Clinicopathological and Prognostic Significance of CD44s and CD44v6 Expression in Patients with Glioma: A Systematic Review and Meta-analysis

Background: Cancer stem cell surface marker CD44 has been revealed to promote tumor growth, progression, and metastasis in gliomas. Although the prognostic and clinicopathological value of CD44 standard form (CD44s) and its variant isoform CD44v6 expression in glioma patients has been evaluated in several independent studies, their results remained controversial. Therefore, we performed this meta-analysis to investigate the prognostic and clinicopathological association of CD44s/CD44v6 expression with glioma patients.Methods: A comprehensive literature search was performed in the electronic databases PubMed, EMBASE, Web of Science, the Cochrane Library, China National Knowledge Infrastructure (CNKI), and the Wangfang Data. The statistical analysis was conducted using Stata 15.0 and Review Manager 5.3.Results: A total of 43 studies with 2817 glioma patients were included in this meta-analysis. Pooled results indicated that positive expression of CD44s was significantly associated with poorer overall survival (OS, univariate analysis, HR =1.63, 95% CI= [1.16–2.29], P=0.005; multivariate analysis, HR=2.14, 95%CI= [1.21, 3.78], P=0.009), and reduced progression-free survival (PFS) in the univariate analysis (HR=2.09, 95% CI= [1.59, 2.75], P<0.00001), but not with PFS in the multivariate analysis (P>0.05) or tumor recurrence (P>0.05). CD44 expression was significantly upregulated in glioma tissues when compared with non-tumorous brain tissues (CD44s, OR=31.31, 95% CI= [15.22, 64.43], P<0.00001; CD44v6, OR=13.18, 95% CI= [5.51, 31.51], P<0.00001). In particular, CD44 expression was preferentially expressed in high-grade gliomas (grade III-IV vs. grade I-II, CD44s, OR=4.67, 95% CI= [3.18, 6.87], P<0.00001; CD44v6, OR=2.06, 95% CI= [1.21, 3.51], P=0.008). CD44s expression was lower in brain metastases than that in primary gliomas (OR=0.25, 95% CI= [0.10, 0.60], P=0.002), however, higher expression of CD44v6 was detected in brain metastases when compared with primary gliomas (OR=49.44, 95% CI= [13.06, 187.22], P<0.00001).Conclusions:This meta-analysis revealed the prognostic value of CD44s expression and clinicopathological significance of CD44s/CD44v6 expression in gliomas. Increased CD44s expression can predict worse prognosis of glioma patients. Particularly, CD44s is an independent prognostic factor for poor OS of glioma patients. Both CD44s and CD44v6 were glioma patients predominantly expressed in glioma tissues, especially in high-grade gliomas. Additionally, CD44v6 is a potential diagnostic biomarker for differentiating brain metastases from primary gliomas in individual cases. Therapeutic strategies targeting CD44 in gliomas should be further explored in the future.

CD44s Assembles Hyaluronan Coat on Filopodia and Extracellular Vesicles and Induces Tumorigenicity of MKN74 Gastric Carcinoma Cells

CD44 is a multifunctional adhesion molecule typically upregulated in malignant, inflamed and injured tissues. Due to its ability to bind multiple ligands present in the tumor microenvironment, it promotes multiple cellular functions related to tumorigenesis. Recent data has shown that CD44 and its principal ligand hyaluronan (HA) are carried by extracellular vesicles (EV) derived from stem and tumor cells, but the role of CD44 in EV shedding has not been studied so far. To answer this question, we utilized CD44-negative human gastric carcinoma cell line MKN74 manipulated to stably express CD44 standard form (CD44s). The effect of CD44s expression on HA metabolism, EV secretion, morphology and growth of these cells was studied. Interestingly, HAS2 and HYAL2 expression levels were significantly upregulated in CD44s-expressing cells. Cell-associated HA levels were significantly increased, while HA levels in the culture medium of CD44s-positive cells was lower compared to CD44s-negative MOCK cells. CD44s expression had no significant effect on the proliferation capacity of cells, but cells showed diminished contact inhibition. Superresolution imaging revealed that CD44s and HA were accumulated on filopodia and EVs secreted from CD44s-positive cells, but no differences in total numbers of secreted EV between CD44s-negative and -positive cells was detected. In 3D cultures, CD44s-expressing cells had an enhanced invasion capacity in BME gel and increased spheroidal growth when cultured in collagen I gel. No significant differences in mitotic activity, tumor size or morphology were detected in CAM assays. However, a significant increase in HA staining coverage was detected in CD44s-positive tumors. Interestingly, CD44s-positive EVs embedded in HA-rich matrix were detected in the stromal areas of tumors. The results indicate that CD44s expression significantly increases the HA binding capacity of gastric cancer cells, while the secreted HA is downregulated. CD44s is also carried by EVs secreted by CD44s-expressing cells. These findings highlight the potential usefulness of CD44s and its ligands as multipurpose EV biomarkers, because they are upregulated in inflammatory, injured, and cancer cells and accumulate on the surface of EVs secreted in these situations.