The tumour-suppressive function of CLU is explained by its localisation and interaction with HSP60

The product of the CLU gene promotes or inhibits tumourigenesis in a context-dependent manner. It has been hypothesised that different CLU isoforms have different and even opposing biological functions, but this theory has not been experimentally validated. Here we show that molecules involved in survival pathways are differentially modulated by the intracellular or secreted forms of CLU. Secreted CLU, which is selectively increased after transformation, activates the survival factor AKT, whereas intracellular CLU inhibits the activity of the oncogenic transcription factor nuclear factor kappa B. Furthermore, intracellular CLU is inactivated by the pro-proliferative and pro-survival activity of the chaperone protein HSP60 in neuroblastoma cells by forming a physical complex. Thus, localisation is key for CLU physiology, explaining the wide range of effects in cell survival and transformation.