Isolated cytochrome c oxidase deficiency as a cause of MELAS.

BACKGROUND: MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes) is one of the more common mitochondrial encephalomyopathies. About 80% of MELAS cases are caused by transition 3243A-->G in the mitochondrial tRNA(Leu(UUR)) gene (MT-TL1). Other mutations in MT-TL1, other mitochondrial tRNA genes and mitochondrial-encoded subunits of respiratory complex I account for the remainder of cases. OBJECTIVE: To characterise the molecular basis of a MELAS case without a mutation in any recognised MELAS target gene. RESULTS AND METHODS: Deletion of a single nucleotide (7630delT) within MT-CO2, the gene of subunit II of cytochrome c oxidase (COX), was identified by mitochondrial DNA (mtDNA) sequencing. The deletion-induced frameshift results in a stop codon close to the 5' end of the reading frame. The lack of subunit II (COII) precludes the assembly of COX and leads to the degradation of unassembled subunits, even those not directly affected by the mutation. Despite mitochondrial proliferation and transcriptional upregulation of nuclear and mtDNA-encoded COX genes (including MT-CO2), a severe COX deficiency was found with all investigations of the muscle biopsy (histochemistry, biochemistry, immunoblotting). CONCLUSIONS: The 7630delT mutation in MT-CO2 leads to a lack of COII with subsequent misassembly and degradation of respiratory complex IV despite transcriptional upregulation of its subunits. The causal association of the resulting isolated COX deficiency with MELAS is at odds with current concepts of the biochemical deficits underlying this common mitochondrial disease, and indicates that the genetic and pathobiochemical heterogeneity of MELAS is greater than previously appreciated.

Growth inhibition by dehydrothyrsiferol - a non-Pgp modulator, derived from a marine red alga - in human breast cancer cell lines.

The novel marine terpenoid dehydrothyrsiferol (DHT) has been isolated from a Canarian red alga Laurencia viridis sp. nov (Ceramiales, Rhodomelaceae) (1). Its cytotoxicity against three human breast cancer cell lines, namely T47D, ZR-75-1, and Hs578T was examined and compared with the chemotherapeutic compound doxorubicin and the mitosis-inhibitor colchicine. Primary breast carcinomas exhibit MDR1 gene expression (3). As the investigated mammary cell lines did not exhibit rhodamine 123 efflux we proved in a P-glycoprotein (Pgp) overexpressing human epidermoid cancer cell line that the marine metabolite does not modulate Pgp mediated drug transport. Therefore, it could be used in Pgp expressing cancer cells without interference.

Inhibitory effects of a novel marine terpenoid on sensitive and multidrug resistant KB cell lines.

Mechanisms of growth inhibition by the novel marine compound dehydrothyrsiferol (DHT) were investigated in a sensitive and an MDR+ human epidermoid cancer cell line. DHT was found to circumvent multidrug resistance mediated by P-glycoprotein. Cell cycle analysis revealed an accumulation in S-phase. The anchorage independent clonogenic growth in soft agar was not significantly reduced at IC50 concentrations. Reduced cell growth caused by induction of apoptotic or necrotic cell death could not be verified. Therefore, cell proliferation during an incubation period of five days was measured and found to be significantly reduced. We conclude that growth inhibition by dehydrothyrsiferol in KB cancer cells is not mediated by apoptosis but by growth retardation; the reasons for this are worth being investigated in detail.