Bag3, a nucleotide exchange factor of the heat shock protein Hsp70, has been implicated in cell signaling. Here we report that Bag3 interacts with the SH3 domain of Src, thereby mediating the effects of Hsp70 on Src signaling. Using several complementary approaches, we established that the Hsp70-Bag3 module is a broad-acting regulator of cancer cell signaling, including by modulating the activity of the transcription factors NF-kB, FoxM1 and Hif1α, the translation regulator HuR and the cell cycle regulators p21 and survivin. We also identified a small molecule inhibitor, YM-1, that disrupts Hsp70-Bag3 interaction. YM-1 mirrored the effects of Hsp70 depletion on these signaling pathways, and in vivo administration of this drug was sufficient to suppress tumor growth in mice. Overall, our results defined Bag3 as a critical factor in Hsp70-modulated signaling and offered a preclinical proof-of-concept that the Hsp70-Bag3 complex may offer an appealing anti-cancer target.

Polyglutamine (polyQ) disorders, including Huntington's disease (HD), are caused by expansion of polyQ-encoding repeats within otherwise unrelated gene products. In polyQ diseases, the pathology and death of affected neurons are associated with the accumulation of mutant proteins in insoluble aggregates. Several studies implicate polyQ-dependent aggregation as a cause of neurodegeneration in HD, suggesting that inhibition of neuronal polyQ aggregation may be therapeutic in HD patients. We have used a yeast-based high-throughput screening assay to identify small-molecule inhibitors of polyQ aggregation. We validated the effects of four hit compounds in mammalian cell-based models of HD, optimized compound structures for potency, and then tested them in vitro in cultured brain slices from HD transgenic mice. These efforts identified a potent compound (IC 50 ‫؍‬ 10 nM) with long-term inhibitory effects on polyQ aggregation in HD neurons. Testing of this compound in a Drosophila HD model showed that it suppresses neurodegeneration in vivo, strongly suggesting an essential role for polyQ aggregation in HD pathology. The aggregation inhibitors identified in this screen represent four primary chemical scaffolds and are strong lead compounds for the development of therapeutics for human polyQ diseases.high-throughput screen ͉ small-molecule therapeutics ͉ Drosophila ͉ R6͞2 brain slices ͉ genetic disease A t least nine inherited neurodegenerative diseases, including Huntington's disease (HD), are caused by expansion of polyglutamine (polyQ)-encoding repeats within otherwise unrelated proteins (1, 2). In HD, expansion of polyQ repeats within the huntingtin (Htt) protein causes an adult-onset neurodegenerative disease characterized by movement disorder, psychiatric symptoms, and cognitive dysfunction (3-5). As in several major neurological disorders, including Alzheimer's and Parkinson's diseases, the pathology and death of affected neurons in polyQ diseases are associated with accumulation of mutant polypeptides in insoluble aggregates (6-9). These polyQ-containing aggregates, or inclusions, have been found in the nuclei of affected neurons in postmortem patient tissues and brains from HD transgenic mice (10-12) and have emerged as a hallmark of HD pathology.Mutant polypeptides with extended polyQ tracts aggregate in vitro and in vivo in a polyQ length-dependent manner, which closely correlates with the age of onset in HD and other polyQ-expansion diseases (2,(13)(14)(15). Although the precise role of neuronal aggregates in disease pathogenesis is not clear, therapeutic strategies aimed at inhibiting polyQ aggregation have shown some efficacy in vivo in both Drosophila and mouse models of HD (16,17). These and other studies (18, 19) implicate polyQ-dependent aggregation as a cause of neurodegeneration in HD and suggest that inhibition of neuronal polyQ aggregation may be therapeutic in HD patients (8).Chemical compounds that directly target polyQ aggregation have been identified in high-throughput screens using cell-free ...