The Journal of Neuroscience, April 1, 2002, 22(7):2579-2589
A Proximal Promoter Domain Containing a Homeodomain-Binding Core
Motif Interacts with Multiple Transcription Factors, Including HoxA5
and Phox2 Proteins, and Critically Regulates Cell Type-Specific
Transcription of the Human Norepinephrine Transporter Gene
Chun-Hyung
Kim,
Dong-Youn
Hwang,
Jae-Joon
Park, and
Kwang-Soo
Kim
Molecular Neurobiology Laboratory, McLean Hospital, Harvard Medical
School, Belmont, Massachusetts 02478
Expression of the norepinephrine transporter (NET), which mediates
the reuptake of norepinephrine into presynaptic nerve terminals, is
restricted to noradrenergic (NA) neurons. We have demonstrated previously that the 9.0 kb upstream sequences and the first intron residing in the 5' untranslated area are critical for high-level and NA
cell-specific transcription. Here, using transient transfection assays,
we show that 4.0 kb of the 5' upstream sequences contains sufficient
genetic information to drive reporter gene expression in an NA cell
type-specific manner. Three functional domains appear to be potentially
important for the regulation of human NET
(hNET) gene transcription: an upstream enhancer
region at
4.0 to
3.1 kb, a proximal domain at
133 to
75 bp, and
a middle silencer region between these two domains. DNase I
footprinting analysis of the proximal promoter region shows that a
subdomain at
128 to
80 bp is protected in a cell-specific manner.
We provide evidence that multiple protein factors interact with the
proximal promoter domain to critically regulate the transcriptional
activity of the hNET gene. In the middle of this proximal
subdomain resides a homeodomain (HD)-binding core motif, which
interacts with HD factors, including Phox2a and HoxA5, in an
NA-specific manner. Cotransfection analyses suggest that HoxA5 and
Phox2a may transactivate the hNET gene promoter. Together
with previous studies indicating direct activation of dopamine
-hydroxylase transcription by Phox2a/2b, the present results support
a model whereby Phox2 proteins may coordinately regulate the phenotypic
specification of NA neurons by activating both NA biosynthetic and
reuptake genes.
Key words:
norepinephrine transporter; promoter; noradrenergic
neuron; cell type-specific transcription; cis-acting
element; homeodomain; Phox2a; HoxA5
Copyright © 2002 Society for Neuroscience 0270-6474/02/2272579-11$05.00/0