Fusagene vectors: a novel strategy for the expression of multiple genes from a single cistron

Transduction of cells with multiple genes, allowing their stable and co-ordinated expression, is difficult with the available methodologies. A method has been developed for expression of multiple gene products, as fusion proteins, from a single cistron. The encoded proteins are post-synthetically cleaved and processed into each of their constituent proteins as individual, biologically active factors. Specifically, linkers encoding cleavage sites for the Golgi expressed endoprotease, furin, have been incorporated between in-frame cDNA sequences encoding different secreted or membrane bound proteins. With this strategy we have developed expression vectors encoding multiple proteins (IL-2 and B7.1, IL-4 and B7.1, IL-4 and IL-2, IL-12 p40 and p35, and IL-12 p40, p35 and IL-2 ). Transduction and analysis of over 100 individual clones, derived from murine and human tumour cell lines, demonstrate the efficient expression and biological activity of each of the encoded proteins. Fusagene vectors enable the co-ordinated expression of multiple gene products from a single, monocistronic, expression cassette.

D-hydroxyacyl-CoA dehydrogenase deficiency. Identification of a new peroxisomal disorder with implications for other disorders of beta-oxidation

The second and third steps of peroxisomal beta-oxidation are catalysed by two multifunctional enzymes: D-bifunctional protein and L-bifunctional protein. Here we show that fibroblasts of a patient described as being deficient in the 3-hydroxyacyl-CoA dehydrogenase component of D-bifunctional protein and fibroblasts of a patient described as being deficient in L-bifunctional protein do not complement one another. Using a newly developed method to measure the activity of D-bifunctional protein in fibroblast homogenates, we found that the activity of the D-bifunctional protein was completely deficient in the patient with presumed L-bifunctional protein deficiency.

Peroxisomal fatty acid oxidation disorders and 58 kDa sterol carrier protein X (SCPx). Activity measurements in liver and fibroblasts using a newly developed method

Sterol carrier protein X (SCPx) plays a crucial role in the peroxisomal oxidation of branched-chain fatty acids. To investigate whether patients with an unresolved defect in peroxisomal beta-oxidation are deficient for SCPx, we developed a novel and specific assay to measure the activity of SCPx in both liver and fibroblast homogenates. The substrate used in the assay, 3alpha, 7alpha,12alpha-trihydroxy-24-keto-5beta-cholestanoy l-CoA (24-keto-THC-CoA), is produced by preincubating the enoyl-CoA of the bile acid intermediate THCA with a lysate from the yeast Saccharomyces cerevisiae expressing human D-bifunctional protein. After the preincubation period, liver or fibroblast homogenate is added plus CoASH, and the production of choloyl-CoA is determined by HPLC. The specificity of the assay was demonstrated by the finding of a full deficiency in fibroblasts from an SCPx knock-out mouse. In addition to SCPx activity measurements in fibroblasts from patients with a defect in peroxisomal beta-oxidation of unresolved etiology, we studied the stability and activity of SCPx in fibroblasts from patients with Zellweger syndrome, which lack functional peroxisomes. We found that SCPx is not only stable in the cytosol, but displays a higher activity in fibroblasts from patients with Zellweger syndrome than in control fibroblasts. Furthermore, in all patients studied with a defect in peroxisomal beta-oxidation of unknown origin, SCPx was found to be normally active, indicating that human SCPx deficiency remains to be identified.

Peroxisomal bifunctional protein deficiency revisited: resolution of its true enzymatic and molecular basis

In the past few years, many patients have been described who have a defect of unknown origin in the peroxisomal beta-oxidation pathway. Complementation analysis has been done by various groups to establish the extent of the genetic heterogeneity among the patients. These studies were based on the use of two established cell lines, one with a deficiency of acyl-CoA oxidase and one with a deficiency of l-bifunctional protein (l-BP), and they showed that most patients belong to the l-BP-deficient group. However, molecular analysis of the cDNA encoding l-BP in patients failed to show any mutations. The recent identification of a new d-specific bifunctional protein (d-BP) prompted us to reinvestigate the original patient with presumed l-BP deficiency. In a collaborative effort, we have now found that the true defect in this patient is at the level of the d-BP and not at the level of the l-BP. Our results suggest that most, if not all, patients whose condition has been diagnosed as l-BP are, in fact, d-BP deficient. We tested this hypothesis in nine patients whose condition was diagnosed as l-BP deficiency on the basis of complementation analysis and found clear-cut mutations in the d-BP cDNA from all patients.

Peroxisomal D-hydroxyacyl-CoA dehydrogenase deficiency: resolution of the enzyme defect and its molecular basis in bifunctional protein deficiency

Peroxisomes play an essential role in a number of different metabolic pathways, including the beta-oxidation of a distinct set of fatty acids and fatty acid derivatives. The importance of the peroxisomal beta-oxidation system in humans is made apparent by the existence of a group of inherited diseases in which peroxisomal beta-oxidation is impaired. This includes X-linked adrenoleukodystrophy and other disorders with a defined defect. On the other hand, many patients have been described with a defect in peroxisomal beta-oxidation of unknown etiology. Resolution of the defects in these patients requires the elucidation of the enzymatic organization of the peroxisomal beta-oxidation system. Importantly, a new peroxisomal beta-oxidation enzyme was recently described called D-bifunctional protein with enoyl-CoA hydratase and 3-hydroxyacyl-CoA dehydrogenase activity primarily reacting with alpha-methyl fatty acids like pristanic acid and di- and trihydroxycholestanoic acid. In this patient we describe the first case of D-bifunctional protein deficiency as resolved by enzyme activity measurements and mutation analysis. The mutation found (Gly16Ser) is in the dehydrogenase coding part of the gene in an important loop of the Rossman fold forming the NAD+-binding site. The results show that the newly identified D-bifunctional protein plays an essential role in the peroxisomal beta-oxidation pathway that cannot be compensated for by the L-specific bifunctional protein.