Decay of the Stress-Induced Ligand MICA Is Controlled by the Expression of an Alternative 3' Untranslated Region.

Recognition of the human stress-induced ligand MHC class I polypeptide-related sequence A (MICA) by the receptor NKG2D expressed on NK cells leads to NK cell-mediated killing of the target cells. Hence, the expression of MICA must be tightly regulated, and its cell surface expression needs to be quickly downregulated to avoid inappropriate activation of immune cells. In this article, we describe a transcript variant of human MICA that has not yet been studied, which contains a 3' untranslated region of 119 nt instead of 174. We identify its polyadenylation signal and demonstrate that, upon stresses, such as heat shock, butyrate treatment, and some oxidative and DNA-damaging treatments, the balance between the two MICA variants changes in favor of the less stable, longer variant. Mechanistically, we showed that this change is linked to microRNA activity and that poly-ADP ribose polymerase 1 is involved in the induction of the longer variant following stress. Thus, to our knowledge, we identify the first regulatory mechanism of a stress ligand's decay and also provide one of the first physiological examples for the biological function of a longer 3' untranslated region of a particular gene.