ABSTRACT
Most colon cancer cases are initiated by truncating mutations in the tumor suppressor, adenomatous polyposis coli (APC). APC is a critical negative regulator of the Wnt signaling pathway that participates in a multi-protein "destruction complex" to target the key effector protein ß-catenin for ubiquitin-mediated proteolysis. Prior work has established that the poly(ADP-ribose) polymerase (PARP) enzyme Tankyrase (TNKS) antagonizes destruction complex activity by promoting degradation of the scaffold protein Axin, and recent work suggests that TNKS inhibition is a promising cancer therapy. We performed a yeast two-hybrid (Y2H) screen and uncovered TNKS as a putative binding partner of Drosophila APC2, suggesting that TNKS may play multiple roles in destruction complex regulation. We find that TNKS binds a C-terminal RPQPSG motif in Drosophila APC2, and that this motif is conserved in human APC2, but not human APC1. In addition, we find that APC2 can recruit TNKS into the ß-catenin destruction complex, placing the APC2/TNKS interaction at the correct intracellular location to regulate ß-catenin proteolysis. We further show that TNKS directly PARylates both Drosophila Axin and APC2, but that PARylation does not globally regulate APC2 protein levels as it does for Axin. Moreover, TNKS inhibition in colon cancer cells decreases ß-catenin signaling, which we find cannot be explained solely through Axin stabilization. Instead, our findings suggest that TNKS regulates destruction complex activity at the level of both Axin and APC2, providing further mechanistic insight into TNKS inhibition as a potential Wnt pathway cancer therapy.
Subject(s)
Adenosine Diphosphate Ribose/metabolism , Axin Protein/metabolism , Cytoskeletal Proteins/metabolism , Tankyrases/metabolism , beta Catenin/metabolism , Amino Acid Motifs/genetics , Amino Acid Sequence , Animals , Animals, Genetically Modified , Axin Protein/genetics , Blotting, Western , Cell Line, Tumor , Cytoskeletal Proteins/genetics , Drosophila/genetics , Drosophila/metabolism , Drosophila Proteins/genetics , Drosophila Proteins/metabolism , Female , Fluorescent Antibody Technique , HCT116 Cells , Humans , Male , Protein Binding , Substrate Specificity , Tankyrases/genetics , Tumor Suppressor Proteins/genetics , Tumor Suppressor Proteins/metabolism , Two-Hybrid System Techniques , beta Catenin/geneticsABSTRACT
We present a rare case of an abdominal aortic aneurysm (AAA) infected with Campylobacter fetus. The patient presented with abdominal pain and leukocytosis, without a palpable AAA. Computed tomography (CT) of the abdomen showed a 3.1 x 3.0 cm infrarenal abdominal aneurysm with an extra-aortic fluid collection. At surgery, an in situ graft was placed. Intraoperative aortic wall cultures grew pansensitive C. fetus, and blood cultures remained negative. At 9-month follow-up, the patient was doing well without complaints. To our knowledge, this represents only the ninth reported case of an AAA with an aortic wall culture positive for C. fetus.