Antiproliferative Factor‐Induced Changes in Phosphorylation and Palmitoylation of Cytoskeleton Associated Protein‐4 Regulate its Nuclear Translocation and DNA Binding

Cytoskeleton‐associated protein 4 (CKAP4) is a reversibly palmitoylated and phosphorylated transmembrane protein that links the endoplasmic reticulum and cytoskeleton; it also functions as a high‐affinity receptor for antiproliferative factor (APF)—a sialoglycopeptide secreted from bladder epithelial cells of patients with interstitial cystitis. Previously, we showed that palmitoylation of CKAP4 by the palmitoyl acyltransferase, DHHC2, is required for its cell surface localization, thereby regulating its ability to mediate APF signaling. Others have demonstrated that phosphorylation of three serine residues near the N‐terminus of CKAP4 regulates its association with microtubules. In this study, we investigated the effects of phosphorylation and palmitoylation on the subcellular distribution and function of CKAP4 in response to APF. Our results show that phosphorylation and depalmitoylation of CKAP4 regulate its nuclear translocation following APF binding. We also show that a phosphomimicking, constitutively non‐palmitoylated mutant form of CKAP4 localizes to the nucleus, binds directly to DNA, and mimics the inhibitory effects of APF on cellular proliferation in HeLa cells. These results reveal an unexpected but significant role for CKAP4 in ligand‐dependent signaling from the plasma membrane to the nucleus and suggest that CKAP4 may regulate transcription by binding directly to DNA.