Istres
It is in the Provence-Alpes-Côte d'Azur region , in the Bouches-du-Rhône department , of which it is a subprefecture . 
<triplet> Provence-Alpes-Côte d'Azur <subj> region <obj> instance of <subj> Bouches-du-Rhône <obj> contains administrative territorial entity <triplet> Bouches-du-Rhône <subj> Provence-Alpes-Côte d'Azur <obj> located in the administrative territorial entity <subj> department <obj> instance of <triplet> department <subj> region <obj> part of