Immunohistochemistry of the glial fibrillary acidic protein: basic and applied considerations

A clinicopathologic study of 30 cases of oligoastrocytoma including p53 immunohistochemistry

Mixed gliomas have been difficult to define and subsequently diagnose due to the paucity of literature specifically examining this group of tumors. Thirty mixed gliomas in which the minor glial component comprised at least 20% of the total tumor were studied: 20 oligoastrocytomas (OA) and ten malignant oligoastrocytomas (MOA). Nineteen patients were male (mean age 36 years) and 19 patients (63%) presented with seizures. The tumor was located in the frontal lobe in 17 patients (57%) and the temporal lobe in nine patients (30%). The duration of preoperative symptoms in 25 patients ranged from five days to 14 years (mean 2.6 years). A mean follow-up of four years was available in 29 patients. Fourteen patients, seven with OA and seven with MOA, had recurrent tumor. One patient with MOA and four patients with OA (three with tumor progression and one with extensive leptomeningeal spread) died as a result of their tumor one to five years after diagnosis. Eighteen patients received chemotherapy and/or radiation therapy. Twenty-five tumors were immunostained with antibody to p53 protein. p53 nuclear staining was seen in 5/16 OA (31%) and 3/9 MOA (33%). Positive staining was observed only in astrocytic appearing cells. One of the four patients who died with OA was p53 positive. Three recurrent MOAs were p53 positive. Our study indicates that: 1. mixed gliomas most frequently occur in the frontal lobe and the majority of patients present with seizures; 2. there is no obvious association of p53 detection in mixed gliomas with tumor grade or behavior; and 3. similar to pure fibrillary astrocytomas, a subset of OA and MOA may be associated with p53 alterations.

The dephosphorylation of glial fibrillary acidic protein (GFAP) in the immature rat hippocampus is catalyzed mainly by a type 1 protein phosphatase

We used protein phosphatase inhibitors to study the phosphatase activity involved in the dephosphorylation of the astrocyte marker glial fibrillary acidic protein (GFAP) in a cytoskeletal fraction and in slices prepared from hippocampi of immature rats. Cytoskeletal proteins were labelled with [gamma 32P]ATP in the presence of Ca2+ and calmodulin and then allowed to dephosphorylate through the activity of bound protein phosphatases. Dephosphorylation was inhibited by the protein phosphatase inhibitors okadaic acid and microcystin-LR, but not by EGTA. Maximal inhibition was given by 1 microM okadaic acid and 10 nM microcystin-LR. This difference of two orders of magnitude in the sensitivity of the dephosphorylation to the inhibitors indicates that the bound dephosphorylating activity in the cytoskeletal fraction was due to a type 1 protein phosphatase, rather than protein phosphatase 2A which is equally sensitive to okadaic acid and microcystin-LR. To investigate the dephosphorylation of GFAP in intact tissue we incubated slices with various concentrations of the cell-permeable inhibitor okadaic acid in the presence of [32P] phosphate. Net [32P]-incorporation into GFAP was increased by okadaic acid due to inhibition of dephosphorylation; the minimum effective concentration was 25 nM. Since the IC50 for inhibition of protein phosphatase 2A by okadaic acid is 0.1 nM, this result indicates that in intact tissue GFAP dephosphorylation is primarily due to a type 1 protein phosphatase.

Glial fibrillary acidic protein mRNA increases at proestrus in the arcuate nucleus of mice

Glial fibrillary acidic protein (GFAP) increases during proestrus in astrocytes of the hypothalamic arcuate nucleus (ARC). These changes are associated with altered astrocyte-neuron contacts and synaptic remodelling, during preparation for the preovulatory gonadotrophin surge. This study of young C57BL/6J mice showed transient elevations of GFAP mRNA on proestrus in the ARC by in situ hybridization. Basal GFAP mRNA was regained within 18 h. We hypothesize that changes in astrocytic GFAP on proestrus result from elevations of GFAP mRNA that are, in turn, driven by ovarian secretions of estradiol.