M phase phosphoprotein 1 is a human plus-end-directed kinesin-related protein required for cytokinesis.

International audienceThe human M phase phosphoprotein 1 (MPP1), previously identified through a screening of a subset of proteins specifically phosphorylated at the G2/M transition (Matsumoto-Taniura, N., Pirollet, F., Monroe, R., Gerace, L., and Westendorf, J. M. (1996) Mol. Biol. Cell 7, 1455-1469), is characterized as a plus-end-directed kinesin-related protein. Recombinant MPP1 exhibits in vitro microtubule-binding and microtubule-bundling properties as well as microtubule-stimulated ATPase activity. In gliding experiments using polarity-marked microtubules, MPP1 is a slow molecular motor that moves toward the microtubule plus-end at a 0.07 microm/s speed. In cycling cells, MPP1 localizes mainly to the nuclei in interphase. During mitosis, MPP1 is diffuse throughout the cytoplasm in metaphase and subsequently localizes to the midzone to further concentrate on the midbody. MPP1 suppression by RNA interference induces failure of cell division late in cytokinesis. We conclude that MPP1 is a new mitotic molecular motor required for completion of cytokinesis

STOP Proteins are Responsible for the High Degree of Microtubule Stabilization Observed in Neuronal Cells

Neuronal differentiation and function require extensive stabilization of the microtubule cytoskeleton. Neurons contain a large proportion of microtubules that resist the cold and depolymerizing drugs and exhibit slow subunit turnover. The origin of this stabilization is unclear. Here we have examined the role of STOP, a calmodulin-regulated protein previously isolated from cold-stable brain microtubules. We find that neuronal cells express increasing levels of STOP and of STOP variants during differentiation. These STOP proteins are associated with a large proportion of microtubules in neuronal cells, and are concentrated on cold-stable, drug-resistant, and long-lived polymers. STOP inhibition abolishes microtubule cold and drug stability in established neurites and impairs neurite formation. Thus, STOP proteins are responsible for microtubule stabilization in neurons, and are apparently required for normal neurite formation

In vitro and in vivo intracellular delivery of quantum dots by maurocalcine

International audienceMaurocalcine is a new member of the increasing family of cell penetrating peptides. We report for the first time that this peptide is able to deliver quantum dots inside a variety of cells, both in vitro and in vivo. In vivo, maurocalcine produces intracellular delivery of the nanoparticles without affecting the relative distribution of quantum dots within organs. The data stress out that maurocalcine can be used for intracellular delivery of functionalised nanoparticles in vivo

Maurocalcine-derivatives as biotechnological tools for the penetration of cell-impermeable compounds: Technological value of a scorpion toxin

Maurocalcine is a unique toxin in that its natural pharmacological target in vivo, the ryanodine receptor, is localized inside cells and not at the cell surface as commonly observed for most toxins. According to the membrane topology of the ryanodine receptor, the binding site of maurocalcine is localized within the cytoplasm. Application of maurocalcine to myotubes in culture induces calcium release via the ryanodine receptor within seconds indicating that the peptide reaches its binding site via a rapid and efficient diffusion through the plasma membrane. Analysis of the maurocalcine amino-acid sequence indicates that it is a heavily positively charged peptide, a property shared with many cell-penetrating peptides. A closer examination of the 3D structure of maurocalcine further illustrates that most of its positively charged residues are located on one face of the molecule according to a distribution that resembles that seen in Tat and penetratin, two cell penetrating peptides. Along with its unique cell penetrating properties, maurocalcine has also the ability to act as a vector for the intracellular delivery of various many cargo molecules or nanoobjects. Many key cell penetration properties of maurocalcine have been defined using a biotinylated version of the peptide that was coupled to a fluorescent streptavidin. Various structure-function strategies have been developed to isolate new maurocalcine analogues presenting the characteristic cell penetration properties without the undesired pharmacological activity. Examples of research and technological applications will be presented in which maurocalcine may prove a powerful delivery vector. By its amazing diversity of potential applications, this peptide opens a new trend of research in the toxin field

: Maurocalcine as good doxorubicin delivery vector

International audiencePURPOSE: The aim of this study is to overcome tumour cell resistance that generally develops after administration of commonly used anti-cancer drugs, such as doxorubicin. METHODS: Recently, cell penetrating peptides have been used for their ability to deliver non-permeant compounds into cells. One such cell penetrating peptide, maurocalcine, has been isolated from the venom of a Tunisian scorpion. Herein, we report the effects of doxorubicin covalently coupled to an analogue of maurocalcine on drug-sensitive or drug-resistant cell lines MCF7 and MDA-MB 231. RESULTS: We demonstrated the in vitro anti-tumoral efficacy of the doxorubicin maurocalcine conjugate. On a doxorubicin-sensitive cancer cell line, the maurocalcine-conjugated form appears slightly less efficient than doxorubicin itself. On the contrary, on a doxorubicin-resistant cancer cell line, doxorubicin coupling allows to overcome the drug resistance. This strategy can be generalized to other cell penetrating peptides since Tat and penetratin show similar effects. CONCLUSION: We conclude that coupling anti-tumoral drugs to cell penetrating peptides represent a valuable strategy to overcome drug resistance

Design of a disulfide-less, pharmacologically inert, and chemically competent analog of maurocalcine for the efficient transport of impermeant compounds into cells.

International audienceMaurocalcine is a 33-mer peptide initially isolated from the venom of a Tunisian scorpion. It has proved itself valuable as a pharmacological activator of the ryanodine receptor and has helped the understanding of the molecular basis underlying excitation-contraction coupling in skeletal muscles. Because of its positively charged nature, it is also an innovative vector for the cell penetration of various compounds. We report a novel maurocalcine analog with improved properties: (i) the complete loss of pharmacological activity, (ii) preservation of the potent ability to carry cargo molecules into cells, and (iii) coupling chemistries not affected by the presence of internal cysteine residues of maurocalcine. We did this by replacing the six internal cysteine residues of maurocalcine by isosteric 2-aminobutyric acid residues and by adding an additional N-terminal biotinylated lysine (for a proof of concept analog) or an N-terminal cysteine residue (for a chemically competent coupling analogue). Additional replacement of a glutamate residue by alanyl at position 12 further improves the potency of these analogues. Coupling to several cargo molecules or nanoparticles are presented to illustrate the cell penetration potency and usefulness of these pharmacologically inactive analogs