Summary: | Previously data from out lab have shown that BTG2 is up-regulated in both in vitro and
in vivo ischemic models. We hypothesize that BTG2 may play a neuro-protective role
following glutamate-mediated activation of NMDAR, and that this neuro-protection depends
on the collaboration of various transcription factors and cis-acting elements that are found on
the BTG2 promoter.
To determine the function of BTG2 , BTG2 was either over-expressed or reduced in rat
cortical neurons, and treated with either NMDA or oxygen glucose deprivation (OGD).
Over-expression of BTG2 reduced NMDA-induced cell death, as measured by LDH assay,
and reduced activation of Caspase 3. In addition, CyclinDl mRNA level was significantly
increased following NMDA treatment in cells with reduced BTG2 expression by siRNA.
Thus, BTG2 appeared to have a neuro-protective function, possibly through down-regulation
of CyclinDl expression.
To better understand the mechanism that regulated BTG2 expression, we studied the
BTG2 promoter by cloning various lengths of BTG2 promoter into a luciferase expression
vector. The role of two specific cis-acting elements, a putative P53 binding element P53RE
(-53/-94) (-53 to -94 relative to ATG) and a GAGA box, were investigated. While the
isolated P53RE (-537-94) sequence functioned as a cis-activating and NMDA inducible element, it became repressive in the context of BTG2 promoter. Removal of P53RE
(-53A94) and/or GAGA box not only increased the BTG2 promoter activity, but also made
the promoter inducible to NMDA. Consistently, reduction of P53 expression with P53
siRNA led to a significant increase in basal BTG2 expression. Immuno-coprecipitation
results showed that the P53 and the GAGA box binding protein were associated together.
Taken together, our results suggest that P53 may associate with GAGA box binding protein
to form a complex to repress BTG2 expression. A hypothetical mode of action is then
proposed, showing that binding of P53 to the P53RE (-53/-94) may activate GAGA box
caused suppression, which becomes dominant for BTG2 expression. This mode illustrates
a possible mechanism that an transactivating factor P53 and its cis-activating binding site
can be turned into a suppressor depending on the location of P53 binding site and the
transcriptional regulator(s) P53 associated with. === Medicine, Faculty of === Graduate
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