Galectins Are Differentially Expressed in Supratentorial Pilocytic Astrocytomas, Astrocytomas, Anaplastic Astrocytomas and Glioblastomas, and Significantly Modulate Tumor Astrocyte Migration

Abstract

Galectins, a family of mammalian lectins with specificity to β‐galactosides, are involved in growth‐regulatory mechanisms and cell adhesion. A relationship is assumed to exist between the levels of expression of galectins and the level of malignancy in human gliomas. A comparative study of this aspect in the same series of clinical samples is required to prove this hypothesis. Using computer‐assisted microscopy, we quantitatively characterized by immunohistochemistry the levels of expression of galectins‐1, ‐3 and‐8 in 116 human astrocytic tumors of grades I to IV. Extent of transcription of galectins‐1, ‐3, and ‐8 genes was investigated in 8 human glioblastoma cell lines by means of RT‐PCR techniques. Three of these cell lines were grafted into the brains of nude mice in order to characterize in vivo the galectins‐1, ‐3 and ‐8 expression in relation to the patterns of the tumor invasion of the brain. The role of galectin‐1, ‐3 and ‐8 in tumor astrocyte migration was quantitatively determined in vitro by means of computer‐assisted phase‐contrast videomicroscopy. The data indicate that the levels of galectin‐1 and galectin‐3 expression significantly change during the progression of malignancy in human astrocytic tumors, while that of galectin‐8 remains unchanged. These three galectins are involved in tumor astrocyte invasion of the brain parenchyma since their levels of expression are higher in the invasive parts of xenografted glioblastomas than in their less invasive parts. Galectin‐3, galectin‐1, and to a lesser extent galectin‐8, markedly stimulate glioblastoma cell migration in vitro. Since bands for the transcripts of human galectins‐2, ‐4 and ‐9 were apparently less frequent and intense in the 8 human glioblastoma cell lines, this system provides an excellent model to assign defined roles to individual galectins and delineate overlapping and distinct functional aspects.