Comparison of L1 expression and secretion in glioblastoma and neuroblastoma cells

Abstract

The expression of cell adhesion molecule L1 has been identified in a vast spectrum of tumors; however, its expression pattern with regard to tumor type is rarely discussed. In the present study, we studied L1 levels in human glioblastomas and neuroblastomas, and compared the expression and secretion of L1 in human glioblastoma U87-MG and neuroblastoma SK-N-SH cells. Immunofluorescence staining revealed different grades of L1 staining in human glioblastoma and neuroblastoma samples. In U87-MG cells, full-length L1 was weakly detected in cell lysates (CLs), while greater levels of abundant soluble L1 were confined in conditioned culture medium (CCM). In contrast, higher levels of full-length L1 were confined in SK-N-SH CLs, while almost no soluble forms of L1 were detected in CCM. Our data indicates various expression patterns of L1 in U87-MG and SK-N-SH cells, which may underlie the different malignancies of the two neural tumor types and further stress the importance of soluble L1-mediated signaling pathways in cell malignancy.

Figure 1.

Schematic diagram demonstrating the homophilic and heterophilic interaction of L1 in U87-MG glioblastoma and SK-N-SH neuroblastoma cells. Ig, immunoglobulin; FN, fibronectin; TM, transmembrane protein; ICD, intracellular domain.

Figure 2.

Representative immunofluorescence staining of L1 in human glioblastoma and neuroblastoma tissues. Human glioblastoma tissues demonstrated extensive positive staining for L1 in the glioblastoma cells and the cell matrix. Human neuroblastoma tissues demonstrated extensive positive staining for L1 at or around the cell membrane. Scale bars, 40 μm. DAPI, 4′,6-diamidino-2-phenylindole.

Figure 3.

Western blot analysis of full-length L1 and released soluble L1 expression in glioblastoma U87-MG and neuroblastoma SK-N-SH cells. (A) In U87-MG cells, full-length L1 in the CL was weakly detected, while the level of soluble L1 in the CCM was markedly high. (B) Released soluble L1 levels were significantly higher compared to those of membrane-tethered full-length L1 in U87-MG cells. (C) In contrast, full-length L1 in the SK-N-SH CL was strongly detected, while soluble L1 in the CCM was almost undetectable. (D) Full-length L1 levels were significantly higher compared to those of released soluble L1 in SK-N-SH cells. (E) The ratio of soluble L1 to full-length L1 in U87-MG cells was significantly higher than that in SK-N-SH cells. GAPDH was used to indicate the equal loading volume and ensure no significant cell leaking into the CCM. ^*P<0.05; ^#P<0.01; n=3. CL, cell lysate; CCM, conditioned culture medium; GAPDH, glyceraldehyde 3-phosphate dehydrogenase.