The Molecular Genetic Mechanism Of Heme Regulating The Expression Of Pancreatic Zymogen Genes

Heme is the prosthetic group for numerous proteins that play critical roles inoxygen delivery and charge transfer, such as hemoglobin, myoglobin and cytochromes.Heme also serves as a signaling molecule that modulates a number of molecular andcellular processes. Heme biosynthesis is a highly conserved pathway, which is catalyzedby a cascade of eight enzymatic reactions. Defects in the enzymes involved in the hemebiosynthetic pathway result in a group of human diseases known as porphyrias oranemia. Several studies on porphyrias have been reported, but some novel mechanismsof these diseases need to be further study.Previously, we established a UROD-deficient zebrafish (yquem/urod) as a modelfor studying human hepatoerythropoietic porphyria (HEP) and porphyria cutanea tarda(PCT),and reported downregulation of six pancreatic zymogen genes by microarray andreal-time PCR analyses. However, molecular genetic mechanisms underlying hemeregulation of these pancreatic zymogen genes are still unknown. So we perform the insitu hybridization and luciferase assays to investigate the molecular genetic mechanismsof heme regulating these pancreatic zymogen genes.The variegate porphyria (VP) model zebrafish and wild type zebrafish are used toperform the in situ hybridization and to analyze the expression pattern differencebetween them. A series of luciferase reporter vectors of pancreatic zymogen genes areconstructed and then transfected the NIH3T3cell line. We treat the cell line with heminat a special time and perform the luciferase assays in vitro to analyze the regulationmechanism by using the dual-report system.The in situ hybridization assays demostrate that the expression levels of pancreaticzymogen genes are down-regulated in the VP model zebrafish while hemin treatmentcan rescue the expression of these genes. Luciferase assays in vitro demonstrate thatMafK serves as dual-function transcription factor through exchanging its heterodimerization partners.When heterodimerize with Nrf2, MafK activates thesepancreatic zymogen genes; in contrast, when heterodimerize with Bach1, MafKrepresses these genes. These results provide a better understanding of the moleculargenetic mechanism of heme regulating the expression of pancreatic zymogen genes,shed new light on heme deficiency pathogenesis, and open novel approaches todiagnosing and treatment of patients with porphyria or pancreatic diseases.