Human telomeric position effect is determined by chromosomal context and telomeric chromatin integrity.
We investigated the influence of telomere proximity and composition on the expression of an EGFP reporter gene in human cells. In transient transfection assays, telomeric DNA does not repress EGFP but rather slightly increases its expression. In contrast, in stable cell lines, the same reporter construct is repressed when inserted at a subtelomeric location. The telomeric repression is transiently alleviated by increasing the dosage of the TTAGGG repeat factor 1 (TRF1). Upon a prolongated treatment with trichostatin A, the derepression of the subtelomeric reporter gene correlates with the delocalization of HP1alpha and HP1beta. In contrast, treating the cells with 5 azacytidin, a demethylating agent, or with sirtinol, an inhibitor of the Sir2 family of deacetylase, has no apparent effect on telomeric repression. Overall, position effects at human chromosome ends are dependent on a specific higher-order organization of the telomeric chromatin. The possible involvement of HP1 isoforms is discussed.
Koering
Catherine Elaine
CE
Laboratoire de Biologie Moléculaire et Cellulaire, UMR5665, Centre National de la Recherche Scientifique, Ecole Normale Supérieure de Lyon, 46 Allée d'Italie, 69364 Lyon cedex 07, France.
Pollice
Alessandra
A
Zibella
Maria Pia
MP
Bauwens
Serge
S
Puisieux
Alain
A
Brunori
Michele
M
Brun
Christine
C
Martins
Luis
L
Sabatier
Laure
L
Pulitzer
John F
JF
Gilson
Eric
E
D002843:Chromatin / Q000378:metabolism*; D000090266:Chromobox Protein Homolog 5; D002877:Chromosomes, Human / Q000378:metabolism*; D005786:Gene Expression Regulation; D020868:Gene Silencing; D017930:Genes, Reporter; D006801:Humans; D016615:Telomere / Q000378:metabolism*; D035321:Telomeric Repeat Binding Protein 1 / Q000235:genetics / Q000378:metabolism; D014407:Tumor Cells, Cultured
C000715593:CBX1 protein, human; C000715594:CBX5 protein, human; D002843:Chromatin; D035321:Telomeric Repeat Binding Protein 1; D000090266:Chromobox Protein Homolog 5