The many faces of lysine acylation in proteins: Phytohormones as unexplored substrates

Protein post-translational modification (PTM) is a ubiquitous process that occurs in most proteins. Lysine residues containing an ε-amino group are recognized as hotspots for the addition of different chemical groups. Lysine acetylation, extensively studied in histones, serves as an epigenetic hallmark capable of promoting changes in chromatin structure and availability. Acyl groups derived from molecules involved in carbohydrate and lipid metabolisms, such as lactate, succinate and hydroxybutyrate, were identified as lysine modifications of histones and other proteins. Lysine-acyltransferases do not exhibit significant substrate specificity concerning acyl donors. Furthermore, plant hormones harboring acyl groups often form conjugates with free amino acids to regulate their activity and function during plant physiological processes and responses, a process mediated by GH3 enzymes. Besides forming low-molecular weight conjugates, auxins have been shown to covalently modify proteins in bean seeds. Aside from auxins, other phytohormones with acyl groups are unexplored potential substrates for post-translational acylation of proteins. Using MS data searches, we revealed various proteins with lysine residues linked to auxin, abscisic acid, gibberellic acid, jasmonic acid, and salicylic acid. These findings raise compelling questions about the ability of plant hormones harboring carboxyl groups to serve as new candidates for protein acylation and acting in protein PTM and modulation.

Analysis of Golgi Protein Acetylation Using In Vitro Assays and Parallel Reaction Monitoring Mass Spectrometry

Acetylation is one of the most abundant post-translational protein modifications that regulates all cellular compartments ranging from chromatin to cytoskeleton and Golgi. The dynamic acetylation of the Golgi stacking protein GRASP55 was shown to regulate Golgi reassembly after mitosis. Here we provide a detailed protocol for the analysis of Golgi acetylation including in vitro assays to detect protein acetylation and mass spectrometry analysis to identify specific acetylation sites and their relative abundance.

Sulforaphane and iberin are potent epigenetic modulators of histone acetylation and methylation in malignant melanoma

OBJECTIVE(S)

Growing evidence supports that isothiocyanates exert a wide range of bioactivities amongst of which is their capacity to interact with the epigenetic machinery in various cancers including melanoma. Our aim was to characterise the effect of sulforaphane and iberin on histone acetylation and methylation as a potential anti-melanoma strategy.

METHODS

We have utilised an in vitro model of malignant melanoma [consisting of human (A375, Hs294T, VMM1) and murine (B16F-10) melanoma cell lines as well as a non-melanoma (A431) and a non-tumorigenic immortalised keratinocyte (HaCaT) cell line] exposed to sulforaphane or iberin. Cell viability was evaluated by the Alamar blue assay whilst total histone deacetylases and acetyltransferases activities were determined by the Epigenase HDAC Activity/Inhibition and EpiQuik HAT Activity/Inhibition assay kits, respectively. The expression levels of specific histone deacetylases and acetyltransferases together with those of lysine acetylation and methylation marks were obtained by western immunoblotting.

RESULTS

Overall, both sulforaphane and iberin were able to (1) reduce cell viability, (2) decrease total histone deacetylase activity and (3) modulate the expression levels of various histone deacetylases as well as acetyl and methyl transferases thus modulating the acetylation and methylation status of specific lysine residues on histones 3 and 4 in malignant melanoma cells.

CONCLUSIONS

Our findings highlight novel insights as to how sulforaphane and iberin differentially regulate the epigenetic response in ways compatible with their anticancer action in malignant melanoma.

Allyl isothiocyanate regulates lysine acetylation and methylation marks in an experimental model of malignant melanoma

Objective(s)

Isothiocyanates (ITCs) are biologically active plant secondary metabolites capable of mediating various biological effects including modulation of the epigenome. Our aim was to characterize the effect of allyl isothiocyanate (AITC) on lysine acetylation and methylation marks as a potential epigenetic-induced anti-melanoma strategy.

Methods

Our malignant melanoma model consisted of (1) human (A375) and murine (B16-F10) malignant melanoma as well as of human; (2) brain (VMM1) and lymph node (Hs 294T) metastatic melanoma; (3) non-melanoma epidermoid carcinoma (A431) and (4) immortalized keratinocyte (HaCaT) cells subjected to AITC. Cell viability, histone deacetylases (HDACs) and acetyltransferases (HATs) activities were evaluated by the Alamar blue, Epigenase HDAC Activity/Inhibition and EpiQuik HAT Activity/Inhibition assay kits, respectively, while their expression levels together with those of lysine acetylation and methylation marks by western immunoblotting. Finally, apoptotic gene expression was assessed by an RT-PCR-based gene expression profiling methodology.

Results

AITC reduces cell viability, decreases HDACs and HATs activities and causes changes in protein expression levels of various HDACs, HATs, and histone methyl transferases (HMTs) all of which have a profound effect on specific lysine acetylation and methylation marks. Moreover, AITC regulates the expression of a number of genes participating in various apoptotic cascades thus indicating its involvement in apoptotic induction.

Conclusions

AITC exerts a potent epigenetic effect suggesting its potential involvement as a promising epigenetic-induced bioactive for the treatment of malignant melanoma.