ARMH1

Armadillo-like Helical Domain Containing 1 (ARMH1) is a protein which in humans is encoded by chromosome 1 open reading frame 228, also known as the ARMH1 gene. The gene shows expression levels significantly higher in bone marrow, lymph nodes, and testis. Currently the function of the gene and subsequent protein is still uncertain.

Gene

The ARMH1 gene is found on the plus strand of chromosome 1 between base pairs 45,140,361 and 45,191,784. Other known aliases include P40, NCRNA00082, and most commonly C1orf228. The gene has 13 exons, most of which are concentrated near the poly-A site at the end of the gene and two located upstream from the start codon. The gene is highly expressed in bone marrow and lymph nodes, suggesting an immunological function.

Gene expression

RNA seq data was produced using multiple samples of human tissues at varying stages of development. One study was acquired from 20 separate samples of human tissue showing significantly more expression of ARMH1 in the thymus, trachea, and lungs. A second study shows 27 different tissues samples in 95 different individual subjects. The expression levels are significantly higher in bone marrow, lymph nodes, and testis. A third shows high expression in white blood cells and testis again, corroborating previous studies. A temporal study focused on expression in different stages of development collected 35 human fetal samples, from 6 distinct tissues, between 10 and 20 weeks gestational time and sequenced using Illumina TruSeq Stranded Total RNA. The data slightly favored expression in the adrenal glands throughout development. In each of the other tissues there were no stark changes in expression through time, only a small decline of gene expression as development furthers.

Gene transcripts

The ARMH1 gene has extensive abilities to alter its function and size through isoforms. Gene isoforms are mRNAs that are produced from the same locus but are different in their transcription start sites, protein coding DNA sequences and/or untranslated regions, potentially altering gene function. All known isoforms are organized and listed below with information gathered from NCBI gene, and a Bioinformatics tool for calculating molecular weight.

mRNA

The mRNA for this gene can be spliced in many different ways, making way for approximately 20 known isoforms. The most common mRNA gets spliced down to a coding region that is about 1693 nucleotides long which makes up 440 amino acids in total. In a comprehensive study on oral squamous cell carcinoma, the sixth most prevalent cancer worldwide, identified ARMH1 as a gene of interest by comparing healthy subjects mRNA against affected individuals. Through mRNA inhibition of ARMH1, researchers demonstrated significantly reduced leukemic cell proliferation (P=.0041) and leukemic cell migration (P=.0001), as well as a decreased resistance to the chemotherapy drug Cytarabine.

Protein

The protein encoded by the gene goes by the same name, Armadillo like containing helical domain 1. The isoelectric point of the ARMH1 protein is around a pH of 5.5. The protein has 2 known major domains, one being a transmembrane domain and the other being a coiled coil. Within the coiled coil domains, the ARMH1 protein has 24 alpha helices. The European Bioinformatics Institute's analysis of ARMH1 reveals clearly a significantly enriched lysine content as well as a significantly deficient proline count. The protein has been proven to have one major interaction with the human protein known as ABAT. Gamma-aminobutyric acid transaminase (ABAT) catalyzes the conversion of gamma-aminobutyric acid (GABA) into succinic semialdehyde. Additionally, ABAT expression was associated with glycolysis-related genes, infiltrated immune cells, immunoinhibitors, and immunostimulators in HCC.

Homology and evolution

The ARMH1 gene is extremely diverse and is found in thousands of different species. From primates to fungus, this gene has been evolutionarily relevant for hundreds of millions of years. While in near relatives such as cows, the similarity score is 91% that of our genome, in species of fungi the similarity ranges between 20 and 30%. While attempting to find homologs in any round or flat worms, single celled eukaryotes or prokaryotes, plants, or any fungi besides chitrids, there were no significantly similar genes found. Below is a table of orthologous genes in order of sequence similarity compared to the human ARMH1 isoform X1.

Clinical significance

The ARMH1 gene and subsequent protein have been extensively linked to leukemia, specifically T-cell acute lymphoblastic leukemia (T-ALL). In mostly lymphatic tissue cell lines, T-ALL showed dramatically increased expression of the ARMH1 gene. Bone marrow samples were taken at the initial diagnosis and the conclusion of treatment and ARMH1 along with 5 other genes that were all found to be dramatically changed in expression. To corroborate these findings, once again ARMH1 saw a 1.8x expression increase in samples after diagnosis of leukemia. Higher ARMH1 expression was significantly associated with poor overall survival.

References

1. List of human protein-coding genes 1
2. Armillaria mellea