Expression patterns of Wnt signaling component, secreted frizzled‑related protein 3 in astrocytoma and glioblastoma

Abstract

Secreted frizzled-related protein 3 (SFRP3) is a member of the family of soluble proteins, which modulate the Wnt signaling cascade. Novel research has identified aberrant expression of SFRPs in different types of cancer. In the present study the expression intensities and localizations of the SFRP3 protein across different histopathological grades of astrocytic brain tumors were investigated by immunohistochemistry, digital scanning and image analysis. The results demonstrated that the differences between expression levels and malignancy grades were statistically significant. Tumors were classified into four malignancy grades according to the World Health Organization guidelines. Moderate (P=0.014) and strong (P=0.028) nuclear expression levels were significantly different in pilocytic (grade I) and diffuse (grade II) astrocytomas demonstrating higher expression values, as compared with anaplastic astrocytoma (grade III) and glioblastoma (grade IV). When the sample was divided into two groups, the moderate and high cytoplasmic expression levels were observed to be significantly higher in glioblastomas than in the group comprising astrocytoma II and III. Furthermore, the results indicated that high grade tumors were associated with lower values of moderate (P=0.002) and strong (P=0.018) nuclear expression in comparison to low grade tumors. Analysis of cytoplasmic staining demonstrated that strong cytoplasmic expression was significantly higher in the astrocytoma III and IV group than in the astrocytoma I and II group (P=0.048). Furthermore, lower grade astrocytomas exhibited reduced membranous SFRP3 staining when compared with higher grade astrocytomas and this difference was statistically significant (P=0.036). The present results demonstrated that SFRP3 protein expression levels were decreased in the nucleus in higher grade astrocytoma (indicating the expected behavior of an antagonist of Wnt signaling), whereas when the SFRP3 was located in the cytoplasm an increased expression level of SFRP3 was identified in the high grade astrocytomas when compared with those of a low grade. This may suggest that SFRP3 acts as an agonist of Wnt signaling and promotes invasive behavior.

Figure 1

Characteristic immunohistochemical staining of different SFRP3 expression levels. (A) Diffuse astrocytoma showing strong nuclear staining, (B) anaplastic astrocytoma exhibiting moderate cytoplasmic expression, (C) glioblastoma demonstrating strong cytoplasmic staining, and (D) glioblastoma showing cytoplasmic and membranous staining (arrows). Scale bar: (A–C) 50 µm; (D) 20 µm.

Figure 2

Graphs demonstrating moderate and strong levels of secreted frizzled-related protein 3 expression in different grades of astrocytic brain tumor. (A) Nuclear and (B) cytoplasmic expression. (A) High grade tumors (A III and G IV) exhibited significantly lower mean values of both moderate and strong nuclear expression, as compared with the moderate and strong values of low grade tumors (A I and A II) (^*P<0.05). (B) Mean values of moderate and strong cytoplasmic expression for high grade tumors were significantly higher than the mean values of low grade tumors (^*P<0.05). A I, pilocytic astrocytoma; A II, diffuse astrocytoma; A III, anaplastic astrocytoma; G IV, glioblastoma.

Figure 3

Low grade (A I and A II) group demonstrated significantly less membranous localization of secreted frizzled-related protein 3 when compared with the high grade (A III and G IV) group (^*P=0.036). A I, pilocytic astrocytoma; A II, diffuse astrocytoma; A III, anaplastic astrocytoma; G IV, glioblastoma.