Pterin-4a-carbinolamine Dehydratase Research Articles

Overexpression of Pterin-4a-carbinolamine Dehydratase/Dimerization Cofactor of Hepatocyte Nuclear Factor 1 in Human Colon Cancer

Pterin-4a-carbinolamine dehydratase (PCD) is a bifunctional protein also known as DCoH (dimerization co-factor of hepatocyte nuclear factor 1 (HNF1)). PCD/DCoH modulates the DNA binding specificity of HNF1, thus acting on its transcriptional activity. In addition, it participates in the recycling of tetrahydrobiopterin (BH(4)), an essential cofactor of several metabolic reactions. We investigated colorectal tumors and colorectal tumor cell lines as compared to normal colon samples in search of a potential differential expression of PCD/DCoH. Immunohistochemistry was conducted on 20 human colorectal tumors and 20 normal samples using a specific polyclonal antibody. Immunoblotting and RT-PCR analysis for PCD/DCoH and HNF1 were also performed on both human tissues and CACO-2 and HT-29 cell lines. All of the 20 tumors and both colon cancer cell lines presented a strong and widespread immunoreactivity for PCD/DCoH, contrasting with the absence of expression in the normal epithelia. We thus report the massive overexpression of PCD/DCoH in colon tumors, which is in striking contrast with the absence of staining in normal counterparts. The sharp contrast in the expression of a modulator of transcriptional activity between tumoral and normal cells may have a physiopathological role. PCD/DCoH could potentially be a new marker of malignant colon cells in vivo.

Hyperphenylalaninemia with High Levels of 7-Biopterin is Associated with Mutations in the PCBD Gene Encoding the Bifunctional Protein Pterin-4a-Carbinolamine Dehydratase and Transcriptional Coactivator (DCoH)

Pterin-4a-carbinolamine dehydratase (PCD) is required for efficient tetrahydrobiopterin regeneration after phenylalanine hydroxylase activity. This catalytic function was proposed to be specifically defective in newborns with a mild form of hyperphenylalaninemia (HPA) and persistent high urinary levels of primapterin (7-biopterin). A second regulatory task of the same protein is DCoH, a coactivation of transcription by hepatocyte nuclear factor 1alpha (HNF-1alpha), a function that is apparently not impaired in these HPA individuals. It has been shown elsewhere that the human PCD/DCoH bifunctional protein is encoded by a single 4-exon-containing gene, PCBD, located on chromosome 10q22. We have now examined the PCBD gene for mutations at the genomic level in six such HPA patients from four different families. By the use of new intron-specific primers, we detected, in all six patients, single, homozygous nucleotide alterations, in exon 4, that were inherited from their parents. These homozygous alterations predicted mutant PCD/DCoH with a single amino acid exchange, in two cases (alleles T78I), or premature stop codons, in the other four patients (alleles E86X and Q97X). Recombinant expression in Escherichia coli revealed that the mutant proteins-T78I, E86X, and Q97X-are almost entirely in the insoluble fraction, in contrast to wild type, which is expressed as a soluble protein. These data support the proposal that HPA in combination with urinary primapterin may be due to autosomal recessive inheritance of mutations in the PCBD gene specifically affecting the dehydratase activity.

Spectroscopic characterization of human liver pterin 4a-carbinolamine dehydratase.

The hepatic hydroxylation of phenylalanine catalyzed by phenylalanine hydroxylase (PAH), is dependent on tetrahydrobiopterin (BH4) and two additional enzymes, pterin 4a-carbinolamine dehydratase (PCD) and dihydropterin reductase (1). PCD, previously named “phenylalanine hydroxylase stimulating protein”, catalyzed the conversion of 4a-OH BH4, an intermediate product in hydroxylation reaction, to quinonoid dihydrobiopterin and water (3). It was proposed that PCD play a key role in preventing the formation of 7-pterins which are characteristic for primapterinuria, a new variant form of hyperphenylalaniemia (4,5). The PCD was purified from rat and human liver and partially characterized (2,6). The primary structure of purified enzyme was determined and it was been found that PCD is identical to a homeodomein-containing protein involved in regulation of transcription (7). These facts suggest on a double role of the dehydratase in the cell. In present work we undertook the further characterization of PCD by means of fluorescence spectroscopy.