lactoferrin and Astrocytoma

Low density lipoprotein receptor-related protein (LRP) is a multifunctional endocytotic receptor that may modify the biological activity of reactive astrocytes in neuroplasticity and neurodegeneration and of malignant astrocytes in brain invasion. In this study, the regulation of LRP by epidermal growth factor receptor (EGFR) ligands in both cultured human fetal astrocytes and astrocytic tumor cell lines (U-251 MG and U-1242 MG) was investigated. All astrocytic cell types expressed LRP, as determined by the binding of activated alpha2-macroglobulin (alpha2M*) on intact cells and by Western and Northern blot analyses of cell extracts. Primary cultured astrocytes expressed the highest levels of alpha2M*-binding capacity (Bmax = 30 fmol/mg protein). This was twofold higher than for the U-1242 MG astrocytoma cells (Bmax = 15 fmol/mg protein) and fourfold greater than for the glioblastoma U-251 MG cells (7.0 fmol/mg protein). Receptor affinity (K(D)) ranged from 0.25 to 0.6 nM in all the astroglial cell types. Functional LRP at the surface was down-regulated by EGF, compared with controls, as indicated by a reduction of both Bmax and LRP-mediated endocytosis by approximately 50% and 60%, respectively. In comparison, EGF treatment of primary astrocytes did not down-regulate LRP expression or LRP-mediated endocytosis. Treatment of the tumor cells with EGF or TGFalpha (25 ng/ml) significantly down-regulated total cellular LRP. Receptor-associated protein (RAP) mRNA expression was not affected by EGF in either tumor cells or primary astrocytes. The reduction of LRP in the tumor cells resulted from a specific decrease in LRP mRNA transcription, as determined by Northern blot and nuclear run-on experiments. These data suggest that EGF mediates a functional down-regulation of LRP endocytotic activity in astrocytic tumor cells and that LRP expression is differentially regulated in neoplastic and non-neoplastic astrocytes.

Topics: alpha-Macroglobulins; Astrocytes; Astrocytoma; Blotting, Northern; Blotting, Western; Brain Neoplasms; Calcium-Calmodulin-Dependent Protein Kinases; Cell Membrane; Cell Nucleus; Cells, Cultured; Endocytosis; Epidermal Growth Factor; ErbB Receptors; Gene Expression Regulation; Glial Fibrillary Acidic Protein; Humans; Lactoferrin; Receptors, LDL; RNA

The presence of lactoferrin in astrocytomas, anaplastic astrocytomas and multiforme glioblastomas was determined by immunohistochemistry; the staining intensity and the percentage of neoplastic stained cells were graded and statistical analysis was performed by non-parametric methods. A moderate to strong diffuse immunoreactivity for lactoferrin was shown in glial elements of astrocytomas, while the positivity was progressively reduced in anaplastic astrocytomas and in multiforme glioblastomas, some of which were unstained; a highly significant difference was found between scores relative to astrocytomas and glioblastomas. We suggest that the lactoferrin may be produced by neoplastic astrocytes which permits a greater availability of iron for metabolic cellular processes. Alternatively, the cytoplasmic localization of lactoferrin in neoplastic astrocytes may be the consequence of defective or functionally impaired lactoferrin receptors at the cellular surface.

Topics: Astrocytoma; Brain Neoplasms; Female; Glioblastoma; Humans; Immunohistochemistry; Iron; Lactoferrin; Male; Middle Aged; Staining and Labeling