The Impact of Glycosylation on the Functional Activity of CD133 and the Accuracy of Its Immunodetection

The membrane glycoprotein CD133 (prominin-1) is widely regarded as the main molecular marker of cancer stem cells, which are the most malignant cell subpopulation within the tumor, responsible for tumor growth and metastasis. For this reason, CD133 is considered a promising prognostic biomarker and molecular target for antitumor therapy. Under normal conditions, CD133 is present on the cell membrane in glycosylated form. However, in malignancies, altered glycosylation apparently leads to changes in the functional activity of CD133 and the availability of some of its epitopes for antibodies. This review focuses on CD133's glycosylation in human cells and its impact on the function of this glycoprotein. The association of CD133 with proliferation, differentiation, apoptosis, autophagy, epithelial-mesenchymal transition, the organization of plasma membrane protrusions and extracellular trafficking is discussed. In this review, particular attention is paid to the influence of CD133's glycosylation on its immunodetection. A list of commercially available and custom antibodies with their characteristics is provided. The available data indicate that the development of CD133-based biomedical technologies should include an assessment of CD133's glycosylation in each tumor type.

[Is it possible to detect surface antigen CD133 on patient-derived glioblastoma continuous cell cultures using fluorescent aptamers?]

Theranostics combines diagnostics and therapeutic exposure. Regarding glioblastomas, theranostics solves the problem of detecting and destroying tumor stem cells resistant to irradiation and chemotherapy and causing tumor recurrence. Transmembrane surface antigen CD133 is considered as a potential marker of tumor stem cells.

OBJECTIVE

To detect CD133 in patient-derived glioblastoma continuous cell cultures using fluorescence microscopy and modified aptamers (molecular recognition elements) anti-CD133.

MATERIAL AND METHODS

To detect CD133, we used mousey fluorescence monoclonal antibodies anti-CD133 MA1-219, FAM-modified DNA aptamers anti-CD133 AP-1-M and Cs5. Non-aptamer DNA oligonucleotide NADO was used as a negative control. Detection was performed for three samples of patient-derived glioblastoma continuous cell cultures coded as 1548, 1721 and 1793.

RESULTS

MA1-219 antibodies brightly stained cell culture 1548, to a lesser extent - 1721. There was diffuse staining of cell culture 1793. Cs5-FAM aptamer stained cells in a similar way, but much weaker. AP-1-M-FAM aptamer interacted with cells even weaker and diffusely stained only cell culture 1793. Non-aptamer NADO did not stain cell culture 1548 and very weakly diffusely stained cell culture 1793.

CONCLUSION

For both molecular recognition elements (MA1-219 antibody and Cs5 aptamer), 3 cell culture samples can be arranged in the following order possibly reflecting CD133 status decrease: strong signal for cell culture 1548, much weaker for 1721, even weaker for 1793. Only cell culture 1548 can be considered CD133 positive with combination of Cs5+ and NADO signals. Cell culture 1793 is CD133 false positive with combination of Cs5+ and NADO+ signals.

Can CD133 Be Regarded as a Prognostic Biomarker in Oncology: Pros and Cons

The CD133 cell membrane glycoprotein, also termed prominin-1, is expressed on some of the tumor cells of both solid and blood malignancies. The CD133-positive tumor cells were shown to exhibit higher proliferative activity, greater chemo- and radioresistance, and enhanced tumorigenicity compared to their CD133-negative counterparts. For this reason, CD133 is regarded as a potential prognostic biomarker in oncology. The CD133-positive cells are related to the cancer stem cell subpopulation in many types of cancer. Recent studies demonstrated the involvement of CD133 in the regulation of proliferation, autophagy, and apoptosis in cancer cells. There is also evidence of its participation in the epithelial-mesenchymal transition associated with tumor progression. For a number of malignant tumor types, high CD133 expression is associated with poor prognosis, and the prognostic significance of CD133 has been confirmed in a number of meta-analyses. However, some published papers suggest that CD133 has no prognostic significance or even demonstrate a certain correlation between high CD133 levels and a positive prognosis. This review summarizes and discusses the existing evidence for and against the prognostic significance of CD133 in cancer. We also consider possible reasons for conflicting findings from the studies of the clinical significance of CD133.