The specific function of myotonic dystrophy protein kinase (DMPK) is still not known. We found that overexpression of human DMPK in C2C12 myogenic culture induces the expression of ferritin heavy chain (FN-H) mRNA using differential display analysis. The quantity of FN-H mRNA was greater in the DMPK transfectant with five CTG triplet repeats in the 3'-untranslated region, while it was lower in the transfectant with 46 CTG repeats, over that of the control clone. We also investigated the quantity of interleukin 1-alpha (IL-1alpha) mRNA in each culture, due to the fact that this cytokine is able to induce FN-H expression, regardless of the concentration of free iron. Quantitative, competitive polymerase chain reaction (PCR) analysis revealed that the quantity of IL1-alpha mRNA is higher in the transfectant with five repeats, compared to the quantity of mRNA in the control clone; however, it is markedly lower in the clone with 46 repeats. These results suggest that overexpression of DMPK in C2C12 cultures may up-regulate IL-1alpha expression, resulting in the induction of FN-H expression. However, a large number of CTG repeats in the 3'-untranslated region of the DMPK gene may affect the pathway of IL-1alpha transcription, thereby resulting in decreased expression of FN-H.