DAPK3 modulates migration and invasion of triple negative breast cancers

A mass spectrometry (MS)-based kinase inhibitor pulldown assay (KIPA) was applied to analyze 16 patient-derived xenografts (PDXs) leading to the discovery that Death-Associated Protein Kinase 3 (DAPK3) is significantly and specifically overexpressed in triple negative breast cancer (TNBC). Validation studies confirmed the enrichment of DAPK3 at the protein level, independent of RNA expression, in both TNBC cell lines and tumors. Genomic knockout of DAPK3 in TNBC cell lines inhibited in vitro migration and invasion, along with downregulation of an epithelial-mesenchymal transition (EMT) signature. The kinase and leucine-zipper domains within DAPK3 were shown by mutational analysis to be essential for functionality. Notably, DAPK3 was found to inhibit the levels of desmoplakin (DSP), a crucial component of the desmosome complex, thereby explaining TNBC migration and invasion effects. Further exploration with immunoprecipitation-mass spectrometry (IP-MS) identified Leucine-zipper protein 1 (LUZP1) as a strong binding partner of DAPK3, engaging in a leucine-zipper-domain-mediated interaction that protects DAPK3 from degradation. Thus, DAPK3 emerges as a novel regulator of EMT components in TNBC.