A Novel Role of PP2A Methylation in the Regulation of Tight Junction Assembly and Integrity

Mechanisms and rationales of SAM homeostasis

S-Adenosylmethionine (SAM) is the primary methyl donor for numerous cellular methylation reactions. Its central role in methylation and involvement with many pathways link its availability to the regulation of cellular processes, the dysregulation of which can contribute to disease states, such as cancer or neurodegeneration. Emerging evidence indicates that intracellular SAM levels are maintained within an optimal range by a variety of homeostatic mechanisms. This suggests that the need to maintain SAM homeostasis represents a significant evolutionary pressure across all kingdoms of life. Here, we review how SAM controls cellular functions at the molecular level and discuss strategies to maintain SAM homeostasis. We propose that SAM exerts a broad and underappreciated influence in cellular regulation that remains to be fully elucidated.

Impact of peptide permeation enhancer on tight junctions opening cellular mechanisms

The myristoylated pentapeptide, L-R5, contains an amino acid sequence of the zeta inhibitory peptide (ZIP) portion (pseudosubstrate) of protein kinase C zeta (PKC ζ). As PKC ζ is involved in the modulation of epithelial tight junctions (TJs) through the phosphorylation of TJ proteins, L-R5 was suggested to interact with the enzyme resulting in the enhancement of paracellular permeability. This study shows that L-R5 does not bind to the enzyme but interacts directly with TJ proteins. We show here that the binding of PKC ζ to occludin and its successive phosphorylation is prevented by L-R5, which leads to TJ disruption and enhanced epithelial permeability. Although L-R5 did not show any in vitro cytotoxicity, a proteomics study revealed that L-R5 interferes with other regulatory pathways, e.g., apoptosis and immune response. We suggest that structural modification of the peptide may increase the specificity TJ protein-peptide interaction.

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Microscale thermophoresis (MST) showed robust results for protein bindings.

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The competitivity of L-R5 peptide for the binding of occludin-PKC zeta was shown.

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Tight junctions proteins expression was decreased due to L-R5 peptide.

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Multiple other mechanisms can be explored to use L-R5 for other therapies.