The ARD1 (disrupt defective 1, ARD1) gene is a member of the N-acetyltransferase (NAT) family. ARD1 is an acetyltransferase. Silva et al. clarify that ARD1 functions mainly by regulating protein-protein interactions, protein stability, protein function, and protein localization to specific organelles. ARD1 was originally discovered in yeast, and yeast ARD1 is one of the three subunits that make up the N2 acetyltransferase NatA (NAT1, ARD1, NAT5). Park et al. found that ARD1 mainly functions as an N-α-acetyltransferase, which can transfer the acetyl group (-CO-CH3) of acetyl-CoA to the N-terminus of the nascent polypeptide, thereby affecting the function and stability of the protein. At the same time, it also plays an important role in the regulation of the cell cycle.
There are two activities in ARD1 in mammals: the ε-amino group of the lysine residue and the α-amino acetylation activity at the N-terminus. The acetylation mediated by ARD1 is ubiquitous in the protein components of various tissues of eukaryotic cells. It plays a role in post-translational modification in many biological processes, such as DNA repair, protein stability and nuclear translocation, interactions between proteins, cell proliferation, apoptosis, autophagy and neural development. In addition, it plays a vital role in the development of tumors. ARD1 is widely expressed in various tissues of the human body, including brain, heart, liver, skeletal muscle, intestine, spleen, kidney, etc. At the cellular level, it is mainly expressed in the cytoplasm and only slightly expressed in the nucleus. Ma et al. found that human N-acetyltransferase ARD1 is highly correlated with tumors such as lung cancer, breast cancer, colorectal cancer, prostate cancer, thyroid cancer, etc., and is highly expressed in many tumor tissues and cells.
ARD1 and Cell Proliferation
Cell proliferation is one of the important physiological functions of living cells. It is an important life feature of organisms by proliferating in a split manner. The timing of the cell cycle is tightly regulated by different genes. As an acetyltransferase, ARD1 plays an important regulatory role in cell growth and differentiation. However, there are few reports on the regulation of related enzymes and biological activities in the process of ARD1 regulating tumor cell proliferation. The specific mechanism has not yet formed a unified consensus. Park et al found that S period ARD1 was highly expressed in the nucleus of proliferating cells, and nuclear localization signal (NLS) knockout prevented ARD1 from entering the nucleus, leading to cell morphological changes and cell growth disorders. Once the exogenous NLS activates ARD1, the cells gradually return to normal morphology.
Figure 1. Isoform-specific roles of ARD1 autoacetylation in tumorigenesis. (Seo, et al. 2014).
Foyn et al., based on NAT-specific substrates, synthesized three class of substrate analogs CoA-Ac-SES4, CoA-Ac-EEE4, and CoA-Ac-MLG7 as selective inhibitors. Studies have shown that ARD1 (hnaa10) can inhibit the proliferation of cancer cells and cause cell death, and can also increase the drug-induced cytotoxicity of cancer cells. Seo et al. injected ARD1, which was artificially spliced with different functional fragment mRNAs, into mice, studied their cellular activities and isolated and sequenced ARD1 from HeLa cells. Sequence alignment revealed that ARD1 variants were less common than mouse ard1 (mard1), and the most common form of ARD1, ARD1 (131), had an altered reading frame encoding a 46 bp deletion gene sequence. ARD1 (235) stimulates cell proliferation by up-regulating cyclin D1, whereas ARD1 (131) does not affect cyclin D1 expression or cell growth. In addition, ARD1 (131) and ARD1 (235) subcellular localization are also different. ARD1 (131) is mainly distributed in the nucleus, while ARD1 (235) is mainly located in the cytosol. Animal experiments by Seo et al also showed that mard1 (225) can inhibit tumor angiogenesis under hypoxia and reduce the stability of hypoxia-inducible factor α (HIF-1α).
ARD1 and Apoptosis
Cell apoptosis is a physiological pathological stimulus signal of the cell to the environment, and a death process in which changes in environmental conditions or gradual damage occur in response to orderly changes. The occurrence of tumors is not only the result of excessive cell proliferation but also has a great relationship with the obstruction of the apoptotic pathway. Park et al. confirmed by experiments that ARD1 can regulate the apoptosis of colorectal cancer cells, and also the mechanism of ARD1 regulation of apoptosis. Park believes that ARD1 binds to receptor-associated protein 1 and thus regulates the activity of doxorubicin-induced NF-kB subunit RelA/p65 acetylation, further regulating the activity of the anti-apoptotic protein MCL1, thereby inhibiting the apoptosis of knot cancer cell.
In the caspase pathway induced by daunorubicin (DNR), ARD1 and NATH were cleaved, resulting in a 40% to 80% reduction in NATs activity. Some studies have used RNA interference technology to inhibit the expression of ARD1 in Hep-G2 cell line. It is confirmed that ARD1 silencing induces apoptosis by gene chip technology, and found that ARD1 silencing leads to a trend of gene change similar to that of under hypoxic conditions. The study found that in the process of colorectal cancer tumor formation, the activity of wild-type p53 is regulated by various acetyltransferases and deacetylases to achieve anti-apoptotic ability. ARD1 may play an important role in the regulation of promoter and transcriptional activity by p53.
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