Differential expression of stem cell markers and vascular endothelial growth factor in human retinoblastoma tissue

Abstract

Purpose: To investigate the relationship between vascular endothelial growth factor (VEGF) and the cancer stem cell-vascular niche complex in human retinoblastoma tissue.

Methods: Six human retinoblastoma specimens primarily enucleated for Reese-Ellsworth classification stage 5a were stained to detect cancer stem cell markers, including ABCG2 for the stem cell marker and MCM2 for the neural stem cell marker, as well as to detect VEGF for the angiogenic cytokine. Using immunofluorescence, the expression of these proteins was analyzed, and their relative locations noted.

Results: In non-neoplastic retina of tumor-bearing eyes, ABCG2 and MCM2 were sporadically expressed in the ganglion cell layer and the inner nuclear layer, whereas VEGF was sporadically expressed in inner retina where retinal vessels are abundantly distributed. In the tumor, ABCG2 was strongly expressed out of Wintersteiner rosettes, whereas MCM2 and VEGF were strongly stained in the rosettes. Interestingly, the outer portion of the rosettes was positive for MCM2, and the inner portion of the rosettes was positive for VEGF.

Conclusions: Our data demonstrated that MCM2 and VEGF are strongly expressed in the rosettes of the tumor, which were far from the area of ABCG2-positive cells. Although VEGF might not directly contribute to the cancer stem cell-vascular niche complex, it could play some role in the differentiation of tumor cells to build up the rosettes.

Keywords: Biological tumor markers; Neoplastic stem cells; Retinoblastoma; Vascular endothelial growth factors.

Fig. 1

ABCG2, MCM2, and VEGF expression in the non-neoplastic retina of the human retinoblastoma eye. (A) ABCG2 was sporadically expressed in the ganglion cell layer and the inner nuclear layer. Original magnification ×20. (B) MCM2 positivity was observed in GCL and INL, similar to ABCG2. Original magnification ×20. (C) VEGF was also sporadically expressed in the inner retina. Original magnification ×20. VEFG=vascular endothelial growth factor; GCL=ganglion cell layer; IPL=inner plexiform layer; INL=inner nuclear layer; OPL=outer plexiform layer; ONL=outer nuclear layer.

Fig. 2

ABCG2, MCM2, and VEGF expression in retinoblastoma tumors. (A and B) ABCG2 was expressed outside of the Wintersteiner rosettes or tumor lobules. (C and D) MCM2 was strongly expressed in the rosettes and lobules, especially in the outer portion of the rosettes. (E and F) VEGF positivity was also observed in the rosettes of lobules, specifically in the inner portion of the rosettes. Original magnification ×20 with A, C, and E. Original magnification ×40 with B, D, and F.