Abstract 2566: Blocking the functional domain of TIP1 upregulates midkine via the β-catenin/Wnt signaling pathway

Abstract

Abstract Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related mortalities world-wide. Targeted therapy has been a growing topic of investigation to improve therapeutic efficacy for NSCLC. A few targeted therapies that exploit aberrant protein expression profiles have been approved for NSCLC. However, marginal improvement in efficacy observed with these therapeutic approaches highlights the need for discovery of additional therapeutic targets. Tax interacting protein 1 (TIP1) is a molecular target that is overexpressed on the surface of various cancers and correlates with poor overall patient survival. The functional domain of TIP1 (PDZ domain) caps the C-terminus of many cellular proteins that regulate cell signaling, cancer development, and progression. We found that antibodies against the PDZ domain of TIP1 induced cytotoxicity of lung cancer cells but not normal cells. A quantitative mass spectrometry-based approach identified a ten-fold increase in Midkine protein expression on blockade of TIP1. Midkine is a heparin-binding growth factor that is involved in cancer progression, therapy resistance, and immune suppression. This study tested the hypothesis that Midkine is upregulated by the anti-PDZ/TIP1 antibody via the β-catenin/Wnt signaling pathway, which subsequently modulates downstream signaling mechanisms. In co-immunoprecipitation studies we found a direct interaction of TIP1 with β-catenin on the cell surface. Anti-TIP1 antibody treatment led to nuclear translocation of β-catenin in NSCLC cells. We used a luciferase based TOPFlash/FOPFlash reporter assay to study the transcriptional activity of the canonical β-catenin/Wnt pathway following TIP1 blockade. Reporter assays showed a three to four-fold increase (p<0.0001) in the transcriptional activity of β-catenin following TIP1 blockade in NSCLC cells. Genetic silencing of β-catenin inhibited Midkine mRNA transcription (p<0.005), protein induction and its extracellular release (p<0.0001) following anti-TIP1 antibody treatment. In conclusion, the mechanism of Midkine release following TIP1 blockade involves the β-catenin/Wnt signaling pathway. Ongoing studies are evaluating the dual-targeting of TIP1 and Midkine for enhanced efficacy of NSCLC treatment. Citation Format: Minakshi Saikia, Abhay K. Singh, Nathan Cheung, Dennis E. Hallahan, Vaishali Kapoor. Blocking the functional domain of TIP1 upregulates midkine via the β-catenin/Wnt signaling pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2566.