Selective gene amplification in mammalian cells

• Selective gene amplification in mammalian cells is now recognized as a common cellular response to selection in a number of different toxic drugs, such as methotrexate (MTX). coformycin, PALA, hydroxyurea (HU), vincristine (VCR). colcemid (COL) and actinomycin D (AMD). Recently, we have studied SEWA murine tumor cells in culture exhibiting the pleiotropic drug resistance (PDR) phenotype. Cells subjected to stepwise selection in AMD, VCR or COL all develop double minute chromosomes (DM), which are a cytogenetic expression of gene amplification. These lines overproduce a 21 K acidic soluble protein and show a high degree of cross resistance, which is typical for the PDR phenotype. Other workers have shown that cells with this phenotype exhibit a shift in membrane-bound glycoproteins from 90- 100 K to 150-170 K. Thus, it is likely that several genes are involved in the development of the PDR phenotype. We have isolated a fraction highly enriched in DM from an AMD-resistant SEWA subline. DNA was extracted from this fraction, and several DM-specific DNA-probes were developed. These probes were used to study independently derived SEWA sublines resistant to AMD, VCR, COL, MTX and HU. The results showed that the investigated amplified DNA-segments in AMD-, VCR-. and COL-resistant lines exhibited a high degree of sequence sequence homology, indicating that basically the same segment was amplified in the 3 inductions. In contrast. the amplified DNA-segments in MTX- and HU-resistant lines that do not show the PDR phenotype, displayed no sequence homology to the probes used.

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NATURVETENSKAP  -- Biologi -- Genetik (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Genetics (hsv//eng)

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