Alternative titles; symbols
HGNC Approved Gene Symbol: P4HA1
Cytogenetic location: 10q22.1 Genomic coordinates (GRCh38): 10:73,007,217-73,096,866 (from NCBI)
Prolyl 4-hydroxylase (EC 1.14.11.2) plays a central role in collagen synthesis. It catalyzes the formation of 4-hydroxyproline in collagens by hydroxylation of proline residues in peptide linkages. The 4-hydroxyproline residues are essential for the folding of the newly synthesized procollagen polypeptide chain into triple helical molecules. The active enzyme is a tetramer of 2 alpha and 2 beta subunits with a molecular weight of about 240,000. The beta subunit (P4HB; 176790) is identical to the enzyme disulfide isomerase (EC 5.3.4.1) and a major cellular thyroid-binding protein. The alpha subunit probably contributes a major part of the catalytic site of the enzyme. Helaakoski et al. (1989) isolated cDNA clones for the alpha subunit. They found that the clones encode a polypeptide of 517 amino acid residues and a signal peptide of 17 amino acids. Southern blot analyses of human genomic DNA with a cDNA probe for the alpha subunit suggested the presence of only 1 gene encoding 2 types of mRNA, which appear to result from mutually exclusive alternative splicing of primary transcripts of 1 gene.
Helaakoski et al. (1994) reported that the P4HA gene covers more than 69 kilobases and consists of 16 exons. Evidence had previously been presented for a mutually exclusive alternative splicing of RNA transcripts of the gene. The present data indicated that the mutually exclusive sequences found in the mRNAs are coded by 2 consecutive, homologous 71-bp exons, 9 and 10. These exons are identical in their first 5 basepairs and the overall identity between them is 61% at the nucleotide level and 58% at the level of the coded amino acids. Both types of mRNA were found to be expressed in all of the tissues studied, but in some tissues the type coding for the exon 9 or exon 10 sequences was more abundant than the other type.
By Southern blot analysis of rodent-human cell hybrids and by in situ hybridization, Pajunen et al. (1989) mapped the P4HA gene to chromosome 10q21.3-q23.1.
Helaakoski et al. (1995) and Annunen et al. (1997) demonstrated in the mouse and human, respectively, a second prolyl 4-hydroxylase alpha polypeptide, designated alpha(II); see P4HA2 (600608).
Friedman et al. (2000) found that the genome of C. elegans also possesses 2 genes that encode alpha subunits of prolyl 4-hydroxylase. The authors generated deletions within each gene to eliminate enzymatic activity. The deletion in one caused an aberrant body morphology, consistent with a role of prolyl 4-hydroxylase in formation of the body cuticle. The other mutant was phenotypically wildtype. However, the double mutant was not viable, suggesting an essential role for prolyl 4-hydroxylase that is normally accomplished by one gene or the other gene. The effects of the double mutation were mimicked by small-molecule inhibitors of prolyl 4-hydroxylase, validating the genetic results and suggesting that C. elegans can serve as a model system for the discovery of new inhibitors.
Teodoro et al. (2006) showed that p53 (191170) transcriptionally activates the alpha-2 collagen prolyl-4-hydroxylase gene, resulting in the extracellular release of antiangiogenic fragments of collagen types IV (see 120130) and XVIII (see 120328). Conditioned media from cells ectopically expressing either p53 or P4HA1 selectively inhibited growth of primary human endothelial cells. When expressed intracellularly or exogenously delivered, P4HA1 significantly inhibited tumor growth in mice. Teodoro et al. (2006) concluded that their results reveal a genetic and biochemical linkage between the p53 tumor suppressor pathway and the synthesis of antiangiogenic collagen fragments.
Qi et al. (2008) reported physical interactions between Ago2 (606229) and the alpha (P4H-alpha-1, P4HA1; 176710), and beta (P4H-beta) (P4HB; 176790) subunits of the type I collagen prolyl-4-hydroxylase (C-P4H-I). Mass spectrometric analysis identified hydroxylation of the endogenous Ago2 at proline-700. In vitro, both Ago2 and Ago4 (607356) seem to be more efficiently hydroxylated than Ago1 (606228) and Ago3 (607355) by recombinant human C-P4H-I. Human cells depleted of P4H-alpha-1 or P4H-beta by short hairpin RNA, and C-P4H-alpha-I-null mouse embryonic fibroblast cells, showed reduced stability of Ago2 and impaired short interfering RNA-programmed RISC activity. Furthermore, mutation of proline-700 to alanine also resulted in destabilization of Ago2, thus linking Ago2 P700 and hydroxylation at this residue to its stability regulation. Qi et al. (2008) concluded that their findings identified hydroxylation as a posttranslational modification important for Ago2 stability and effective RNA interference.
For discussion of a possible association between variation in the P4HA1 gene and a congenital disorder of connective tissue, see 176710.0001.
Holster et al. (2007) found that homozygous knockout of P4ha1 in mice caused embryonic lethality between embryonic day (E) 10.5 and E11.5. P4ha1 -/- embryos at E10.5 showed an 80% reduction in C-P4H activity compared with wildtype. Ultrastructural analysis revealed only rare contacts between the sparse mesenchymal cells in P4ha1 -/- embryos, and the cells had fewer filopodia compared with wildtype. P4ha1 -/- embryos appeared pale at E10.5, their capillary walls were frequently ruptured, and red blood cells were rarely detected in the lumen. Although they exhibited dilated endoplasmic reticulum, P4ha1 -/- cells were capable of synthesizing and secreting collagen IV, but it was not assembled into insoluble supramolecular structures in basement membranes.
In an 8-year-old Chinese boy with a congenital disorder of connective tissue, Zou et al. (2017) identified compound heterozygosity for 2 mutations in the P4HA1 gene: a 2-bp insertion (c.1323_1324insAG, NM_001017962.2) in exon 9, causing a frameshift predicted to result in a premature termination codon (Arg362GlyfsTer9), and a splice site mutation in intron 11 (c.1543+2T-G; 176710.0002), predicted to cause skipping of exon 12. In the same family, an affected fetus from a pregnancy that was terminated was also compound heterozygous for the mutations; the unaffected parents were each heterozygous for 1 of the mutations, neither of which was found in the dbSNP, NHLBI Exome Variant Server, or ExAC databases. The proband exhibited joint hypermobility, contractures, axial and appendicular hypotonia with congenital weakness, mild skeletal dysplasia without bone fragility, and high myopia. Both affected individuals had reduced collagen IV immunoreactivity at the muscle basement membrane. Analysis of patient dermal fibroblasts showed reduced P4AH1 protein levels and activity, as well as reduced thermal stability of collagen, compared to age-matched controls.
For discussion of the splice site mutation (c.1543+2T-G, NM_001017962.2) in intron 11 of the P4HA1 gene, predicted to cause skipping of exon 12, that was found in compound heterozygous state in a patient with a congenital disorder of connective tissue by Zou et al. (2017), see 176710.0001.
Annunen, P., Helaakoski, T., Myllyharju, J., Veijola, J., Pihlajaniemi, T., Kivirikko, K. I. Cloning of the human prolyl 4-hydroxylase alpha subunit isoform alpha(II) and characterization of the type II enzyme tetramer: the alpha(I) and alpha(II) subunits do not form a mixed alpha(I)alpha(II)beta2 tetramer. J. Biol. Chem. 272: 17342-17348, 1997. [PubMed: 9211872] [Full Text: https://doi.org/10.1074/jbc.272.28.17342]
Friedman, L., Higgin, J. J., Moulder, G., Barstead, R., Raines, R. T., Kimble, J. Prolyl 4-hydroxylase is required for viability and morphogenesis in Caenorhabditis elegans. Proc. Nat. Acad. Sci. 97: 4736-4741, 2000. [PubMed: 10781079] [Full Text: https://doi.org/10.1073/pnas.97.9.4736]
Helaakoski, T., Annunen, P., Vuori, K., MacNeil, I. A., Pihlajaniemi, T., Kivirikko, K. I. Cloning, baculovirus expression, and characterization of a second mouse prolyl 4-hydroxylase alpha-subunit isoform: formation of an alpha(2)beta(2) tetramer with the protein disulfide-isomerase/beta subunit. Proc. Nat. Acad. Sci. 92: 4427-4431, 1995. [PubMed: 7753822] [Full Text: https://doi.org/10.1073/pnas.92.10.4427]
Helaakoski, T., Veijola, J., Vuori, K., Rehn, M., Chow, L. T., Taillon-Miller, P., Kivirikko, K. I., Pihlajaniemi, T. Structure and expression of the human gene for the alpha subunit of prolyl 4-hydroxylase: the two alternatively spliced types of mRNA correspond to two homologous exons the sequences of which are expressed in a variety of tissues. J. Biol. Chem. 269: 27847-27854, 1994. [PubMed: 7961714]
Helaakoski, T., Vuori, K., Myllyla, R., Kivirikko, K. I., Pihlajaniemi, T. Molecular cloning of the alpha-subunit of human prolyl 4-hydroxylase: the complete cDNA-derived amino acid sequence and evidence for alternative splicing of RNA transcripts. Proc. Nat. Acad. Sci. 86: 4392-4396, 1989. [PubMed: 2543975] [Full Text: https://doi.org/10.1073/pnas.86.12.4392]
Holster, T., Pakkanen, O., Soininen, R., Sormunen, R., Nokelainen, M., Kivirikko, K. I., Myllyharju, J. Loss of assembly of the main basement membrane collagen, type IV, but not fibril-forming collagens and embryonic death in collagen prolyl 4-hydroxylase I null mice. J. Biol. Chem. 282: 2512-2519, 2007. [PubMed: 17135260] [Full Text: https://doi.org/10.1074/jbc.M606608200]
Pajunen, L., Jones, T. A., Helaakoski, T., Pihlajaniemi, T., Solomon, E., Sheer, D., Kivirikko, K. I. Assignment of the gene coding for the alpha-subunit of prolyl 4-hydroxylase to human chromosome region 10q21.3-23.1. Am. J. Hum. Genet. 45: 829-834, 1989. [PubMed: 2556027]
Qi, H. H., Ongusaha, P. P., Myllyharju, J., Cheng, D., Pakkanen, O., Shi, Y., Lee, S. W., Peng, J., Shi, Y. Prolyl 4-hydroxylation regulates Argonaute 2 stability. Nature 455: 421-424, 2008. [PubMed: 18690212] [Full Text: https://doi.org/10.1038/nature07186]
Teodoro, J. G., Parker, A. E., Zhu, X., Green, M. R. p53-mediated inhibition of angiogenesis through up-regulation of a collagen prolyl hydroxylase. Science 313: 968-971, 2006. [PubMed: 16917063] [Full Text: https://doi.org/10.1126/science.1126391]
Zou, Y., Donkervoort, S., Salo, A. M., Foley, A. R., Barnes, A. M., Hu, Y., Makareeva, E., Leach, M. E., Mohassel, P., Dastgir, J., Deardorff, M. A., Cohn, R. D., DiNonno, W. O., Malfait, F., Lek, M., Leikin, S., Marini, J. C., Myllyharju, J., Bonnemann, C. G. P4HA1 mutations cause a unique congenital disorder of connective tissue involving tendon, bone, muscle and the eye. Hum. Molec. Genet. 26: 2207-2217, 2017. [PubMed: 28419360] [Full Text: https://doi.org/10.1093/hmg/ddx110]