College of Osteopathic Medicine Faculty Articles

PubMed Identifier

2471066

Title

Differential activation of the hprt gene on the inactive X chromosome in primary and transformed Chinese hamster cells.

ISBN or ISSN

1569-2558

Publication Title

Molecular and cellular biology

Volume

9

Issue

4

Publication Date / Copyright Date

4-1-1989

First Page

1635

Last Page

1641

Publisher

American Society for Microbiology

Abstract

We have investigated the genetic activation of the hprt (hypoxanthine-guanine phosphoribosyltransferase) gene located on the inactive X chromosome in primary and transformed female diploid Chinese hamster cells after treatment with the DNA methylation inhibitor 5-azacytidine (5azaCR). Mutants deficient in HPRT were first selected by growth in 6-thioguanine from two primary fibroblast cell lines and from transformed lines derived from them. These HPRT- mutants were then treated with 5azaCR and plated in HAT (hypoxanthine-methotrexate-thymidine) medium to select for cells that had reexpressed the hprt gene on the inactive X chromosome. Contrary to previous results with primary human cells, 5azaCR was effective in activating the hprt gene in primary Chinese hamster fibroblasts at a low but reproducible frequency of 2 x 10(-6) to 7 x 10(-6). In comparison, the frequency in independently derived transformed lines varied from 1 x 10(-5) to 5 x 10(-3), consistently higher than in the nontransformed cells. This increase remained significant when the difference in growth rates between the primary and transformed lines was taken into account. Treatment with 5azaCR was also found to induce transformation in the primary cell lines but at a low frequency of 4 x 10(-7) to 8 x 10(-7), inconsistent with a two-step model of transformation followed by gene activation to explain the derepression of hprt in primary cells. Thus, these results indicate that upon transformation, the hprt gene on the inactive Chinese hamster X chromosome is rendered more susceptible to action by 5azaCR, consistent with a generalized DNA demethylation associated with the transformation event or with an increase in the instability of an underlying primary mechanism of X inactivation.

Disciplines

Medical Specialties | Medicine and Health Sciences | Osteopathic Medicine and Osteopathy

Keywords

Animals, Azacitidine, Cell Line, Cell Transformation, Neoplastic, Cricetinae, Cricetulus, Dosage Compensation, Genetic, Female, Gene Expression Regulation, Hypoxanthine Phosphoribosyltransferase, Mutation, Phenotype, Transcriptional Activation

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