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Molecular and Cellular Biology, October 1999, p. 6963-6971, Vol. 19, No. 10
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Altered Telomere Nuclear Matrix Interactions and Nucleosomal Periodicity in Ataxia Telangiectasia Cells before and after Ionizing Radiation Treatment

Lubomir B. Smilenov, Sonu Dhar, and Tej K. Pandita*

Center for Radiological Research, College of Physicians and Surgeons, Columbia University, New York, New York 10032

Received 4 April 1999/Returned for modification 24 May 1999/Accepted 14 July 1999

Cells derived from ataxia telangiectasia (A-T) patients show a prominent defect at chromosome ends in the form of chromosome end-to-end associations, also known as telomeric associations, seen at G1, G2, and metaphase. Recently, we have shown that the ATM gene product, which is defective in the cancer-prone disorder A-T, influences chromosome end associations and telomere length. A possible hypothesis explaining these results is that the defective telomere metabolism in A-T cells are due to altered interactions between the telomeres and the nuclear matrix. We examined these interactions in nuclear matrix halos before and after radiation treatment. A difference was observed in the ratio of soluble versus matrix-associated telomeric DNA between cells derived from A-T and normal individuals. Ionizing radiation treatment affected the ratio of soluble versus matrix-associated telomeric DNA only in the A-T cells. To test the hypothesis that the ATM gene product is involved in interactions between telomeres and the nuclear matrix, we examined such interactions in human cells expressing either a dominant-negative effect or complementation of the ATM gene. The phenotype of RKO colorectal tumor cells expressing ATM fragments containing a leucine zipper motif mimics the altered interactions of telomere and nuclear matrix similar to that of A-T cells. A-T fibroblasts transfected with wild-type ATM gene had corrected telomere-nuclear matrix interactions. Further, we found that A-T cells had different micrococcal nuclease digestion patterns compared to normal cells before and after irradiation, indicating differences in nucleosomal periodicity in telomeres. These results suggest that the ATM gene influences the interactions between telomeres and the nuclear matrix, and alterations in telomere chromatin could be at least partly responsible for the pleiotropic phenotypes of the ATM gene.

* Corresponding author. Mailing address: Center for Radiological Research, College of Physicians & Surgeons, Columbia University, VC11-213, 630 West 168th St., New York, NY 10032. Phone: (212) 305-3911. Fax: (212) 305-3229. E-mail: tkp1{at}columbia.edu.

Molecular and Cellular Biology, October 1999, p. 6963-6971, Vol. 19, No. 10
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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