The novel heme-dependent inducible protein, SRRD regulates heme biosynthesis and circadian rhythms.

Heme plays a role in the regulation of the expression of genes related to circadian rhythms and heme metabolism. In order to identify new heme-regulated proteins, an RNA sequence analysis using mouse NIH3T3 cells treated without or with 5-aminolevulinic acid (ALA) was performed. Among the changes observed in the levels of various mRNAs including heme oxygenase-1 (HO-1) and ALA synthase-1 (ALAS1), a mouse homologue of the plant circadian-regulating protein SRR1, SRR1 domain containing (SRRD) was induced by the ALA treatment. The expression of SRRD was dependent on heme biosynthesis, and increased the production of heme. SRRD was expressed under circadian rhythms, and influenced the expression of clock genes including PER2, BMAL1, and CLOCK. The knockout of SRRD arrested the growth of cells, indicating that SRRD plays roles in heme-regulated circadian rhythms and cell proliferation.

p53 directly regulates the transcription of the human frataxin gene and its lack of regulation in tumor cells decreases the utilization of mitochondrial iron.

Mitochondrial frataxin functions in iron homeostasis, biogenesis of iron-sulfur clusters, protection from oxidative stress and apoptosis, and as a tumor suppressor protein. We examined regulation of the expression of the human frataxin by p53. Pifithrin-α, an inhibitor of p53 function, and knockdown of p53 decreased the level of frataxin mRNA in human kidney HEK 293T cells. The transcriptional activity of the human frataxin gene is enhanced by the proximal promoter containing the p53-responsive element (p53RE) on the gene. Chromatin immunoprecipitation assay and electrophoretic mobility shift assay confirmed the binding of p53 to the human frataxin p53RE. The expression of wild-type p53 in human cancer HeLa cells increased the reporter activity carrying p53RE at the region of -209 to -200bp of the frataxin promoter. Finally, when the HeLa cells overexpressing frataxin were treated with 5-aminolevulinic acid (ALA), there was less accumulation of protoporphyrin than HeLa control cells, and it was sharply decreased by the addition of iron citrate, suggesting that the utilization of mitochondrial iron for heme biosynthesis can be dependent on the level of frataxin. Alternatively, the low expression of frataxin not regulated by p53 in tumor cells lowers the utilization of iron in mitochondria, causing the tumor-specific ALA-induced accumulation of protoporphyrin.

Congenital Erythropoietic Porphyria: Mutation of the Uroporphyrinogen III Cosynthase Gene in a Vietnamese Patient.

Congenital erythropoietic porphyria (CEP) arises from an autosomal recessive inherited disorder of the porphyrin metabolism, which leads to the accumulation of uroporphyrinogen I in bone marrow, skin and several other tissues by a deficiency of uroporphyrinogen III cosynthase (UROS). We studied a Vietnamese patient and her family suffering from severe cutaneous photosensitivity with skin fragility, bullous lesions and hypertrichosis on light-exposed areas. A missense mutation in the UROS gene was identified as a transversion of G to T at nucleotide 11,776, resulting in a substitution of valine by phenylalanine at codon 3 of exon 2. The patient showed a homozygous mutant profile, and the heterozygous state was observed in the parents. The activity of mutated UROS expressed in Escherichia coli was less than 16.1% that of the control, indicating that the markedly reduced activity of UROS is responsible for CEP. We described for the first time a mutation in the UROS gene in a Southeast Asian patient and a molecular diagnosis for the identification of clinically asymptomatic heterozygous mutation carriers and families with CEP.