro 31-8220 showed 90.6±2.7% and 80.8±0.3% normal transcripts, respectively, with DMSO treatment showing 81.1±0.5% normal transcript, while the untreated showed 80.0±5.7% normal transcript. This study has discovered the role of Ro 31-8220 in reducing the proportion of mutant transcripts I nuclear fraction while increasing the levels of the normal transcripts was increased in the cytoplasmic fraction of DM1 cells. Taken together, results from this study suggest that Ro 31-8220 may have therapeutic potential for reducing mutant DMPK transcript levels with potential therapeutic value