TRANSCRIPTIONAL SUPPRESSION OF THE HUMAN T-CELL LEUKEMIA-VIRUS TYPE-ILONG TERMINAL REPEAT OCCURS BY AN UNCONVENTIONAL INTERACTION OF A CREB FACTOR WITH THE R-REGION
X. Xu et al., TRANSCRIPTIONAL SUPPRESSION OF THE HUMAN T-CELL LEUKEMIA-VIRUS TYPE-ILONG TERMINAL REPEAT OCCURS BY AN UNCONVENTIONAL INTERACTION OF A CREB FACTOR WITH THE R-REGION, Molecular and cellular biology, 14(8), 1994, pp. 5371-5383
To analyze regulation of the human T-cell leukemia virus type I (HTLV-
I) long terminal repeat (LTR), cell lines were generated from LTR-tax
x LTR-beta-galactosidase (beta-Gal) doubly transgenic mouse fibroblast
ic tumors. The HTLV-I LTR directs expression of both the fax and lacZ
genes, and Tax up-modulates both promoters in primary cells. However,
once cells were transformed by tax, beta-Gal but not tax expression wa
s suppressed. Supertransformation of these cells with v-src suppressed
both beta-Gal and tax expression. This suppression was reversed by tr
eatment with the tyrosine kinase inhibitor herbimycin A or protein kin
ase A inhibitor H8. Electrophoretic mobility shift assays demonstrated
augmented binding in the R but not U3 region. This binding was compet
itively inhibited by a high-affinity CREB oligodeoxynucleotide and sup
er-shifted with a specific CREB antibody. Treatment of cells with the
cyclic AMP analog dibutyryl cyclic AMP also transiently increased the
R region binding dramatically. In vitro DNase I footprint analysis ide
ntified a protein-binding sequence in the R region which corresponded
with suppression. However, this target sequence lacked a conventional
CREB-binding site. A 70.5-kDa DNA-binding protein was partially purifi
ed by affinity chromatography, along with a 49-kDa protein which react
ed with CREB-specific sera. These data demonstrate that HTLV-I LTR sup
pression is associated with CREB factor binding in the R region, proba
bly by direct interaction with a 70.5-kDa protein, and provide a novel
mechanism for maintenance of viral latency.