The Vitamin B12 Receptor CD320 Is a Key Metabolic Dependency and Prognostic Biomarker in Hepatocellular Carcinoma
DOI:
https://doi.org/10.54097/wzcyfb37Keywords:
Hepatocellular Carcinoma (HCC); Vitamin B12; CD320; Tumor Microenvironment; Immunometabolism; Metabolic Competition; Natural Killer (NK) Cells.Abstract
Background: Hepatocellular carcinoma (HCC) is a leading cause of cancer-related death globally, and its immunosuppressive tumor microenvironment (TME) often limits the efficacy of immunotherapies. Metabolic competition between cancer cells and immune cells for essential nutrients is a critical mechanism of immune evasion. Vitamin B12 (VB12), a micronutrient vital for cellular proliferation and metabolism, is acquired by cells via the transcobalamin receptor, CD320. We hypothesized that HCC cells overexpress CD320 to sequester VB12, thereby fueling their own proliferation while simultaneously depriving anti-tumor immune cells, such as Natural Killer (NK) cells, of this crucial cofactor. Methods: We conducted a comprehensive bioinformatic analysis of bulk and single-cell RNA sequencing data from HCC patient cohorts to evaluate CD320 expression and its clinical significance. In vitro experiments were performed using human HCC cell lines (e.g., HepG2) and a non-malignant hepatocyte line. CD320 expression was validated at the mRNA and protein levels using RT-qPCR and Western blotting. The functional role of CD320 was investigated through siRNA-mediated gene silencing, followed by proliferation assays (MTT) in VB12-replete and VB12-deficient conditions. Results: Our analysis revealed that CD320 expression is significantly upregulated in HCC tissues compared to adjacent normal liver tissues. Elevated CD320 levels were strongly correlated with advanced clinical stage and significantly poorer overall survival in HCC patients. Single-cell transcriptomic analysis confirmed that this overexpression is predominantly driven by malignant cells, rather than by immune or stromal components of the TME. Functionally, silencing CD320 in HepG2 cells markedly attenuated their proliferative capacity. While supplemental VB12 robustly promoted the growth of control cells, this effect was completely abrogated in CD320-knockdown cells, demonstrating a critical dependence of HCC proliferation on the CD320-VB12 uptake axis. Conclusion: This study identifies the Vitamin B12 receptor, CD320, as a novel prognostic biomarker and a key mediator of proliferation in hepatocellular carcinoma. Our findings support a model in which HCC cells hijack the VB12 metabolic pathway by overexpressing CD320. This adaptation provides a competitive advantage for nutrient acquisition, which fuels tumor growth and is hypothesized to create a nutrient-deprived microenvironment that impairs anti-tumor immunity. The CD320-VB12 axis represents a promising therapeutic vulnerability, and targeting this pathway may offer a dual strategy to directly inhibit cancer cell proliferation and restore immune function in the TME.
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