cDNA cloning, gene organization and expression analysis of human peptidylarginine deiminase type VI.

Peptidylarginine deiminase (PAD) catalyzes the post-translational modification of protein through the conversion of arginine to citrulline in the presence of calcium ions. Human, similar to rodents, has four isoforms of PAD (type I, II, III and IV/V), each of which is distinct in substrate specificity and tissue specific expression. In our large-scale sequencing project, we identified a new human PAD cDNA from a human fetal brain cDNA library. The putative protein encoded by this cDNA is designated hPADVI. Expression analysis of hPADVI showed that it is mainly expressed in adult human ovary and peripheral blood leukocytes. We conclude that hPADVI may be orthologous to mouse ePAD, basing on sequence comparison, chromosome localization and exon-intron structure analysis. PAD-mediated deimination of epithelial cell keratin resulting in cytoskeletal remodeling suggests a possible role for hPADVI in cytoskeletal reorganization in the egg and in early embryo development. This study describes a new important member of the human PAD family.

Comparative analysis of the mouse and human peptidylarginine deiminase gene clusters reveals highly conserved non-coding segments and a new human gene, PADI6.

Peptidylarginine deiminases (PADs) convert arginine residues in proteins into citrullines. They are suspected to be involved in multiple sclerosis and rheumatoid arthritis pathophysiology, and they play a role in epidermis homeostasis and possibly in regulation of gene expression through histone modification. In humans, four isoforms encoded by the genes PADI1-4 are known so far. We here report the characterization and comparative analysis of the human (355 kb) and mouse (240 kb) PAD gene clusters on chromosomes 1p35-36 and 4E1, respectively. We characterized an as yet unknown human PADI6 gene, and cloned the corresponding cDNA encoding a 694-amino-acid protein. RT-PCR analysis showed a rather restricted pattern of tissue-specific expression, mainly in ovary, testis and peripheral blood leukocytes. Nucleotide substitution rates suggest that PADI genes are under purifying selection. Comparative analysis of the human and mouse sequences identified 251 conserved non-coding segments predominantly clustered within the promoter regions, the large (>10 kb) first intron of each of the genes PADI1-3, and an 8 kb PADI1-2 intergenic region. The presence of numerous transcription factor binding sites suggests the segments are putative regulatory elements. This study is the first description of the human PADI6 gene and encoded protein, and the first step towards a better understanding of the coordinated regulation of PADI gene expression.