Novel interaction with PSMD9 regulates DNAJA1 turnover and mitochondrial polarity

Understanding protein-protein interactions in cancer is essential for the development of innovative therapeutic strategies. Chaperone proteins often form cooperative networks that regulate key cellular processes, many of which are disrupted in cancer, offering potential targets for intervention. PSMD9, a chaperone involved in 26S proteasome assembly, is frequently overexpressed in various cancers and is linked to resistance to chemotherapy and radiotherapy. It also plays roles in intracellular signaling. Mass spectrometry analysis of proteins co-purified with PSMD9 revealed a subset containing a specific EXKK motif, suggesting potential direct interactions. Among these was DNAJA1, a chaperone involved in mitochondrial protein transport. This study explores and characterizes the interaction between PSMD9 and DNAJA1. The interaction was confirmed through in vitro binding assays using purified proteins and further validated by introducing mutations in DNAJA1 that disrupted the binding. Co-immunoprecipitation from MCF7 breast cancer cells supported the in-cell interaction. Upon proteasomal inhibition, interaction between PSMD9 and DNAJA1 was enhanced in MCF7 cells, correlating with increased DNAJA1 stability. Additionally, PSMD9 depletion led to elevated mitochondrial membrane potential, linking this interaction to mitochondrial regulation. Thus, beyond its known role in cytoplasmic proteostasis, PSMD9 may influence mitochondrial homeostasis via DNAJA1.