DNA Binding of the Prostate Homeobox Protein NKX3.1

NKX3. 1 is a prostate-specific homeobox gene that maps to chromosome 8p21, a locus frequently deleted in prostate cancer. In the mouse, Nkx3. 1 controls differentiated functions and limits growth of prostate epithelial cells. Although NKX3. 1 may be a tumor suppressor in humans, no cancer specific mutations have been identified in human prostate cancer. Previously, a C-T polymorphism at nucleotide 154 of NKX3.J was identified, resulting in alteration of codon 52 from Arg-Cys in 10-14% of the population. The effects of the NKX3. 1 polymorphism were examined by identifying the consensus DNA binding sites for wild-type (WT) and polymorphic (R52C) NKX3. 1. Binding specificity was confirmed by gel mobility shift. Both WT and R52C NKX3. 1 specifically repressed transcription from a reporter gene downstream from multiple copies of the NKX3. 1 binding site. Amino acid 52 is adjacent to a putative PKC phosphorylation site at serine 48 of NKX3. 1. in vivo analysis of NKX3. 1 indicated that the protein is phosphorylated at serine. in vivo and in vitro phosphorylation studies indicated that R52C NKX3.1 phosphorylation was reduced relative to WT NKX3. 1. Phosphorylation of WT NKX3. 1 resulted in decreased DNA binding affinity, while R52C NKX3. 1 binding affinity appeared unaltered, presumably due to repressed phosphorylation of the mutant protein. The data suggested that polymorphism at position 52 may alter kinase regulation of NKX3. 1.