Erythropoietic protoporphyria (EPP) results from partial deficiency of
ferrochelatase (FECH). Genetically, EPP patients differ from asymptomatic mutation carriers at the unmutated FECH allele, the expression of which is modulated by single nucleotide polymorphism IVS3-48C/T. The IVS3-48C genotype, which is present among patients, leads to correct splicing of 60% of the
pre-mRNA and to alternative splicing of 40%, the latter
mRNA-product being destroyed by nonsense-mediated decay. An IVS3-48T genotype generates 80% correct and 20% aberrant products. Our study demonstrated that under
iron deficient conditions, the aberrant splice product was increased to 56% and 50% of total FECH
mRNA in erythroleukemic K562 and lymphoblastoid cell lines, respectively, both being homozygous for IVS3-48T. Concomitantly, FECH
protein was decreased.
Iron deficiency had less effect on the FECH splice ratio in an IVS3-48C/C lymphoblastoid cell line. Effects similar to
iron deficiency were generated by
siRNA knockdown of either
splicing factor U2AF(65) or Fe(II)- and 2-oxoglutarate-dependent
dioxygenase Jumonji domain-containing
protein 6 (Jmjd6), which interacts with
U2AF(65) by lysyl-hydroxylation. Based on these results, we propose that the availability of
iron, a co-factor of Jmjd6, modulates U2AF(65)-lysyl-hydroxylation. This in turn, influences the relative amounts of correct and aberrant FECH
mRNA splice products and thus, regulates the FECH
enzyme activity.