DQ 65–79, A Peptide Derived from HLA Class II, Mimics p21 to Block T Cell Proliferation

Targeting Proliferating Cell Nuclear Antigen (PCNA) as an Effective Strategy to Inhibit Tumor Cell Proliferation

Targeting highly proliferating cells is an important issue for many types of aggressive tumors. Proliferating Cell Nuclear Antigen (PCNA) is an essential protein that participates in a variety of processes of DNA metabolism, including DNA replication and repair, chromatin organization and transcription and sister chromatid cohesion. In addition, PCNA is involved in cell survival, and possibly in pathways of energy metabolism, such as glycolysis. Thus, the possibility of targeting this protein for chemotherapy against highly proliferating malignancies is under active investigation. Currently, approaches to treat cells with agents targeting PCNA rely on the use of small molecules or on peptides that either bind to PCNA, or act as a competitor of interacting partners. Here, we describe the status of the art in the development of agents targeting PCNA and discuss their application in different types of tumor cell lines and in animal model systems.

Polymer Cancerostatics Containing Cell-Penetrating Peptides: Internalization Efficacy Depends on Peptide Type and Spacer Length

Cell-penetrating peptides (CPPs) are commonly used substances enhancing the cellular uptake of various cargoes that do not easily cross the cellular membrane. CPPs can be either covalently bound directly to the cargo or they can be attached to a transporting system such as a polymer carrier together with the cargo. In this work, several CPP-polymer conjugates based on copolymers of N-(2-hydroxypropyl)methacrylamide (pHPMA) with HIV-1 Tat peptide (TAT), a minimal sequence of penetratin (PEN), IRS-tag (RYIRS), and PTD4 peptide, and the two short hydrophobic peptides VPMLK and PFVYLI were prepared and characterized. Moreover, the biological efficacy of fluorescently labeled polymer carriers decorated with various CPPs was compared. The experiments revealed that the TAT-polymer conjugate and the PEN-polymer conjugate were internalized about 40 times and 15 times more efficiently than the control polymer, respectively. Incorporation of dodeca(ethylene glycol) spacer improved the cell penetration of both studied polymer-peptide conjugates compared to the corresponding spacer-free polymer conjugates, while the shorter tetra(ethylene glycol) spacer improved only the penetration of the TAT conjugate but it did not improve the penetration of the PEN conjugate. Finally, a significantly improved cytotoxic effect of the polymer conjugate containing anticancer drug pirarubicin and TAT attached via a dodeca(ethylene glycol) was observed when compared with the analogous polymer-pirarubicin conjugate without TAT.

Cell-Penetrating Peptides: a Useful Tool for the Delivery of Various Cargoes Into Cells

Cell-penetrating compounds are substances that enhance the cellular uptake of various molecular cargoes that do not easily cross the cellular membrane. The majority of cell-penetrating compounds described in the literature are cell-penetrating peptides (CPPs). This review summarizes the various structural types of cell-penetrating compounds, with the main focus on CPPs. The authors present a brief overview of the history of CPPs, discuss the various types of conjugation of CPPs to biologically active cargoes intended for cell internalization, examine the cell-entry mechanisms of CPPs, and report on the applications of CPPs in research and in preclinical and clinical studies.

The latest developments in synthetic peptides with immunoregulatory activities

In the past few years, many researches have provided us with much data demonstrating the abilities of synthetic peptides to impact immune response in vitro and in vivo. These peptides were designed according to the structure of some important protein molecules which play a key role in immune response, so they act with specific targets. The class I and II MHC-derived peptides inhibit the TCR recognition of antigen peptide-MHC complex. Rationally designed CD80 and CD154-binding peptides block the interaction between cell surface costimulatory molecules on antigen-presenting cells (APCs) and T cells. Some peptides were designed to inhibit the activities of cell signal proteins, including JNK, NF-κB and NFAT. Some peptide antagonists competitively bind to important cytokines and inhibit their activities, such as TNF-α, TGF-β and IL-1β inhibitory peptides. Adhesion molecule ICAM-1 derived peptides block the T cell adhesion and activation. These immunoregulatory peptides showed therapeutic effect in several animal models, including collagen-induced arthritis (CIA), autoimmune cystitis model, murine skin transplant model and cardiac allograft model. These results give us important implications for the development of a novel therapy for immune mediated diseases.

Proliferating cell nuclear antigen acts as a cytoplasmic platform controlling human neutrophil survival

Cytosolic proliferating cell nuclear antigen (PCNA) binds to procaspases and protects human neutrophils from apoptosis.

Neutrophil apoptosis is a highly regulated process essential for inflammation resolution, the molecular mechanisms of which are only partially elucidated. In this study, we describe a survival pathway controlled by proliferating cell nuclear antigen (PCNA), a nuclear factor involved in DNA replication and repairing of proliferating cells. We show that mature neutrophils, despite their inability to proliferate, express high levels of PCNA exclusively in their cytosol and constitutively associated with procaspases, presumably to prevent their activation. Notably, cytosolic PCNA abundance decreased during apoptosis, and increased during in vitro and in vivo exposure to the survival factor granulocyte colony-stimulating factor (G-CSF). Peptides derived from the cyclin-dependent kinase inhibitor p21, which compete with procaspases to bind PCNA, triggered neutrophil apoptosis thus demonstrating that specific modification of PCNA protein interactions affects neutrophil survival. Furthermore, PCNA overexpression rendered neutrophil-differentiated PLB985 myeloid cells significantly more resistant to TNF-related apoptosis-inducing ligand– or gliotoxin-induced apoptosis. Conversely, a decrease in PCNA expression after PCNA small interfering RNA transfection sensitized these cells to apoptosis. Finally, a mutation in the PCNA interdomain-connecting loop, the binding site for many partners, significantly decreased the PCNA-mediated antiapoptotic effect. These results identify PCNA as a regulator of neutrophil lifespan, thereby highlighting a novel target to potentially modulate pathological inflammation.

DQA1*03011 allele: protective or an adverse effect on the development of sarcoidosis; preliminary study

BACKGROUND

Sarcoidosis (SA) is a multisystem granulomatous disorder of unknown etiology. It seems likely that in genetically different predisposed hosts, the same antigen(s) may cause the development of sarcoid Th1 response. The interaction of the T-cell receptor with the human leukocyte antigen-DQA1*03011 peptide-complex can affect T lymphocytes activation in a dose-response manner.

OBJECTIVES/METHODS

To test occurrence of DQA1*03011 allele in SA, we compared the distribution of DQA1 alleles in 32 SA patients, 37 TB patients and in 58 healthy volunteers, using a PCR-SSP "high-resolution" method.

RESULTS

Our results revealed that after Bonferroni correction DQA1*03011 were less common in SA patients than in the controls (OR 0.16, 95%CI 0.03-0.75). In TB, DQA1*0303 were significantly more frequent and DQA1*0505 less present as compared to the controls (OR 11.03, 95% CI 1.20-95.80, OR 0.29, 95% CI 0.01-0.88). Comparing DQA1 alleles in both patient groups, DQA1*0501, DQA1*0505 alleles were more common and DQA1*03011, DQA1*0302, DQA1*0303 were less common after Bonferroni correction in SA than in TB.

CONCLUSION

We revealed that DQA1*03011 allele was less common in SA than in the controls and TB. It seems possible that a low frequency of DQA1*03011 occurrence may be also involved in the etiopathogenesis of SA.

Peptide-mediated immunosuppression

There is now a substantial body of data demonstrating the abilities of synthetic peptides and peptide analogues to inhibit the auto- and alloimmune response in vitro and in vivo. We have studied the immunomodulatory role of synthetic peptides derived from highly conserved regions of the class II MHC alpha chain. These MHC-derived peptides inhibit the rat, human, and mouse mixed lymphocyte response (MLR), proliferation to autoantigen, cytokine production, and cytolytic T lymphocyte (CTL) generation. Our studies demonstrated that the inhibitory effect of the MHC class II nonpolymorphic peptides is mediated through the induction of apoptosis in APCs via a nonclassic caspase-independent pathway. In addition, T lymphocytes initially stimulated in the presence of HLA-DQA1 are rendered hyporesponsive to subsequent stimuli. Immunomodulation by HLA-DQA1 was effective in vivo because it prevented both the priming and the effector function of primed allogeneic T cells in a murine DTH model. Our data demonstrate that peptides derived from highly conserved regions of the class II MHC alpha chain can alter T-lymphocyte immune responses both in vitro and in vivo. These results have important implications for the development of a novel therapy for immune mediated diseases.

MHC Class II–Mediated Apoptosis by a Nonpolymorphic MHC Class II Peptide Proceeds by Activation of Protein Kinase C

It was demonstrated previously that a peptide derived from a conserved region of MHC class II, HLA-DQA1, inhibits proliferation of allogeneic T cells in vitro. Administration of HLA-DQA1 in conjunction with allogeneic cells at the time of priming or at the time of rechallenge prevented the development of the delayed type hypersensitivity response in vivo. The immunomodulatory effects of HLA-DQA1 were associated with the induction of apoptosis in B cells, macrophages, and dendritic cells via a caspase-independent pathway. This study investigated the binding site and mechanism that mediates cell death induced by HLA-DQA1. It was demonstrated that HLA-DQA1 binds to MHC class II on the cell surface, causing MHC class II signaling, initiation of protein kinase C signaling, and mitochondrial membrane depolarization with resultant apoptosis. The data indicate that HLA-DQA1 binds to MHC class II outside the groove, in a manner similar to superantigen. These results suggest that HLA-DQA1 is a novel immunotherapy that may provide an effective means of targeting professional antigen-presenting cells, in particular B cells.

A novel apoptosis pathway activated by the carboxyl terminus of p21

Delivery of biologically active peptides into cells may help elucidate intracellular signal transduction pathways, identify additional in vivo functions, and develop new therapeutics. Although p21 was first identified as a major regulator of cell cycle progression, it is now clear that p21 subserves multiple functions. The amino terminus of p21 interacts with cyclins and cyclin-dependent kinases, while the carboxyl terminus interacts with proliferating cell nuclear antigen (PCNA), growth arrest and DNA damage-inducible gene 45 (GADD45), calmodulin, SET, and CCAAT/enhancer binding protein-alpha (C/EBP-alpha). A chimeric peptide, p21-IRS, consisting of the carboxyl terminal domain of p21 conjugated to a pentapeptide (RYIRS) rapidly enters lymphoid cells and activates apoptosis. In the present study, we investigate the molecular events involved in p21-activated apoptosis. Comparison of p21-IRS with other known proapoptotic agents demonstrates that p21-IRS activates a novel apoptotic pathway: mitochondria are central to the process, but caspases and a decrease in Deltapsi(m) are not involved. Targeting the p21 peptide to specific cell populations may allow development of novel therapies to eliminate aberrant cells in human diseases.