The Anticancer Potential of Doxycycline and Minocycline—A Comparative Study on Amelanotic Melanoma Cell Lines

Malignant melanoma is still a serious medical problem. Relatively high mortality, a still-growing number of newly diagnosed cases, and insufficiently effective methods of therapy necessitate melanoma research. Tetracyclines are compounds with pleiotropic pharmacological properties. Previously published studies on melanotic melanoma cells ascertained that minocycline and doxycycline exerted an anti-melanoma effect. The purpose of the study was to assess the anti-melanoma potential and mechanisms of action of minocycline and doxycycline using A375 and C32 human amelanotic melanoma cell lines. The obtained results indicate that the tested drugs inhibited proliferation, decreased cell viability, and induced apoptosis in amelanotic melanoma cells. The treatment caused changes in the cell cycle profile and decreased the intracellular level of reduced thiols and mitochondrial membrane potential. The exposure of A375 and C32 cells to minocycline and doxycycline triggered the release of cytochrome c and activated initiator and effector caspases. The anti-melanoma effect of analyzed drugs appeared to be related to the up-regulation of ERK1/2 and MITF. Moreover, it was noticed that minocycline and doxycycline increased the level of LC3A/B, an autophagy marker, in A375 cells. In summary, the study showed the pleiotropic anti-cancer action of minocycline and doxycycline against amelanotic melanoma cells. Considering all results, it could be concluded that doxycycline was a more potent drug than minocycline.

Comparing the folding landscapes of evolutionarily divergent procaspase-3

All caspases evolved from a common ancestor and subsequently developed into two general classes, inflammatory or apoptotic caspases. The caspase-hemoglobinase fold has been conserved throughout nearly one billion years of evolution and is utilized for both the monomeric and dimeric subfamilies of apoptotic caspases, called initiator and effector caspases, respectively. We compared the folding and assembly of procaspase-3b from zebrafish to that of human effector procaspases in order to examine the conservation of the folding landscape. Urea-induced equilibrium folding/unfolding of procaspase-3b showed a minimum three-state folding pathway, where the native dimer isomerizes to a partially folded dimeric intermediate, which then unfolds. A partially folded monomeric intermediate observed in the folding landscape of human procaspase-3 is not well-populated in zebrafish procaspase-3b. By comparing effector caspases from different species, we show that the effector procaspase dimer undergoes a pH-dependent conformational change, and that the conformational species in the folding landscape exhibit similar free energies. Together, the data show that the landscape for the caspase-hemoglobinase fold is conserved, yet it provides flexibility for species-specific stabilization or destabilization of folding intermediates resulting in changes in stability. The common pH-dependent conformational change in the native dimer, which yields an enzymatically inactive species, may provide an additional, albeit reversible, mechanism for controlling caspase activity in the cell.

Microtubule disassembly by caspases is the rate-limiting step of cell extrusion

Epithelial cell death is essential for tissue homeostasis, robustness and morphogenesis. The expulsion of epithelial cells following caspase activation requires well-orchestrated remodeling steps leading to cell elimination without impairing tissue sealing. While numerous studies have provided insight about the process of cell extrusion, we still know very little about the relationship between caspase activation and the remodeling steps of cell extrusion. Moreover, most studies of cell extrusion focused on the regulation of actomyosin and steps leading to the formation of a supracellular contractile ring. However, the contribution of other cellular factors to cell extrusion has been poorly explored. Using the Drosophila pupal notum, a single layer epithelium where most extrusion events are caspase-dependent, we first showed that the initiation of cell extrusion and apical constriction are surprisingly not associated with the modulation of actomyosin concentration/dynamics. Instead, cell apical constriction is initiated by the disassembly of a medio-apical mesh of microtubules which is driven by effector caspases. We confirmed that local and rapid increase/decrease of microtubules is sufficient to respectively expand/constrict cell apical area. Importantly, the depletion of microtubules is sufficient to bypass the requirement of caspases for cell extrusion. This study shows that microtubules disassembly by caspases is a key rate-limiting steps of extrusion, and outlines a more general function of microtubules in epithelial cell shape stabilisation.

Effect of glyprolines on serum caspase levels under “social” stress

Objective. To investigate the effect of glyprolines on the levels of initiating and effector caspases in the serum of white rats under "social" stress. Materials and methods. The study was conducted on 90 white male rats of 6 months of age. All manipulations with animals were carried out in accordance with international and domestic requirements for working with laboratory animals. When modeling "social" stress, groups of animals with aggressive and submissive behavior were formed. Laboratory animals, taking into account the types of behavior, were divided into groups (n=10): a group of intact males (control); a group of animals exposed to" social " stress for 20 days (stress); groups of individuals who received intraperitoneal Selank (Thr-Lys-Pro-Arg-Pro-Gly-Pro), Pro-Gly-Pro, Pro-Gly-Pro-Leu at doses of 100 mcg/kg / day from the 1st day of stress exposure within a 20- day course. The effect of neuropeptides on the activity of apoptosis processes was evaluated by determining the level of initiating and effector caspases (caspase-8 and caspase-3) (ELISA Kit for Caspase-8 and ELISA Kit for Caspase-3; USA) in the blood serum of white rats by enzyme immunoassay. Results. According to the results of the study, it was found that under conditions of "social" stress, an increase in apoptotic processes was observed, accompanied by an increase in the level of caspase-3 and caspase-8 in the blood serum of white rats. The introduction of the studied compounds against the background of stress contributed to a decrease in the level of the studied indicators, which is most likely due to the presence of antiapoptotic action in glyprolins due to inhibition of the caspase-dependent cascade of apoptosis reactions, as a result of which the destruction of cellular structures occurs by hydrolysis of nuclear lamina, cleavage of adhesive proteins, destruction of the cytoskeleton. Conclusion. Thus, the conducted study established the presence of Thr-Lys-Pro-Arg-Pro-Gly-Pro (Selank), Pro-Gly-Pro and Pro-Gly-Pro-Leu under conditions of stress-induced antiapoptotic activity due to inhibition of the caspase-dependent cascade of apoptosis reactions.

EFFECT OF MELANOCORTINS AND EXPERIMENTAL SOCIAL STRESS ON THE LEVEL OF CASPASE-3 AND CASPASE-8

At present the study of stress-generating effects and key mechanisms of regulation of apoptosis remain in the focus of attention of researchers. Stress causes dysfunctions of many body systems which lead to disruption of homeostasis and molecular cell mechanisms of programmed cell death. In this context, the problem of pharmacological regulation and correction of these disorders poses an urgent problem. Neuropeptide compounds such as melanocortins are interesting in this direction as regulators and correctors. Under conditions of experimental social stress activation of apoptotic processes was established due to an increase in the level of caspase-3 and caspase-8. The studied neuropeptides Semax (ACTH (4-7)-Pro-Gly-Pro) and ACTH (6-9)-Pro-Gly-Pro exhibit antiapoptotic effects under conditions of induced social stress in rats. This action of neuropeptides is manifested by a decrease in the activity of the initiating and effector caspases in the blood serum of experimental animals.

Evolution of the folding landscape of effector caspases

Caspases are a family of cysteinyl proteases that control programmed cell death and maintain homeostasis in multicellular organisms. The caspase family is an excellent model to study protein evolution because all caspases are produced as zymogens (procaspases) that must be activated to gain full activity; the protein structures are conserved through hundreds of millions of years of evolution; and some allosteric features arose with the early ancestor while others are more recent evolutionary events. The apoptotic caspases evolved from a common ancestor into two distinct subfamilies: monomers (initiator caspases) or dimers (effector caspases). Differences in activation mechanisms of the two subfamilies, and their oligomeric forms, play a central role in the regulation of apoptosis. Here, we examine changes in the folding landscape by characterizing human effector caspases and their common ancestor. The results show that the effector caspases unfold by a minimum three-state equilibrium model at pH 7.5, where the native dimer is in equilibrium with a partially folded monomeric (procaspase-7, common ancestor) or dimeric (procaspase-6) intermediate. In comparison, the unfolding pathway of procaspase-3 contains both oligomeric forms of the intermediate. Overall, the data show that the folding landscape was first established with the common ancestor and was then retained for >650 million years. Partially folded monomeric or dimeric intermediates in the ancestral ensemble provide mechanisms for evolutionary changes that affect stability of extant caspases. The conserved folding landscape allows for the fine-tuning of enzyme stability in a species-dependent manner while retaining the overall caspase-hemoglobinase fold.

An Integrative Apoptotic Reaction Model for extrinsic and intrinsic stimuli

Apoptosis, a form of programmed cell death central to all multicellular organisms, plays a key role during organism development and is often misregulated in cancer. Devising a single model applicable to distinct stimuli and conditions has been limited by lack of robust observables. Indeed, previous numerical models have been tailored to fit experimental datasets in restricted scenarios, failing to predict response to different stimuli. We quantified the activity of three caspases simultaneously upon intrinsic or extrinsic stimulation to assemble a comprehensive dataset. We measured and modeled the time between maximum activity of intrinsic, extrinsic and effector caspases, a robust observable of network dynamics, to create the first integrated Apoptotic Reaction Model (ARM). Observing how effector caspases reach maximum activity first irrespective of stimuli used, led us to identify and incorporate a missing feedback into a successful model for extrinsic stimulation. By simulating different recently performed experiments, we corroborated that ARM adequately describes them. This integrated model provides further insight into the indispensable feedback from effector caspase to initiator caspases.

Proapoptotic RHG genes and mitochondria play a key non-apoptotic role in remodelling the Drosophila sensory system

Caspases are best known for their role in programmed cell death but have also been found to be important in several non-apoptotic phenomena such as cell fate specification, cell migration and terminal differentiation. The dynamics of such sub-lethal caspase events and the molecular mechanisms regulating them are still largely unknown. As more tools for visualizing and manipulating caspase activation in vivo become available, greater insights into this biology are being made. Using a new and sensitive in vivo effector caspase probe, called SR4VH, we demonstrate that effector caspases are activated in pruning sensory neurons earlier than previously thought and that the level of caspase activation in these neurons is consistently lower than in neurons undergoing cell death. We reveal that Grim and Reaper, two of the four pro-apoptotic RHG proteins, are required for sensory neuron pruning and that disrupting the dynamics of the mitochondrial network prevents effector caspase activation in both pruning and dying sensory neurons. Overall, our findings demonstrate that a sublethal deployment of the ‘apoptotic machinery’ is critical for remodelling dendrites and also reveal a direct link between mitochondria and sensory neuron cell death in vivo.