A tumor cell specific Zona Pellucida glycoprotein 3 RNA transcript encodes an intracellular cancer antigen

Iman J Schultz; Yvette Zimmerman; Cathy B Moelans; Marcin Chrusciel; Jan Krijgh; Paul J van Diest; Ilpo T Huhtaniemi; Herjan J T Coelingh Bennink

doi:10.3389/fonc.2023.1233039

A tumor cell specific Zona Pellucida glycoprotein 3 RNA transcript encodes an intracellular cancer antigen

Front Oncol. 2023 Dec 6:13:1233039. doi: 10.3389/fonc.2023.1233039. eCollection 2023.

Authors

Iman J Schultz¹, Yvette Zimmerman¹, Cathy B Moelans², Marcin Chrusciel³, Jan Krijgh¹, Paul J van Diest², Ilpo T Huhtaniemi^{3

4}, Herjan J T Coelingh Bennink¹

Affiliations

¹ Pantarhei Oncology BV, Zeist, Netherlands.
² Department of Pathology, University Medical Center Utrecht, Utrecht, Netherlands.
³ Institute of Biomedicine, University of Turku, Turku, Finland.
⁴ Institute of Reproductive and Developmental Biology, Imperial College London, London, United Kingdom.

Abstract

Background: Expression of Zona Pellucida glycoprotein 3 (ZP3) in healthy tissue is restricted to the extracellular Zona Pellucida layer surrounding oocytes of ovarian follicles and to specific cells of the spermatogenic lineage. Ectopic expression of ZP3 has been observed in various types of cancer, rendering it a possible therapeutic target.

Methods: To support its validity as therapeutic target, we extended the cancer related data by investigating ZP3 expression using immunohistochemistry (IHC) of tumor biopsies. We performed a ZP3 transcript specific analysis of publicly available RNA-sequencing (RNA-seq) data of cancer cell lines (CCLs) and tumor and normal tissues, and validated expression data by independent computational analysis and real-time quantitative PCR (qPCR). A correlation between the ZP3 expression level and pathological and clinical parameters was also investigated.

Results: IHC data for several cancer types showed abundant ZP3 protein staining, which was confined to the cytoplasm, contradicting the extracellular protein localization in oocytes. We noticed that an alternative ZP3 RNA transcript, which we term 'ZP3-Cancer', was annotated in gene databases that lacks the genetic information encoding the N-terminal signal peptide that governs entry into the secretory pathway. This explains the intracellular localization of ZP3 in tumor cells. Analysis of publicly available RNA-seq data of 1339 cancer cell lines (CCLs), 10386 tumor tissues (The Cancer Genome Atlas) and 7481 healthy tissues (Genotype-Tissue Expression) indicated that ZP3-Cancer is the dominant ZP3 RNA transcript in tumor cells and is highly enriched in many cancer types, particularly in rectal, ovarian, colorectal, prostate, lung and breast cancer. Expression of ZP3-Cancer in tumor cells was confirmed by qPCR. Higher levels of the ZP3-Cancer transcript were associated with more aggressive tumors and worse survival of patients with various types of cancer.

Conclusion: The cancer-restricted expression of ZP3-Cancer renders it an attractive tumor antigen for the development of a therapeutic cancer vaccine, particularly using mRNA expression technologies.

Keywords: RNA transcript; ZP3; cancer antigen; intracellular; oocyte.