GO:0140229 histone isonicotinyllysine deisonicotinylase activity

Histone isonicotinyllysine deisonicotinylase activity (GO:0140229) is a molecular function that catalyzes the hydrolysis of N6-isonicotinyl-L-lysine on proteins, specifically histones, to release isonicotinate and regenerate unmodified lysine. This activity was discovered in the context of isoniazid, a first-line anti-tuberculosis drug that induces isonicotinylation as a novel histone mark. The identification of this modification and its removal has opened a new area of research into how drugs can directly alter the epigenome and how cells reverse such modifications. For researchers, GO:0140229 represents a critical enzymatic activity that may regulate gene expression programs by erasing a drug-induced histone mark. The existence of a deisonicotinylase implies a dynamic and reversible process, similar to other histone acylation marks, and suggests that specific enzymes evolved to remove isonicotinyl groups. Understanding this activity is essential for interpreting the epigenetic effects of isoniazid and potentially other hydrazide-containing compounds. Moreover, global isonicotinylome studies have revealed that isonicotinylation can target non-histone proteins such as SMAD3, where it promotes epithelial-mesenchymal transition and invasion in liver cancer cells. This broadens the relevance of deisonicotinylase activity beyond histones and highlights its potential impact on cancer biology and drug response. Thus, GO:0140229 is a focal point for connecting drug metabolism, epigenetic regulation, and disease mechanisms [1,2].

GO:0140229, histone isonicotinyllysine deisonicotinylase activity, is defined as the catalysis of the reaction: N(6)-isonicotinyl-L-lysyl-[protein] + H2O = isonicotinate + L-lysyl-[protein]. In simpler terms, it is an enzyme activity that removes an isonicotinyl group from a modified lysine residue on a histone protein, using water to cleave the bond and releasing isonicotinate. This activity reverses the histone mark known as isonicotinylation, which is induced by isoniazid.

GO:0140229 is important because it represents a reversible enzymatic activity that controls a drug-induced histone modification, thereby linking xenobiotic metabolism to epigenetic regulation. The discovery of isonicotinylation as a histone mark and the existence of a deisonicotinylase suggest that cells can actively remove isoniazid-derived modifications, which may influence gene expression and drug responses. Furthermore, isonicotinylation of non-histone proteins like SMAD3 has been implicated in cancer progression, making deisonicotinylase activity a potential modulator of disease pathways. Understanding this activity could lead to new insights into tuberculosis treatment side effects, cancer biology, and the broader field of histone eraser enzymes [1,2].

The following genes and proteins are implicated in isonicotinylation, deisonicotinylase activity, or related regulatory pathways based on published literature [1,2].

The regulation of histone isonicotinyllysine deisonicotinylase activity is not yet well defined, but it is likely controlled by the availability of the isonicotinylated substrate and the expression or activity of the responsible enzyme(s). Since isonicotinylation is induced by isoniazid, the activity may be upregulated as a response to drug exposure to reverse the modification. Additionally, cellular metabolic states that affect cofactors such as NAD+ could influence the activity if the enzyme belongs to the sirtuin family. However, direct evidence for specific regulatory mechanisms is currently lacking and requires further investigation.

Isonicotinylation of SMAD3 has been shown to promote epithelial-mesenchymal transition and invasion in liver cancer cells. This suggests that deisonicotinylase activity, by removing the isonicotinyl group from SMAD3, could potentially reverse these pro-metastatic effects. However, the specific role of histone deisonicotinylase activity in liver cancer remains to be directly investigated.

Isoniazid, a first-line anti-tuberculosis drug, induces histone isonicotinylation, which may contribute to side effects or altered gene expression during treatment. The existence of a deisonicotinylase suggests that cells attempt to remove this modification, and individual differences in this activity could influence drug response or toxicity. Understanding this process may lead to strategies to mitigate isoniazid-induced epigenetic changes.

Histone isonicotinylation represents a novel epigenetic mark that can alter chromatin structure and gene expression. The deisonicotinylase activity that removes this mark is therefore a key regulator of epigenetic plasticity. Dysregulation of this activity could contribute to diseases characterized by aberrant gene expression, though direct evidence is currently limited.

Mass spectrometry-based proteomics can identify proteins modified by isonicotinylation, including histones and non-histone proteins like SMAD3. This method involves enriching isonicotinylated peptides using specific antibodies or chemical probes, followed by LC-MS/MS analysis. It provides a global view of the isonicotinylome and can reveal target sites for deisonicotinylase activity.

Western blotting with anti-isonicotinyl antibodies can detect changes in histone isonicotinylation levels after manipulating candidate deisonicotinylases. Immunoprecipitation of specific histones followed by immunoblotting can confirm the modification status of individual proteins. These methods are useful for validating findings from high-throughput screens.

In vitro assays using synthetic isonicotinylated histone peptides can measure the release of isonicotinate or the formation of unmodified lysine. These assays can be coupled with mass spectrometry or fluorescence to quantify activity. They are essential for characterizing the kinetic properties and substrate specificity of candidate enzymes.

Genome-wide CRISPR knockout or activation screens can be used to identify genes that regulate histone isonicotinylation levels. Cells are treated with isoniazid, and isonicotinyl marks are detected by immunofluorescence or flow cytometry to isolate modulators. This approach can uncover novel eraser enzymes, including deisonicotinylases.

Researchers studying histone isonicotinyllysine deisonicotinylase activity-related genes often need to determine whether a candidate gene is causally involved in removing the isonicotinyl mark, how mutations affect enzyme function, and what downstream pathways are impacted. EDITGENE provides a comprehensive suite of CRISPR-based services to address these questions with precision and reproducibility.

Histone isonicotinyllysine deisonicotinylase activity (GO:0140229) represents a newly discovered enzymatic function that reverses a drug-induced histone modification. Its study bridges epigenetics, drug metabolism, and disease biology, with implications for tuberculosis treatment and cancer progression [1,2]. Continued research using CRISPR models and advanced proteomics will likely identify the responsible enzymes and uncover their regulatory roles.