CD47 blockade enhances cisplatin sensitivity by inhibiting DNA repair gene expression

Abstract

CD47, a cell surface transmembrane glycoprotein, is an innate immune checkpoint that suppresses phagocytic clearance. Emerging evidence suggests that CD47 has noncanonical functions. However, its involvement in chemotherapy resistance is not well understood. Our study reveals that cisplatin treatment upregulates CD47 expression across multiple cancer cell lines. Cisplatin induces the expression of CD47 through the ATM/NF-κB signaling pathway. Genetic ablation of CD47 dramatically sensitizes cancer cells to cisplatin. Mechanistically, CD47 depletion potentiates cisplatin-induced DNA damage, as demonstrated by elevated γH2AX formation and ATM phosphorylation. Knockdown of CD47 inhibits the expression of DNA repair genes ERCC1, FANCA, and BRCA2 through the ATM/NF-κB pathway. Remarkably, CD47 blockade with neutralizing antibodies recapitulates these effects, synergistically potentiating cisplatin’s DNA-damaging capacity while suppressing DNA repair capacity. CD47 blockade also potentiates cisplatin’s tumor inhibitory effect in vivo. These findings establish a novel mechanism whereby CD47 promotes cisplatin resistance through transcriptional regulation of DNA repair pathway, providing rationale for combining CD47-targeted therapies with conventional chemotherapy. This dual approach could simultaneously overcome immune evasion while enhancing treatment efficacy.

1. Introduction

CD47 is a cell surface transmembrane glycoprotein. It binds to the signal regulatory protein (SIRP) on the surface of macrophages to prevent phagocytosis. It is widely expressed on many cells of epithelial and mesenchymal origin and is constitutively overexpressed in many tumors [1]. Expression of CD47 on cancer cells may allow cancer cells to escape macrophage phagocytosis and immune surveillance of the body [2–6]. High CD47 expression on tumor cells is associated with poor prognosis in human malignancies [7,8].

Blocking CD47 signaling or suppressing CD47 expression protects normal tissues from ionizing radiation (IR) injury [9–11]. CD47 deficiency protects irradiated T-cells and endothelial cells [12] and both hematopoietic and gastrointestinal tissue [11] from radiation by activation of autophagy, anabolic metabolites [10], transcription factors that support asymmetric stem cell self-renewal [13], and SLFN11 expression [14]. It has been shown that non-malignant cells and Jurkat T cells lacking CD47 are protected from genotoxic stress induced by IR [10,12]. This protection is mediated in part by an enhanced protective autophagy response in cells lacking CD47 or with reduced CD47 expression [12]. Radioresistance in the CD47-deficient mutant is associated with global metabolic stabilization, including induction of nucleotide biosynthesis required to repair DNA damage induced by ionizing radiation [10]. Loss of CD47 or blocking its function with the CD47 function-blocking antibody B6H12 improved the ability of Jurkat T cells to restore genomic integrity after damage caused by IR [14]. However, the relationship between IR, DNA damage and CD47 expression, has not been studied yet. Ghantous et al. [15] demonstrated recently that IR and genotoxic agents-caused DNA damage induced CD47 expression in both non-malignant and malignant cells. The authors showed that genotoxic stress upregulated CD47 following DNA damage in a MRE11-dependent manner.

Contrary to its protective effect in normal cells, CD47 loss has been shown to enhance radiosensitivity and chemosensitivity in cancer cells. Inhibition of CD47 sensitized the B16 mouse melanoma cells to IR injury in vivo [9]. CD47 expression was upregulated in chemoresistant hepatocellular carcinoma (HCC), and suppression of CD47 sensitized HCC to doxorubicin in vivo through blockade of CTSS/PAR2 signaling [16]. Knockdown of CD47 in liver cancer Huh-7 and MHCC97L cells increased the sensitivity of the cells to both cisplatin and doxorubicin. CD47+ HCC cells derived from PLC/PRF/5 were more chemoresistant than CD47-null cells in response to cisplatin and doxorubicin treatments. Upregulated CD47 made HCC resistant to sorafenib, though the underlying mechanism is unknown [17]. Expression of CD47 in ovarian clear cell carcinoma correlated with chemotherapy resistance and prognosis [18]. Knockdown of CD47 enhanced the sensitivity of breast cancer MDA-MB-231 cells to docetaxel [19]. These studies indicate that CD47 confers cancer cell resistance to chemotherapy. However, in B-cell chronic lymphocytic leukemia cells, CD47 activation induced cell apoptosis [20]. And CD47 activation mediated killing of breast cancer cells [21]. Analysis of B16 melanoma cells exposed to irradiation revealed that suppression of CD47 exerted a radioprotective effect for cell viability in vitro, which is