Silica-coated LiYF4:Yb3+, Tm3+ upconverting nanoparticles are non-toxic and activate minor stress responses in mammalian cells.

Lanthanide-doped upconverting nanoparticles (UCNPs) are ideal candidates for use in biomedicine. The interaction of nanomaterials with biological systems determines whether they are suitable for use in living cells. In-depth knowledge of the nano-bio interactions is therefore a pre-requisite for the development of biomedical applications. The current study evaluates fundamental aspects of the NP-cell interface for square bipyramidal UCNPs containing a LiYF4:Yb3+, Tm3+ core and two different silica surface coatings. Given their importance for mammalian physiology, fibroblast and renal proximal tubule epithelial cells were selected as cellular model systems. We have assessed the toxicity of the UCNPs and measured their impact on the homeostasis of living non-malignant cells. Rigorous analyses were conducted to identify possible toxic and sub-lethal effects of the UCNPs. To this end, we examined biomarkers that reveal if UCNPs induce cell killing or stress. Quantitative measurements demonstrate that short-term exposure to the UCNPs had no profound effects on cell viability, cell size or morphology. Indicators of oxidative, endoplasmic reticulum, or nucleolar stress, and the production of molecular chaperones varied with the surface modification of the UCNPs and the cell type analyzed. These differences emphasize the importance of evaluating cells of diverse origin that are relevant to the intended use of the nanomaterials. Taken together, we established that short-term, our square bipyramidal UCNPs are not toxic to non-malignant fibroblast and proximal renal epithelial cells. Compared with established inducers of cellular stress, these UCNPs have minor effects on cellular homeostasis. Our results build the foundation to explore square bipyramidal UCNPs for future in vivo applications.

Oxidative stress and signaling through EGFR and PKA pathways converge on the nuclear transport factor RanBP1.

Nuclear protein trafficking requires the soluble transport factor RanBP1. The subcellular distribution of RanBP1 is dynamic, as the protein shuttles between the nucleus and cytoplasm. To date, the signaling pathways regulating RanBP1 subcellular localization are poorly understood. During interphase, RanBP1 resides mostly in the cytoplasm. We show here that oxidative stress concentrates RanBP1 in the nucleus, and our study defines the underlying mechanisms. Specifically, RanBP1's cysteine residues are not essential for its oxidant-induced relocation. Furthermore, our pharmacological approaches uncover that signaling mediated by epidermal growth factor receptor (EGFR) and protein kinase A (PKA) control RanBP1 localization during stress. In particular, pharmacological inhibitors of EGFR or PKA diminish the oxidant-dependent relocation of RanBP1. Mutant analysis identified serine 60 and tyrosine 103 as regulators of RanBP1 nuclear accumulation during oxidant exposure. Taken together, our results define RanBP1 as a target of oxidative stress and a downstream effector of EGFR and PKA signaling routes. This positions RanBP1 at the intersection of important cellular signaling circuits.

Valosin containing protein (VCP): initiator, modifier, and potential drug target for neurodegenerative diseases.

The AAA+ ATPase valosin containing protein (VCP) is essential for cell and organ homeostasis, especially in cells of the nervous system. As part of a large network, VCP collaborates with many cofactors to ensure proteostasis under normal, stress, and disease conditions. A large number of mutations have revealed the importance of VCP for human health. In particular, VCP facilitates the dismantling of protein aggregates and the removal of dysfunctional organelles. These are critical events to prevent malfunction of the brain and other parts of the nervous system. In line with this idea, VCP mutants are linked to the onset and progression of neurodegeneration and other diseases. The intricate molecular mechanisms that connect VCP mutations to distinct brain pathologies continue to be uncovered. Emerging evidence supports the model that VCP controls cellular functions on multiple levels and in a cell type specific fashion. Accordingly, VCP mutants derail cellular homeostasis through several mechanisms that can instigate disease. Our review focuses on the association between VCP malfunction and neurodegeneration. We discuss the latest insights in the field, emphasize open questions, and speculate on the potential of VCP as a drug target for some of the most devastating forms of neurodegeneration.

Multiple pathways promote microtubule stabilization in senescent intestinal epithelial cells.

Intestinal epithelial cells are critical for gastrointestinal homeostasis. However, their function declines during aging. The aging-related loss of organ performance is largely driven by the increase in senescent cells. To date, the hallmarks and molecular mechanisms related to cellular senescence are not fully understood. Microtubules control epithelial functions, and we identified microtubule stabilization as a phenotypic marker of senescent intestinal epithelial cells. The senescence inducer determined the pathway to microtubule stabilization. Specifically, enhanced microtubule stability was associated with α-tubulin hyperacetylation or increased abundance of the microtubule-binding protein tau. We show further that overexpression of MAPT, which encodes tau, augmented microtubule stability in intestinal epithelial cells. Notably, pharmacological microtubule stabilization was sufficient to induce cellular senescence. Taken together, this study provides new insights into the molecular mechanisms that control epithelial cell homeostasis. Our results support the concept that microtubule stability serves as a critical cue to trigger intestinal epithelial cell senescence.

A lacZ reporter with high activity in the human fungal pathogen Candida albicans.

Reporter genes are useful tools to study gene transcription in various organisms. For example, the lacZ gene encoding ß-galactosidase has been extensively used as a reporter in bacteria, budding yeast, fruit fly, mouse etc. However, use of this gene in the human fungal pathogen Candida albicans has been limited, probably due to low ß-galactosidase activity. Here, we describe a reporter derived from the Vibrio cholerae lacZ gene in which codons have been optimized for expression in C. albicans. The constitutively active ACT1 promoter was fused to this synthetic lacZ reporter and integrated in the C. albicans genome. High ß-galactosidase activity in liquid assays was observed for this reporter as well as coloration on X-gal plates. When the lacZ reporter expression was driven by the MET3 promoter, ß-galactosidase activity in liquid assays and coloration on X-gal plates was higher in the absence of methionine, thus recapitulating the regulation of the native MET3 gene. This synthetic lacZ gene extends the toolbox of C. albicans reagents by providing a useful reporter for analysis of promoter activity in this organism of medical importance.

Exploring near-infrared absorbing nanocarriers to overcome cancer drug resistance.

One of the major obstacles of successful cancer therapy is cancer drug resistance. The unique tools and applications developed by nanomedicine provide new approaches to surmount this common limitation of current treatment regimens. Nanocarriers that absorb light in the near-infrared spectrum are particularly suitable for this purpose. These nanocarriers can produce heat, release drugs or stimulate the production of physiologically relevant compounds when illuminated with near-infrared light. The current review summarizes the causes contributing to cancer multidrug resistance. The major types of nanocarriers that have been developed in recent years to overcome these hurdles are described. We focus on nanoparticles that are responsive to near-infrared light and suitable to surmount cancer multidrug resistance. Our review concludes with the bottlenecks that currently restrict the use of nanocarriers in the clinic and an outlook on future directions.