Stathmin potentiates vinflunine and inhibits Paclitaxel activity

TAUCON and TAUCOM: A novel biosensor based on fluorescence resonance energy transfer for detecting tau hyperphosphorylation-associated cellular pathologies

Tauopathies are neurodegenerative diseases characterized by abnormal conformational changes in tau protein. Early hyperphosphorylation-induced conformational changes are considered a hallmark of tauopathy, but real-time tracking methods are lacking. Here, we present two novel fluorescence resonance energy transfer (FRET)-based tau biosensors that detect such changes with high spatiotemporal resolution at the single-cell level. The TAUCON biosensor measures instantaneous conformational changes in hyperphosphorylated tau within 20 min, while the TAUCOM biosensor detects changes in the paper-clip structure of microtubule-associated tau. Our biosensors provide faster and more precise detection than conventional methods and can serve as valuable tools for investigating the initial causes, mechanisms, progression, and treatment of tauopathies.

Long Noncoding RNAs in Taxane Resistance of Breast Cancer

Breast cancer is a common cancer in women and a leading cause of mortality. With the early diagnosis and development of therapeutic drugs, the prognosis of breast cancer has markedly improved. Chemotherapy is one of the predominant strategies for the treatment of breast cancer. Taxanes, including paclitaxel and docetaxel, are widely used in the treatment of breast cancer and remarkably decrease the risk of death and recurrence. However, taxane resistance caused by multiple factors significantly impacts the effect of the drug and leads to poor prognosis. Long noncoding RNAs (lncRNAs) have been shown to play a significant role in critical cellular processes, and a number of studies have illustrated that lncRNAs play vital roles in taxane resistance. In this review, we systematically summarize the mechanisms of taxane resistance in breast cancer and the functions of lncRNAs in taxane resistance in breast cancer. The findings provide insight into the role of lncRNAs in taxane resistance and suggest that lncRNAs may be used to develop therapeutic targets to prevent or reverse taxane resistance in patients with breast cancer.

Stathmin dynamics modulate the activity of eribulin in breast cancer cells

Stathmin, a phosphoprotein that modulates microtubule dynamics, is highly expressed in breast cancer cells. Eribulin, a microtubule‐depolymerizing agent, is used to treat patients with advanced breast cancer. However, the detailed mechanisms underlying the action of eribulin during microtubule catastrophe, and the interaction between eribulin and stathmin dynamics, remain unclear. Here, we investigated the role of stathmin in the antiproliferative activity of eribulin in breast cancer cells. Eribulin induced phosphorylation of stathmin in MCF7 and MDA‐MB‐231 cells; this was attenuated by an inhibitor of protein kinase A (H89) and an inhibitor of Ca²⁺/calmodulin‐dependent kinase II (KN62). In addition, expression of phosphorylated stathmin was reduced by the protein phosphatase PP2A activator FTY720 but increased by the PP2A inhibitor okadaic acid. Of note, expression of PP2A subunits in eribulin‐treated cells decreased, although eribulin did not affect the phosphatase activity of recombinant PP2A directly. Furthermore, the antiproliferative effect of eribulin was stronger in stathmin‐overexpressing cells. These results suggest that stathmin dynamics are closely associated with the antiproliferative effects of eribulin and stathmin is a possible biomarker for predicting the therapeutic effects of eribulin in breast cancer patients.

Therapeutic strategies to overcome taxane resistance in cancer

One of the primary causes of attenuated or loss of efficacy of cancer chemotherapy is the emergence of multidrug resistance (MDR). Numerous studies have been published regarding potential approaches to reverse resistance to taxanes, including paclitaxel (PTX) and docetaxel, which represent one of the most important classes of anticancer drugs. Since 1984, following the FDA approval of paclitaxel for the treatment of advanced ovarian carcinoma, taxanes have been extensively used as drugs that target tumor microtubules. Taxanes, have been shown to affect an array of oncogenic signaling pathways and have potent cytotoxic efficacy. However, the clinical success of these drugs has been restricted by the emergence of cancer cell resistance, primarily caused by the overexpression of MDR efflux transporters or by microtubule alterations. In vitro and in vivo studies indicate that the mechanisms underlying the resistance to PTX and docetaxel are primarily due to alterations in α-tubulin and β-tubulin. Moreover, resistance to PTX and docetaxel results from: 1) alterations in microtubule-protein interactions, including microtubule-associated protein 4, stathmin, centriole, cilia, spindle-associated protein, and kinesins; 2) alterations in the expression and activity of multidrug efflux transporters of the ABC superfamily including P-glycoprotein (P-gp/ABCB1); 3) overexpression of anti-apoptotic proteins or inhibition of apoptotic proteins and tumor-suppressor proteins, as well as 4) modulation of signal transduction pathways associated with the activity of several cytokines, chemokines and transcription factors. In this review, we discuss the abovementioned molecular mechanisms and their role in mediating cancer chemoresistance to PTX and docetaxel. We provide a detailed analysis of both in vitro and in vivo experimental data and describe the application of these findings to therapeutic practice. The current review also discusses the efficacy of different pharmacological modulations to achieve reversal of PTX resistance. The therapeutic roles of several novel compounds, as well as herbal formulations, are also discussed. Among them, many structural derivatives had efficacy against the MDR phenotype by either suppressing MDR or increasing the cytotoxic efficacy compared to the parental drugs, or both. Natural products functioning as MDR chemosensitizers offer novel treatment strategies in patients with chemoresistant cancers by attenuating MDR and increasing chemotherapy efficacy. We broadly discuss the roles of inhibitors of P-gp and other efflux pumps, in the reversal of PTX and docetaxel resistance in cancer cells and the significance of using a nanomedicine delivery system in this context. Thus, a better understanding of the molecular mechanisms mediating the reversal of drug resistance, combined with drug efficacy and the application of target-based inhibition or specific drug delivery, could signal a new era in modern medicine that would limit the pathological consequences of MDR in cancer patients.

Role of Tau as a Microtubule-Associated Protein: Structural and Functional Aspects

Microtubules (MTs) play a fundamental role in many vital processes such as cell division and neuronal activity. They are key structural and functional elements in axons, supporting neurite differentiation and growth, as well as transporting motor proteins along the axons, which use MTs as support tracks. Tau is a stabilizing MT associated protein, whose functions are mainly regulated by phosphorylation. A disruption of the MT network, which might be caused by Tau loss of function, is observed in a group of related diseases called tauopathies, which includes Alzheimer’s disease (AD). Tau is found hyperphosphorylated in AD, which might account for its loss of MT stabilizing capacity. Since destabilization of MTs after dissociation of Tau could contribute to toxicity in neurodegenerative diseases, a molecular understanding of this interaction and its regulation is essential.

How Cancer Cells Resist Chemotherapy: Design and Development of Drugs Targeting Protein-Protein Interactions

Background:

Resistance toward chemotherapeutics is one of the main obstacles on the way to effective cancer treatment. Personalization of chemotherapy could improve clinical outcome. However, despite preclinical significance, most of the potential markers have failed to reach clinical practice partially due to the inability of numerous studies to estimate the marker’s impact on resistance properly.

Objective:

The analysis of drug resistance mechanisms to chemotherapy in cancer cells, and the proposal of study design to identify bona fide markers.

Methods:

A review of relevant papers in the field. A PubMed search with relevant keywords was used to gather the data. An example of a search request: drug resistance AND cancer AND paclitaxel.

Results:

We have described a number of drug resistance mechanisms to various chemotherapeutics, as well as markers to underlie the phenomenon. We also proposed a model of a rational-designed study, which could be useful in determining the most promising potential biomarkers.

Conclusion:

Taking into account the most reasonable biomarkers should dramatically improve clinical outcome by choosing the suitable treatment regimens. However, determining the leading biomarkers, as well as validating of the model, is a work for further investigations.

Characterization of Microtubule-Associated Proteins (MAPs) and Tubulin Interactions by Isothermal Titration Calorimetry (ITC)

Microtubules are highly dynamic structures which play a central role in many cellular processes such as cell division, intracellular transport, and migration. Their dynamics is tightly regulated by stabilizing and destabilizing microtubule-associated proteins (MAPs), such as tau and stathmin. Many approaches have been developed to study interactions between tubulin and MAPs. However, isothermal titration calorimetry (ITC) is the only direct thermodynamic method that enables a full thermodynamic characterization of the interaction after a single titration experiment. We provide here the protocols to apply ITC to tubulin interaction with either stathmin or tau, which will help to avoid the common pitfalls in this very powerful and sensitive method.

Vinblastine differs from Taxol as it inhibits the malignant phenotypes of NSCLC cells by increasing the phosphorylation of Op18/stathmin

Taxol (paclitaxel) and vinblastine (VBL) are both efficacious chemotherapeutic agents that target the microtubules of tumor cells, but each functions in a mutual antagonistic manner. Op18/stathmin is a small molecular phosphoprotein which promotes depolymerization of microtubules. Non-small cell lung cancer (NSCLC) NCI-H1299 cells were employed to compare the curative effects of VBL and Taxol and explore the correlation between drug sensitivity and Op18/stathmin signaling. The present study found that VBL obviously promoted cellular apoptosis and initiated activation of caspase 3 and 9, and inhibited cell proliferation and colony formation, as well as cell migration in the NCI-H1299 cells in contrast with Taxol. VBL did not affect the expression of Op18/stathmin, but increased its phosphorylation at all 4 serine sites. Conversely, Taxol mainly decreased the expression of Op18/stathmin and the phosphorylation at Ser25 and Ser63 sites. Silencing of Op18/stathmin by RNA interference (RNAi) led to a great reduction in the differences in the cell proliferation inhibition between VBL and Taxol. VBL treatment notably weakened the expression of PP2A, Bcl-2, NF-κB and interleukin-10 (IL-10) and autocrine IL-10 compared with Taxol; whereas PP2A was substantially increased following Taxol induction. High expression of Op18/stathmin was found to be negatively correlated with the sensitivity of Taxol in the NSCLC cells, but had a minor impact on VBL cytotoxicity. These findings revealed that both VBL and Taxol induce cell apoptosis through Op18/stathmin, but the mechanisms are completely different. VBL is an attractive alternative to the treatment of Taxol-resistant tumors with high expression of Op18/stathmin.

Sequential binding of calcium ions to the B-repeat domain of SdrD from Staphylococcus aureus

Biofilms of live bacteria forming on medical devices and implants contribute significantly to bacterial blood dissemination and to the spread of nosocomial infections. Cell surface SdrD protein plays a key role in the attachment of Staphylococcus aureus to the extracellular matrix (ECM) and in the formation of biofilm. SdrD binds calcium ions using its B1-B5 region bearing EF-hand Ca-binding sites, leading to conformational changes in the structure of SdrD. This alters the distance between the bacterial surface and the ECM-interacting domain of SdrD in a spring-like fashion, participating in bacterial attachment. In this study we investigated calcium binding to EF-hand sites of SdrD using isothermal titration calorimetry and determined the impact of this process on SdrD's thermodynamic stability. This allowed us to propose a model of B1-B5 reorganization upon binding of calcium and to get new insight into the molecular mechanism of SdrD's action.

Avoiding Buffer Interference in ITC Experiments: A Case Study from the Analysis of Entropy-Driven Reactions of Glucose-6-Phosphate Dehydrogenase

Isothermal titration calorimetry (ITC) is a label-free technique that allows the direct determination of the heat absorbed or released in a reaction. Frequently used to determining binding parameters in biomolecular interactions, it is very useful to address enzyme-catalyzed reactions as both kinetic and thermodynamic parameters can be obtained. Since calorimetry measures the total heat effects of a reaction, it is important to consider the contribution of the heat of protonation/deprotonation that is possibly taking place. Here, we show a case study of the reaction catalyzed by the glucose-6-phosphate dehydrogenase (G6PD) from Leuconostoc mesenteroides. This enzyme is able to use either NAD(+) or NADP(+) as a cofactor. The reactions were done in five buffers of different enthalpy of protonation. Depending on the buffer used, the observed calorimetric enthalpy (ΔH(cal)) of the reaction varied from -22.93 kJ/mol (Tris) to 19.37 kJ/mol (phosphate) for the NADP(+)-linked reaction, and -11.67 kJ/mol (Tris) to 7.32 kcal/mol or 30.63 kJ/mol (phosphate) for the NAD(+) reaction. We will use this system as an example of how to extract proton-independent reaction enthalpies from kinetic data to ensure that the reported accurately represent the intrinsic heat of reaction.