A Comparative in Silico Analysis of CD24's Prognostic Value in Human and Canine Prostate Cancer

Abstract

CD24 is a cell surface molecule anchored by glycosyl-phosphatidyl-inositol and expressed by different human cancers, including prostate cancer (PC). Some studies have demonstrated that CD24 expression is associated with poor patient outcome; however, few studies have investigated CD24 expression in spontaneous animal models of human PC, such as canine PC. This study aimed to evaluate the expression of CD24 in human PC using the in silico analysis of the data obtained from The Cancer Genome Atlas (TCGA) and comparing it with the previously published prostatic canine transcriptome data. In addition, CD24 expression was confirmed by immunohistochemistry in an independent cohort of canine prostatic samples and its prognostic significance assessed. The systematic review identified 10 publications fitting with the inclusion criteria of this study. Of the 10 manuscripts, 5 demonstrated a direct correlation between CD24 overexpression and patient prognoses. CD24 expression was also associated with PSA relapse (2/5) and tumor progression (1/5). However, the in silico analysis did not validate CD24 as a prognostic factor of human PC. Regarding canine PC, 10 out of 30 normal prostates and 27 out of 40 PC samples were positive for CD24. As in humans, there was no association with overall survival. Overall, our results demonstrated a significant CD24 overexpression in human and canine prostate cancer, although its prognostic value may be questionable. However, tumors overexpressing CD24 may be a reliable model for new target therapies and dogs could be used of a unique preclinical model for these studies.

Keywords: CD24; carcinoma; comparative oncology; dog; prostate.

Figure 1

Schematic representation of the study design. (1) Systematic review of the previous literature and selection of manuscripts evaluating prognostic significance of CD24 in human prostate cancer. (2) In silico analysis to evaluate CD24 expression in prostate cancer compared to normal prostate (as found by Gene Expression Profiling Interactive Analysis (GEPIA)) and association between CD24 and patients’ survival (GEPIA and The Human Protein Atlas (THPA)). (3) Retrieval of CD24 immunohistochemistry slides from two previous veterinary studies and re-evaluation of the CD24 expression in association with clinical pathological characteristics. Figure generated in BioRender (www.biorender.com, accessed on 15 November 2020).

Figure 2

CD24 gene and protein expression in human prostate cancer. (A): Tissue microarray (TMA) core from a normal human prostate gland. Normal glandular cells show moderate membranous and cytoplasmic expression. (B): A TMA core from a human prostate cancer, with a strong CD24 expression in the membrane and cytoplasm of neoplastic cells. (C): CD24 overexpression in prostate cancer samples compared to normal samples (* p > 0.01). Image credit of the immunohistochemistry images: Human Protein Atlas, www.proteinatlas.org. Image available at the following URL: https://v20.proteinatlas.org/ENSG00000272398-CD24/tissue (accessed on 15 November 2020). The gene expression dotplot was generated using GEPIA database (http://gepia.cancer-pku.cn/about.html, accessed on 15 November 2020). PRAD: Prostate cancer dataset.

Figure 3

Survival analysis of human patients according to CD24 expression. (A): CD24 expression is not associated with overall survival of human prostate cancer patients. (B): the disease-free interval is not associated with CD24 expression. The survival curves were generated using the GEPIA database (http://gepia.cancer-pku.cn/about.html, accessed on 15 November 2020).

Figure 4

Survival association according to the CD24 fragments per kilobase of exon model per million reads mapped (FPKM). The median of CD24 FPKM in the group of dead human patients is 78 and in the group of living human patients is 83. There is no significant association between CD24 expression and overall survival (p > 0.05). Image credit: Human Protein Atlas, www.proteinatlas.org accessed on 15 November 2020. Image available at the following URL: https://v20.proteinatlas.org/ENSG00000272398-CD24/pathology/prostate+cancer#, accessed on 15 November 2020.

Figure 5

CD24 immunoexpression in canine prostate cancer. (A): multifocal cytoplasmic CD24 expression (arrows) in a normal prostate considered positive for CD24. (B): canine prostate cancer showing diffuse cytoplasmic and membranous CD24 expression by neoplastic cells. (C): CD24 overexpression in canine prostate cancer compared to normal prostate. (D): Survival analysis according to CD24 expression. Dogs with CD24 positive expression showed a tendency to lower survival compared to dogs with CD24 negative expression.

Figure 6

CD24 tertiary protein structure in dogs (A) and humans (B). Human and canine CD24 proteins showed a 90% similarity among amino acid sequence and also similar tyrosine kinase domains. Figures generated in Swiss model online tool (https://swissmodel.expasy.org/, accessed on 15 November 2020).

Figure 7

CD24 immunofluorescence on canine (PC1 and PC2) and human (PC3) prostate cancer cell lines. CD24 positive expression was observed in both canine and human cells, demonstrating the potential of these cells to be preclinical models for CD24-targeting drugs.