Components of the heterogeneous nuclear ribonucleoprotein (hnRNP) complex and other nucleic acid-binding proteins are subject to methylation on specific arginine residues by the catalytic activity of arginine methyltransferases. The methylation has been implicated in transcriptional regulation and RNA and protein trafficking and signal transduction, but the mechanism by which these functions are achieved has remained undetermined. We show here that the predominant arginine methyltransferase in human cells, protein arginine methyltransferase 1 (PRMT1), is associated with hnRNP complexes, dependent on the methylation status of the cell, and that it methylates its preferred substrates in situ. Binding of PRMT1 occurs through physical interaction with scaffold attachment factor A (SAF-A), also known as hnRNP-U, which is quantitatively methylated by PRMT1 in all investigated cell lines as determined by a novel, highly specific, methylation-sensitive antibody.

Current therapies for autoimmune chronic inflammatory diseases e.g. rheumatoid arthritis (RA) include inhibitors of inflammatory cytokines. However, these therapies can result in increased risk of infections. There is a need to explore alternate strategies that can control inflammation without compromising the innate ability to resolve infections. In this study, we examined the effect of small peptides derived from endogenous cathelicidin peptides in a murine model of collagen-induced arthritis (CIA). Cathelicidins are immunomodulatory peptides known to control infections. We demonstrate that the administration of the peptide IG-19, which represents an internal segment of the human cathelicidin LL-37, decreased disease severity and significantly reduced the serum levels of antibodies against collagen type II in the CIA model. IG-19 peptide reduced cellular infiltration in joints, prevented cartilage degradation and suppressed pro-inflammatory cytokines in the CIA mice. We also showed that not all cathelicidin-derived peptides exhibit similar functions. A bovine cathelicidin-derived peptide IDR-1018 did not exhibit the beneficial effects observed with the human cathelicidin LL-37-derived peptide IG-19, in the same murine model of CIA. This is the first study to provide evidence demonstrating the ability of a peptide derived from the human cathelicidin LL-37 to alleviate the arthritic disease process in a murine model of RA. Our results has lead us to propose a new approach for controlling autoimmune chronic inflammatory disorders such as RA, by using specific synthetic derivatives of endogenous host defence peptides. Cathelicidin-derived peptides are particularly attractive for their dual antimicrobial and anti-inflammatory actions.

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During virion morphogenesis herpes simplex virus nucleocapsids transit from the nucleoplasm to the cytoplasm, through a process called nuclear egress, where the final stages of virion assembly occur. Coupled to nuclear egress is a poorly understood quality-control mechanism that preferentially selects genome-containing C-capsids, rather than A- and B-capsids that lack genomes, for transit to the cytoplasm. We and others have reported that cells infected with HSV strains deleted for the tegument protein pUL21 accumulate both empty A-capsids and C-capsids in the cytoplasm of infected cells. Quantitative microscopy experiments indicated that C-capsids were preferentially selected for envelopment at the inner nuclear membrane and that nuclear integrity remained intact in cells infected with pUL21 mutants, prompting alternative explanations for the accumulation of A-capsids in the cytoplasm. More A-capsids were also found in the nuclei of cells infected with pUL21 mutants compared to their wild type (WT) counterparts, suggesting pUL21 might be required for optimal genome packaging or genome retention within capsids. In support of this, more viral genomes were prematurely released into the cytoplasm during pUL21 mutant infection compared to WT infection and led to enhanced activation of cellular cytoplasmic DNA sensors. Mass spectrometry and western blot analysis of WT and pUL21 mutant capsids revealed an increased association of the known pUL21 binding protein, pUL16, with pUL21 mutant capsids, suggesting that premature and/or enhanced association of pUL16 with capsids might result in capsid destabilization. Further supporting this idea, deletion of pUL16 from a pUL21 mutant strain rescued genome retention within capsids. Taken together, these findings suggest that pUL21 regulates pUL16 addition to nuclear capsids and that premature, and/or, over-addition of pUL16 impairs HSV genome retention within capsids.

During virion morphogenesis herpes simplex virus nucleocapsids transit from the nucleoplasm to the cytoplasm, through a process called nuclear egress, where the final stages of virion assembly occur. Coupled to nuclear egress is a poorly understood quality-control mechanism that preferentially selects genome-containing C-capsids, rather than A- and B-capsids that lack genomes, for transit to the cytoplasm. Cells infected with HSV strains deleted for the tegument protein pUL21 accumulate both empty A-capsids and C-capsids in the cytoplasm of infected cells. Quantitative microscopy experiments indicated that C-capsids were preferentially selected for envelopment at the inner nuclear membrane and that nuclear integrity remained intact in cells infected with pUL21 mutants, prompting alternative explanations for the accumulation of A-capsids in the cytoplasm. More A-capsids were also found in the nuclei of cells infected with pUL21 mutants suggesting pUL21 might be required for optimal genome packaging or genome retention within capsids. In support of this, viral genomes were prematurely released into the cytoplasm during pUL21 mutant infection that led to enhanced activation of cellular cytoplasmic DNA sensors. Analysis of WT and pUL21 mutant capsids revealed an increased association of the known pUL21 binding protein, pUL16, with pUL21 mutant capsids, suggesting that premature and/or enhanced association of pUL16 with capsids might result in capsid destabilization. Further supporting this idea, deletion of pUL16 from a pUL21 mutant strain rescued genome retention within capsids. These findings suggest that pUL21 regulates pUL16 addition to nuclear capsids and that premature, and/or, over-addition of pUL16 impairs HSV genome retention within capsids.