MEK guards proteome stability and inhibits tumor-suppressive amyloidogenesis via HSF1.

Signaling through RAS/MAP kinase pathway is central to biology. ERK has long been perceived as the only substrate for MEK. Here, we report that HSF1, the master regulator of the proteotoxic stress response, is a new MEK substrate. Beyond mediating cell-environment interactions, the MEK-HSF1 regulation impacts malignancy. In tumor cells, MEK blockade inactivates HSF1 and thereby provokes proteomic chaos, presented as protein destabilization, aggregation, and, strikingly, amyloidogenesis. Unlike their non-transformed counterparts, tumor cells are particularly susceptible to proteomic perturbation and amyloid induction. Amyloidogenesis is tumor suppressive, reducing in vivo melanoma growth and contributing to the potent anti-neoplastic effects of proteotoxic stressors. Our findings unveil a key biological function of the oncogenic RAS-MEK signaling in guarding proteostasis and suppressing amyloidogenesis. Thus, proteomic instability is an intrinsic feature of malignant state, and disrupting the fragile tumor proteostasis to promote amyloidogenesis may be a feasible therapeutic strategy.

Widespread genomic breaks generated by activation-induced cytidine deaminase are prevented by homologous recombination.

Activation-induced cytidine deaminase (AID) is required for somatic hypermutation and immunoglobulin class switching in activated B cells. Because AID has no known target-site specificity, there have been efforts to identify non-immunoglobulin AID targets. We show here that AID acts promiscuously, generating widespread DNA double-strand breaks (DSBs), genomic instability and cytotoxicity in B cells with less homologous recombination ability. We demonstrate that the homologous-recombination factor XRCC2 suppressed AID-induced off-target DSBs, promoting B cell survival. Finally, we suggest that aberrations that affect human chromosome 7q36, including XRCC2, correlate with genomic instability in B cell cancers. Our findings demonstrate that AID has promiscuous genomic DSB-inducing activity, identify homologous recombination as a safeguard against off-target AID action, and have implications for genomic instability in B cell cancers.

Hydrogen bond serving as a protecting group to enable the photocatalytic [2+2] cycloaddition of redox-active aliphatic-amine-containing indole derivatives.

Redox-sensitive functionalities such as aliphatic amines with low oxidation potentials and easily oxidized by photocatalysts are generally not compatible with photocatalytic reactions. We describe a hydrogen-bond-assisted visible-light-mediated [2+2] cycloaddition of redox-sensitive aliphatic-amine-containing indole derivatives providing a range of cyclobutane-fused polycyclic indoline derivatives, especially bridged-cyclic indolines. Mechanistic studies indicated that the success of the reaction was based on on the formation of H-bonds between the N-atom and alcohol proton of TFE or HFIP, with this formation preventing or blocking the single-electron transfer from the aliphatic amine functionality to the excited photocatalyst.

Cancer cell-nanomaterial interface: role of geometry and surface charge of nanocomposites in the capture efficiency and cell viability.

The nanomaterial-cell interface plays an important role in biodetection and therapy. Several parameters involved in the bio-nano interaction such as size, shape, surface charge, surface functionality and protein corona on the nanomaterials have been studied. Recently, we found that the surface charge of the cancer cell membrane derived from the glycolysis could be a general hallmark for cancer cell targeting and very efficient isolation by tailored nanoparticles. However, to simultaneously achieve high capture efficiency and optimal cell viability, the influence of critical features of nanomaterials, such as surface charge and geometry, must be explored. In this study, we designed and synthesized spherical core-shell magnetic particles and Fe3O4 particle coated graphene oxide nanosheets with a similar surface chemistry, charge and magnetization, but different geometries. Although the two-dimensional (2D) graphene oxide based nanocomposites possessed higher capture efficiency at a low working concentration as compared to the spherical nanocomposites, they also exhibited more obvious cytotoxicity. Different aspects of the mechanism underlying the higher cytotoxicity from the 2D nanomaterials were investigated. The results of this study can guide the design of versatile candidates for the isolation of cancer cells.

Enhancement of membrane stability on magnetic responsive hydrogel microcapsules for potential on-demand cell separation.

It is of high interest to obtain hydrogel membranes with optimum mechanical stability, which is a prerequisite to the successful fabrication of hydrogel microcapsules for cell separation. In this work, we developed magnetic responsive alginate/chitosan (MAC) hydrogel microcapsules by co-encapsulation of microbial cells and superparamagnetic iron oxide nanoparticles (SPIONs) reacting under a high voltage electrostatic field. We investigated the influence of the molecular weight of chitosan, microcapsules size, and membrane crosslinking time on the swelling behavior of microcapsules as an indicator of stability of the membranes. The results demonstrated that the suitable membrane stability conditions were obtained by a crosslinking of the microspheres with a chitosan presenting a molecular weight of 70kDa for 15-30min resulting in a membrane thickness of approximately 30mm. Considering the need of maintaining the cells inside the microcapsules, fermentation at 37°C and at neutral pH was favorable. Moreover, the MAC microcapsules sizing between 300 and 380µm were suitable for immobilizing Bacillus licheniformis in a 286h multiple fed-bath operation with no leakage of the SPIONs and cells. Overall, the results of this study provided strategies for the rational design of magnetic microcapsules exhibiting suitable mechanical stable membranes.

HSF1 critically attunes proteotoxic stress sensing by mTORC1 to combat stress and promote growth.

To cope with proteotoxic stress, cells attenuate protein synthesis. However, the precise mechanisms underlying this fundamental adaptation remain poorly defined. Here we report that mTORC1 acts as an immediate cellular sensor of proteotoxic stress. Surprisingly, the multifaceted stress-responsive kinase JNK constitutively associates with mTORC1 under normal growth conditions. On activation by proteotoxic stress, JNK phosphorylates both RAPTOR at S863 and mTOR at S567, causing partial disintegration of mTORC1 and subsequent translation inhibition. Importantly, HSF1, the central player in the proteotoxic stress response (PSR), preserves mTORC1 integrity and function by inactivating JNK, independently of its canonical transcriptional action. Thereby, HSF1 translationally augments the PSR. Beyond promoting stress resistance, this intricate HSF1-JNK-mTORC1 interplay, strikingly, regulates cell, organ and body sizes. Thus, these results illuminate a unifying mechanism that controls stress adaptation and growth.