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Epidermal growth factor differentially regulates low density lipoprotein receptor–related protein gene expression in neoplastic and fetal human astrocytes
Author(s) -
Hussaini Isa M.,
Brown Morry D.,
Karns Larry R.,
Carpenter Joan,
Redpath Gerald T.,
Gonias Steven L.,
Vandenberg Scott R.
Publication year - 1999
Publication title -
glia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.954
H-Index - 164
eISSN - 1098-1136
pISSN - 0894-1491
DOI - 10.1002/(sici)1098-1136(19990101)25:1<71::aid-glia7>3.0.co;2-0
Subject(s) - biology , epidermal growth factor , receptor , ldl receptor , astrocyte , endocytosis , cell culture , neuroglia , microbiology and biotechnology , endocrinology , medicine , lipoprotein , biochemistry , central nervous system , cholesterol , genetics
Low density lipoprotein receptor–related protein (LRP) is a multi‐functional 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 α 2 ‐macroglobulin (α 2 M*) on intact cells and by Western and Northern blot analyses of cell extracts. Primary cultured astrocytes expressed the highest levels of α 2 M*‐binding capacity (B max = 30 fmol/mg protein). This was twofold higher than for the U‐1242 MG astrocytoma cells (B max = 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 B max 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 TGFα (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. GLIA 25:71–84, 1999. © 1999 Wiley‐Liss, Inc.