Investigating The Role Of RBM4 In Expression Of ULBP-1, A NKG2D Ligand

NKG2D is an activating immune receptor found on natural killer cells, and some T-cell subsets, which binds to a family of cell surface proteins.  Stressed, transformed or virally infected cells, such as cancer cells, frequently express NKG2D ligands at high levels, while normal cells show little to no expression of these ligands; therefore, a natural killer cell will destroy an abnormal cell it recognizes via the NKG2D receptor.  In order to further understand the regulation of NKG2D ligand expression, we are studying the human NKG2D ligand ULBP-1.  A genetic screen of a human cell line identified RNA-binding motif protein 4 (RBM4) as a potential regulator of ULBP-1; thus, our goal is to determine if RBM4, and/or RBM4 isoforms that arise as a result of alternative-splicing, are involved in ULBP-1 regulation.  RBM4 is a ubiquitously expressed protein which plays a role in the alternative splicing of pre-mRNA, translation, and RNA silencing.  We hypothesize that increasing RBM4 expression will also increase ULBP-1 expression.  To test this hypothesis, we will over-express RBM4 or its isoforms in 293T cells via transient transfection.  Our second aim is to restore RBM4 expression in a haploid human cell line in which the RBM4 gene was inactivated by insertion of a retroviral gene trap.  In this case, we hypothesize that adding a functional copy of RBM4 will restore ULBP-1 expression.  If we determine that RBM4 regulates ULBP-1, it is possible that RBM4 can serve as a target for cancer therapy drugs.