Trans-activation of human globin genes by HTLV-I tax1
HB Fox, PD Gutman, HP Dave, SX Cao, M Mittelman, PE Berg and AN Schechter
Laboratory of Chemical Biology, National Institute of Diabetes, Digestive
and Kidney Diseases, Bethesda, MD 20892.
We studied the effects of a known retroviral trans-activating factor,
HTLV-I tax1, on transcription of human globin genes. Transfection of HeLa
cells by the cloned tax1 gene stimulated activity of both the beta- and
epsilon-globin promoters approximately 20-fold, as measured by
chloramphenicol acetyl transferase (CAT) assays. Studies of promoter 5'-
deletion mutants revealed that the trans-activation response required only
185 base pairs (bp) of beta-globin 5'-flanking sequence or 177 bp of
epsilon-globin 5' flanking sequence. These promoter regions contain either
two (for beta) or three (for epsilon) copies of the pentanucleotide
sequence CTGAC, which is characteristic of previously described
tax1-responsive promoters. We also stably transfected tax1 into the
erythroid cell line K562. Transfectants expressing tax1 showed increased
transcription of epsilon-, gamma-, zeta-, and alpha-globins. This indicates
that tax1 can stimulate transcription of globin genes in their native
chromosomal location. This was confirmed by measurements of increases in
intracellular hemoglobin as determined by an increased percentage of cells
staining with benzidine and by spectrophotometric measurements of
hemoglobin. The observed trans-activation of globin genes by tax1 may
provide insight into normal regulation of globin genes by clarifying cis
regulatory sequences. Furthermore, it suggests that the trans-acting
effects of tax1 on heterologous genes are more widespread than was
previously appreciated.
Volume 74,
Issue 8,
pp. 2749-2754,
12/01/1989
Copyright © 1989 by The American Society of Hematology
