Protein Kinase C Theta Modulates PCMT1 through hnRNPL to Regulate FOXP3 Stability in Regulatory T Cells

Abstract

T cell receptor signaling, together with cytokine-induced signals, can differentially regulate RNA processing to influence T helper versus regulatory T cell fate. Protein kinase C family members have been shown to function in alternative splicing and RNA processing in various cell types. T cell-specific protein kinase C theta, a molecular regulator of T cell receptor downstream signaling, has been shown to phosphorylate splicing factors and affect post-transcriptional control of T cell gene expression. In this study, we explored how using a synthetic cell-penetrating peptide mimic for intracellular anti-protein kinase C theta delivery fine-tunes differentiation of induced regulatory T cells through its differential effects on RNA processing. We identified protein kinase C theta signaling as a critical modulator of two key RNA regulatory factors, heterogeneous nuclear ribonucleoprotein L (hnRNPL) and protein-Lisoaspartate O-methyltransferase-1 (PCMT1), and loss of protein kinase C theta function initiated a "switch" in post-transcriptional organization in induced regulatory T cells. More interestingly, we discovered that protein-L-isoaspartate Omethyltransferase-1 acts as an instability factor in induced regulatory T cells, by methylating the forkhead box P3 (FOXP3) promoter. Targeting protein-L-isoaspartate O-methyltransferase-1 using a cell-penetrating antibody revealed an efficient means of modulating RNA processing to confer a stable regulatory T cell phenotype.

Recent insights into the role of Akt in CD4 T-cell activation and differentiation: alternative splicing and beyond

“…Our own studies identified RNA processing factors, including hnRNP A1 and hnRNP L, as Akt targets during T H cell differentiation [15] . A recent study examined the role of AS and RNA processing in Treg induction and stability [49] . This study showed that inhibition of PKCθ during in vitro Treg differentiation altered AS patterns by affecting the activity of the RNA processing factor hnRNP L and the methyltransferase PCMT1, leading to greater stability of Treg [49] .…”

“…A recent study examined the role of AS and RNA processing in Treg induction and stability [49] . This study showed that inhibition of PKCθ during in vitro Treg differentiation altered AS patterns by affecting the activity of the RNA processing factor hnRNP L and the methyltransferase PCMT1, leading to greater stability of Treg [49] . While this study did not directly examine the role of Akt, the authors proposed that it could be playing a role in controlling PCMT1 function, and further studies are needed to confirm this speculation.…”

“…Sequencing of the human genome and transcriptome has revealed that over 90% of multi-exon genes are alternatively spliced in a tissue-specific manner [45,46] . AS is regulated by RNA-binding protein (RBP) activity [47,48] , many RBPs are known to control AS in immune cells [47,48] , and there is increasing evidence that Akt controls the function of these proteins [15,49] .…”

PCMT1 Is a Potential Prognostic Biomarker and Is Correlated with Immune Infiltrates in Breast Cancer

“…The main functions of PCMT1 are to initiate the repair of damaged proteins by catalyzing methyl esterification of L-isoaspartyl and D-aspartyl residues produced by spontaneous isomerization and racemization of L-aspartyl and L-asparaginyl residues in aging peptides and proteins. Previous studies have shown that strong PCMT1 expression is not only a predictive marker for poor prognosis of surgically removed lung adenocarcinoma but also an unfavorable prognostic biomarker for bladder cancer [ 12 – 14 ]. It participates in cell migration and invasion by regulating epithelial-mesenchymal transition-related genes and acts as an oncogene in bladder cancer [ 15 ].…”

Increased block copolymer length improves intracellular availability of protein cargo

“…39,42 Additionally, PTDMs constructed from a hydrophobic monomer featuring methyl and phenyl substituents (MePh) and a cationic monomer containing two guanidine groups (dG) have demonstrated robust delivery of several functional proteins, including antibodies and enzymes. 29,[42][43][44][45][46] Maintaining a 2 : 1 ratio of MePh to dG, five carriers were synthesized with DPs of 15-120 (6-46 kDa in size). This series of block copolymers was used here to deliver EGFP, IgG, and Cre recombinase to elucidate the impact of molecular weight on both internalization and protein activity.…”