Structural and Functional Interactions of the Prostate Cancer Suppressor NKX3.1 with Topoisomerase I

NKX3.1 is a prostate tumor suppressor protein that binds to topoisomerase I and enhances its DNA cleavage activity. We show that the NKX3.1 homeodomain binds to a region of topoisomerase I spanning the junction between core and linker domains. NKX3.1 activated N-terminal truncated topoisomerase I (Topo70) in vitro. In contrast, NKX3.1 interacts with the enzyme reconstituted from peptide fragments of core domain and linker-active site domains, but inhibits the DNA unwinding activity of the reconstituted enzyme in vitro. The effect of NKX3.1 on both Topo70 and the reconstituted enzyme was seen in the presence and absence of camptothecin. Neither NKX3.1 nor camptothecin had an effect on the interaction of the other with topoisomerase I. Therefore the interactions of NKX3.1 and camptothecin with the linker domain of topoisomerase I are mutually exclusive. However, in cells the effect of NKX3.1 on topoisomerase binding to DNA sensitized cells to cellular toxicity and induction of apoptosis by low dose CPT. Lastly, topoisomerase I is important for the effect of NKX3.1 on cell survival after DNA damage as topoisomerase knockdown blocked the effect of NKX3.1 on clonogenicity after DNA damage. Therefore, NKX3.1 and topoisomerase I interact in vitro and in cells to affect CPT sensitivity and DNA repair functions of NKX3.1.
Source: BJ Gene - Category: Biochemistry Authors: Tags: BJ Biomolecules Source Type: research