can the same site of repression be site of enhancement?

Well,
I remember me doing my masters project in the non coding regions of mRNA. It started like this.
I want to see the length of the poly AA region in 3'UTRs of an mRNA of a certain hox gene in drosophila. These hox genes are very tricky because they themself being transcription factors, regulate their own expression by inhibiting and being inhibited by their family members itself during patterning the embryo. Can also called name giving genes as they define the regions being expressed. They are also regulated by non coding RNA s as well . Hmm!! very complex :(
To make it even complex :
I was doing my project in the direction of these regions (poly A tails) being used for down regulation of mRNA to be translated.
When I was listening to Prof Simon Morley, University of Sussex Talk about 3'UTR being used for  up regulation as well, I was wondering what makes the site doing two contractory functions.

One possibility being different protein binding action leading to different function. Is there any other hypothesis?