No abstract

Although targeted therapies often elicit profound initial patient responses, these effects are transient due to residual disease leading to acquired resistance. How tumors transition between drug responsiveness, tolerance and resistance, especially in the absence of pre-existing subclones, remains unclear. In EGFR-mutant lung adenocarcinoma cells, we demonstrate that residual disease and acquired resistance in response to EGFR inhibitors requires AURKA activity. Non-genetic resistance through the activation of AURKA by its co-activator TPX2 emerges in response to chronic EGFR inhibition where it mitigates drug-induced apoptosis. Aurora kinase inhibitors suppress this adaptive survival program, increasing the magnitude and duration of EGFR inhibitor response in pre-clinical models. Treatment induced activation of AURKA was associated with resistance to EGFR inhibitors in-vitro, in-vivo and in individuals with EGFR-mutant lung adenocarcinoma. These findings delineate a path whereby drug resistance emerges from drug-tolerant cells and unveils a synthetic lethal strategy for enhancing responses to EGFR inhibitors by suppressing AURKA driven residual disease and acquired resistance.

The small heat shock protein αB-crystallin is an oligomeric molecular chaperone that binds aggregation-prone proteins. As a component of the proteostasis system, it is associated with cataract, neurodegenerative diseases, and myopathies. The structural determinants for the regulation of its chaperone function are still largely elusive. Combining different experimental approaches, we show that phosphorylation-induced destabilization of intersubunit interactions mediated by the N-terminal domain (NTD) results in the remodeling of the oligomer ensemble with an increase in smaller, activated species, predominantly 12-mers and 6-mers. Their 3D structures determined by cryo-electron microscopy and biochemical analyses reveal that the NTD in these species gains flexibility and solvent accessibility. These modulated properties are accompanied by an increase in chaperone activity in vivo and in vitro and a more efficient cooperation with the heat shock protein 70 system in client folding. Thus, the modulation of the structural flexibility of the NTD, as described here for phosphorylation, appears to regulate the chaperone activity of αB-crystallin rendering the NTD a conformational sensor for nonnative proteins.olecular chaperones share the ability to bind nonnative, aggregation-prone polypeptides and assist their folding and assembly (1-3). Among these, the small heat shock protein (sHsp) αB-crystallin (also HspB5) is one of the major constituents of the vertebrate eye lens where it functions both as a chaperone and structural protein (4, 5). In nonlenticular tissues, αB-crystallin (αB) participates in sustaining cellular proteostasis. The involvement in neurodegenerative diseases (6, 7), multiple sclerosis (8), myopathies (9), as well as in cell cycle control, apoptosis, and cancer (10, 11) underlines its importance for cellular proteostasis.αB exhibits a tripartite organization (Fig. 1A) with a central α-crystallin domain (ACD) flanked by an N-terminal domain (NTD) and a short C-terminal extension (CTE) (12, 13). The ACD forms stable dimers (14-16) that further assemble into higher-order oligomers via interactions mediated by the NTD and CTE (17)(18)(19). αB forms dynamic populations of multimers with a variable number of subunits (20,21). Structural studies indicate that the variety of oligomeric states including a symmetric 24-mer (22) is created by addition of subunits to (or subtraction from) existing oligomers (17, 18). As for many other sHsps (23), the polydispersity of αB is coupled to spontaneous subunit exchange of yet undetermined units. αB quaternary dynamics was attributed to fluctuations of the intersubunit contacts mediated by the C-terminal IXI motif (24). However, given its involvement in oligomer formation, the NTD must also play a decisive role.In general, sHsps including αB recognize aggregation-prone, partially unfolded substrates (4, 25, 26) and keep them in a refolding-competent state (27, 28). The substrate binding sites of sHsps have not been defined yet. Recent studies suggest the involvement ...