INVESTIGADORES
GUBERMAN Alejandra Sonia
artículos
Título:
Inhibitory effect of AP-1 complex on 5-Aminolevulinate Synthase gene expression through sequestration of CBP coactivator
Autor/es:
GUBERMAN, A. S., SCASSA, M. E., GIONO, L., VARONE, C., CÁNEPA, E. T.
Revista:
JOURNAL OF BIOLOGICAL CHEMISTRY
Referencias:
Año: 2003 vol. 278 p. 2317 - 2326
ISSN:
0021-9258
Resumen:
Activation protein-1
(AP-1) transcription factors are early response genes involved in a
diverse set of transcriptional regulatory processes. The phorbol ester
12-O-tetradecanoylphorbol-13-acetate (TPA) is often used to
induce AP-1 activity. The purpose of this work was to explore the
molecular mechanisms involved in the TPA regulation of ubiquitous
5-aminolevulinate synthase (ALAS) gene expression, the first and
rate-controlling step of the heme biosynthesis. Previous analysis of
the 5'-flanking sequence of ALAS revealed the existence of two
cAMP-response elements (CRE) required for basal and cAMP-stimulated
expression. The fragment 833 to +42 in the 5'-flanking region of rat
ALAS gene was subcloned into a chloramphenicol acetyltransferase (CAT)
reporter vector. The expression vector pALAS/CAT produced a significant
CAT activity in transiently transfected HepG2 human hepatoma cells,
which was repressed by TPA. Sequence and deletion analysis detected a
TPA response element (TRE), located between 261 and 255 (TRE-ALAS), that was critical for TPA regulation. We demonstrated that c-Fos, c-Jun, and JunD are involved in TPA inhibitory effect due to their ability to bind TRE-ALAS, evidenced by supershift analysis and their
capacity to repress promoter activity in transfection assays. Repression of ALAS promoter activity by TPA treatment or Fos/Jun overexpression was largely relieved when CRE protein-binding protein or
p300 was ectopically expressed. When the TRE site was placed in a
different context with respect to CRE sites, it appeared to act as a
transcriptional enhancer. We propose that the decrease in ALAS basal
activity observed in the presence of TPA may reflect a lower ability of
this promoter to assemble the productive pre-initiation complex due to
CRE protein-binding protein sequestration. We also suggest that the
transcriptional properties of this AP-1 site would depend on a
spatial-disposition-dependent manner with respect to the
CRE sites and to the transcription initiation site.