NKp44-Derived Peptide Binds Proliferating Cell Nuclear Antigen and Mediates Tumor Cell Death

Abstract

Proliferating cell nuclear antigen (PCNA) is considered as a hub protein and is a key regulator of DNA replication, repair, cell cycle control, and apoptosis. PCNA is overexpressed in many cancer types, and PCNA overexpression is correlated with cancer virulence. Membrane-associated PCNA is a ligand for the NKp44 (NCR2) innate immune receptor. The purpose of this study was to characterize the PCNA-binding site within NKp44. We have identified NKp44-derived linear peptide (pep8), which can specifically interact with PCNA and partly block the NKp44–PCNA interaction. We then tested whether NKp44-derived pep8 (NKp44-pep8) fused to cell-penetrating peptides (CPPs) can be employed for targeting the intracellular PCNA for the purpose of anticancer therapy. Treatment of tumor cells with NKp44-pep8, fused to R11-NLS cell-penetrating peptide (R11-NLS-pep8), reduced cell viability and promoted cell death, in various murine and human cancer cell lines. Administration of R11-NLS-pep8 to tumor-bearing mice suppressed tumor growth in the 4T1 breast cancer and the B16 melanoma in vivo models. We therefore identified the NKp44 binding site to PCNA and further developed an NKp44-peptide-based agent that can inhibit tumor growth through interfering with the function of intracellular PCNA in the tumor cell.

The features of circulating and tumor-infiltrating γδ T cells in melanoma patients display critical perturbations with prognostic impact on clinical outcome

“…Interestingly, the inhibitory form of NKp44 has been found on tumor-infiltrating NK cells, 40 and blocking the interaction NKp44-PCNA results in inhibition of tumor growth including melanoma in mouse models. 41 Hence, NCR can be considered as novel innate immune checkpoints, which, based on our results, offer an exciting potential therapeutic target to manipulate in cancer.…”

Unleashing Natural Killer Cells in the Tumor Microenvironment–The Next Generation of Immunotherapy?

“…Novel NK cell checkpoint ligands expressed on cancer cells could be desirable targets for new immune checkpoint blockers with favorable toxicity profiles compared to other established immune checkpoints (171). Recently, it was demonstrated that the NKp44 isoform1 receptor, a splice variant of the activating NKp44 receptor, can bind membrane proliferating cell nuclear antigen (PCNA) upregulated on cancer cells, inhibiting NK cell activation (293,294). This is a potentially attractive target due to its different expression profile in healthy proliferating cells vs. cancer cells.…”

PCNA has specific functions in regulation of metabolism in haematological cells

“…Cytosolic roles: Multiple cytosolic proteins involved in cellular signaling and metabolism, including glycolytic enzymes, contain APIM or PIP-box motifs (Ohayon et al, 2019;Olaisen et al, 2018;Olaisen et al, 2015), or are found in complex with PCNA (Naryzhny & Lee, 2010;Olaisen et al, 2015;Witko-Sarsat et al, 2010). Studies have shown that impairing PCNA´s scaffold function affects multiple signaling pathways including the PI3K/AKT and MAPK pathways and the cytokine production after toll receptor stimuli (Olaisen et al, 2018;Olaisen et al, 2015;Sogaard et al, 2019), regulation of apoptosis (Müller et al, 2013;Witko-Sarsat et al, 2010;Yin et al, 2015), cytotoxicity of NK cells (Rosental et al, 2011;Shemesh et al, 2018), and cellular defense against ROS (Ohayon et al, 2019).…”