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Effect of retinoids on the proliferation, morphology and expression of glial fibrillary acidic protein of an anaplastic astrocytoma cell line

We studied the effect of retinoids on the growth and differentiation of a cell line (U 343 MG‐A) derived from a human malignant astrocytoma. Cultures treated with all‐trans or 13‐cis retinoic acid showed a dose‐dependent inhibition of proliferation and a marked reduction in the mean cell number at the plateau phase of growth (3.5 × 106 vs. 1 × 107 cells/25 cm<2>) compared with untreated cultures. At confluence, cells treated with all‐trans or 13‐cis retinoic acid were contactinhibited, whereas control cultures showed crowding, piling, and overgrowth. All‐trans retinol or retinyl acetate did not inhibit growth. Astrocytoma cultures treated with all‐trans retinoic acid (10−6 M) for 5 days were modestly growth‐inhibited but by day 16 had the same numbers of cells as controls; cultures that received all‐trans retinoic acid for 9 days were markedly growth‐inhibited for 7 days after the drug was removed. All‐trans and 13‐cis retinoic acid (10−6 M) prevented the EDTA‐induced cell detachment seen in control cultures. Strongly adherent all‐trans retinoic‐acid‐treated astrocytoma cells grew at a slower rate than did readily detached all‐trans retinoic‐acid‐treated or control cells. Cell spreading, an increased cytoplasmic:nuclear ratio, and greater numbers of broadly bipolar cells, some bearing thin cytoplasmic processes, were seen in cultures treated with 10−6 M all‐trans or 13‐cis retinoic acid. Small tightly packed cuboidal cells and large broadly bipolar cells were seen in astrocytoma cultures from which all‐trans retinoic acid was removed on days 5 and 9. Indirect immunofluorescence revealed more intense staining with antiserum to glial fibrillary acidic protein in cultures treated with 10−6 M all‐trans retinoic acid than in control cultures; electron‐microscope examination of similarly treated cultures revealed more abundant 8–10 nm intermediate filaments than in control cultures. An enzyme‐linked immunosorbent assay showed that all‐trans or 13‐cis retinoic acid caused a dose‐dependent increase in the quantity of glial fibrillary acidic protein in the astrocytoma cells.