Primary cortical astrocytes were isolated from normal (+/+), heterozygous (+/-), or homozygous (-/-) p53-knockout mice. The normal astrocytes grew slowly and underwent crisis after limited division, while the homozygously defective cells grew rapidly and without contact inhibition. These -/- cells could not initially form colonies in soft agarose but acquired this capability after 10 passages in FCS or basic fibroblast growth factor but not epidermal growth factor. Almost all -/- astrocytes weakly expressed glial fibrillary acidic protein at passage 10 and were also A2B5+ when cultured in basic fibroblast growth factor. Most heterozygous cells resembled normal ones; however, some survived crisis, grew rapidly, and formed colonies. Outgrowing cells had all lost the wild-type p53 allele. These molecular and cellular events mimic the early stages of human brain tumors, suggest a role for p53 in the earliest stages of disease progression, and provide an experimental system to analyze the effects of other tumor-specific mutations in the disease process.

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Supported by the California Division of the American Cancer Society, Fellowship 1-62-95 (to O. B.).

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