Loss of Cytoskeleton‐Associated Protein 4 (CKAP4) Expression Enhances α5β1‐mediated Bladder Cancer Cell Adhesion and Migration

Abstract

The transmembrane protein cytoskeleton‐associated protein 4 (CKAP4) plays an essential role in the maintenance of endoplasmic reticulum structure by anchoring the rough ER to microtubules in epithelial cells. CKAP4 has also been identified as a biologically relevant receptor for four unique ligands—tissue plasminogen activator, surfactant protein A, Dickkopf1, and antiproliferative factor. Recent data indicates that loss of CKAP4 expression leads to remodeling of the actin cytoskeleton, including disruption of actin stress fibers, and altered expression of genes known to promote cell motility and dynamic changes in the cytoskeleton. Among these genes, β1‐integrin expression was dramatically increased in response to CKAP4 silencing. Given the importance of tumor cell adhesion and migration for cancer invasion and metastasis, it is important to understand how CKAP4, through modulation of integrin functions, acts to regulate these cellular processes. To this end, we took a loss‐of‐function approach where CKAP4 expression was knocked down by means of siRNA in the human bladder carcinoma cell line T24. Western blot analysis revealed that CKAP4 knockdown induced β1‐integrin protein levels after 24 hours and continued to increase up to 96 hours after transfection with CKAP4 siRNA. Because β1‐integrin associates with α5‐integrin to form the fibronectin receptor, we investigated whether α5‐integrin protein levels are affected by CKAP4 knockdown. Western blot analysis revealed that CKAP4 knockdown induced α5‐integrin protein levels after 24 hours and continued to increase up to 96 hours after transfection with CKAP4 siRNA. Importantly, loss of CKAP4 led to increased surface expression of β1 and α5 integrin and increased cell adhesion and migration on fibronectin as measured by flow cytometry and electric cell‐substrate impedance sensing, respectively. Activation of ER stress and AMPK signaling pathways was also observed in CKAP4‐silenced bladder carcinoma cells. Our data indicate that CKAP4 knockdown mediates adhesion and migration of human bladder cancer cells through transcriptional up‐regulation of α5β1 integrin.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.