HspB1 dynamic phospho-oligomeric structure dependent interactome as cancer therapeutic target

Human HspB1 (Hsp27), a molecular chaperone bearing tumorigenic and metastatic roles, is characterized by its dynamic phosphorylation and heterogenous oligomerization in response to changes in cell physiology. The phenomenon is particularly intense and specific when cells are exposed to different death inducers. This favors the hypothesis that the structural organization of HspB1 acts as a sensor which, through reversible modifications, allows cells to adapt and/or mount a protective response. A large number of HspB1 interacting partners have already been described in the literature. Specific changes in oligomerphosphorylation organization may therefore allow HspB1 to interact with the more appropriate polypeptides and to subsequently modulate their folding/activity and/or half-life. This could indirectly link HspB1 to multiple cellular functions and could explain the apparently unrelated effects associated to its over- or underexpression. In cancer, HspB1 is tumorigenic, stimulates metastasis and provide cancer cells with resistance to many anti-cancer drugs, so compounds aimed at disrupting HspB1 deleterious pro-cancer activity are actively looked for. One example, is brivudine that impairs HspB1 ability to recognize pathological protein substrates and appears as a promising anti-cancer drug. Similarly, we have observed that peptide aptamers that specifically interfere with HspB1 structural organization reduced its anti-apoptotic and tumorigenic activities. We propose that, in addition to RNA interference approaches, the tumorigenic activity of HspB1 could be inhibited by altering HspB1 structural organization and consequently its interaction with inappropriate procancerous polypeptide partners. Hence, developping HspB1 structure-based interfering strategies could lead to new anti-cancer drugs discovery.

Targeting heat shock protein 27 (HspB1) interferes with bone metastasis and tumour formation in vivo

Background:

The small stress heat shock protein 27 (Hsp27) has recently turned as a promising target for cancer treatment. Hsp27 upregulation is associated with tumour growth and resistance to chemo- and radio-therapeutic treatments, and several ongoing drugs inhibiting Hsp27 expression are under clinical trial. Hsp27 is now well described to counteract apoptosis and its elevated expression is associated with increased aggressiveness of several primary tumours. However, its role in the later stage of tumour progression and, more specifically, in the later and most deadly stage of tumour metastasis is still unclear.

Methods/results:

In the present study, we showed by qRT–PCR that Hsp27 gene is overexpressed in a large fraction of the metastatic breast cancer area in 53 patients. We further analysed the role of this protein in mice during bone metastasis invasion and establishment by using Hsp27 genetically depleted MDA-MB231/B02 human breast cancer cell line as a model. We demonstrate that Hsp27 silencing led to reduced cell migration and invasion in vitro and that in vivo it correlated with a decreased ability of breast cancer cells to metastasise and grow in the skeleton.

Conclusion:

Altogether, these data characterised Hsp27 as a potent therapeutic target in breast cancer bone metastasis and skeletal tumour growth.

Inhibition of heat shock protein 27 (HspB1) tumorigenic functions by peptide aptamers

Human heat shock protein 27 (Hsp27, HspB1) is an anti-apoptotic protein characterized for its tumorigenic and metastatic properties, and now referenced as a major therapeutic target in many types of cancer. Hsp27 biochemical properties rely on a structural oligomeric and dynamic organization. Downregulation by small interfering RNA or inhibition with dominant-negative mutant have proven their efficiency to counteract the anti-apoptotic and protective properties of Hsp27. In this study, we report the isolation and characterization of Hsp27-targeted molecules interfering with its structural organization. Using the peptide aptamer (PA) strategy, we isolated PAs that specifically interact with Hsp27 and not with the other members of the small heat shock protein family. In mammalian cell cultures, PAs expression perturbed the dimerization and oligomerization of Hsp27, and acted as negative regulators of the anti-apoptotic and cytoprotective activities of this protein. Further studies analyzing SQ20B cell xenografts in immunocompromised mice showed that PAs strongly reduced tumor development through cell cycle arrest. Our data suggest that PAs could provide a potential tool to develop strategies for the discovery of Hsp27 chemical inhibitors.

Experimental study of carbon sequestration reactions controlled by the percolation of CO2-rich brine through peridotites

Carbonation of ultramafic rocks in geological reservoirs is, in theory, the most efficient way to trap CO2 irreversibly; however, possible feedback effects between carbonation reactions and changes in the reservoir permeability must be considered to realistically assess the efficiency and sustainability of this process. We investigated changes in the hydrodynamic properties of sintered dunite samples by means of percolation experiments, under conditions analogous to that of in situ carbonation. Our results show that carbonation efficiency is controlled by the local renewal of the reactants and the heterogeneity of the pore structure. Preferential flow zones are characterized by the formation of magnetite and of a silica-rich layer at the olivine surfaces, which eventually inhibits olivine dissolution. Conversely, sustainable olivine dissolution together with coprecipitation of magnesite, siderite, and minor Mg-TOT-phyllosilicates, occur in reduced-flow zones. Thus carbonate precipitation only decreases porosity in zones where diffusion-controlled transport is dominant. Consequently, while high flow rates will decrease the carbonation efficiency of the reservoir and low flow rates may reduce the permeability irreversibly close to the injection point, moderate injection rates will ensure a partial carbonation of the rock and maintain the reservoir permeability.

Anisotropy of thermal diffusivity in the upper mantle

Heat transfer in the mantle is a key process controlling the Earth's dynamics. Upper-mantle mineral phases, especially olivine, have been shown to display highly anisotropic thermal diffusivity at ambient conditions, and seismic anisotropy data show that preferred orientations of olivine induced by deformation are coherent at large scales (>50 km) in the upper mantle. Thus heat transport in the upper mantle should be anisotropic. But the thermal anisotropy of mantle minerals at high temperature and its relationship with deformation have not been well constrained. Here we present petrophysical modelling and laboratory measurements of thermal diffusivity in deformed mantle rocks between temperatures of 290 and 1,250 K that demonstrate that deformation may induce a significant anisotropy of thermal diffusivity in the uppermost mantle. We found that heat transport parallel to the flow direction is up to 30 per cent faster than that normal to the flow plane. Such a strain-induced thermal anisotropy implies that the upper-mantle temperature distribution, rheology and, consequently, its dynamics, will depend on deformation history. In oceans, resistive drag flow would result in lower vertical diffusivities in both the lithosphere and asthenosphere and hence in less effective heat transfer from the convective mantle. In continents, olivine orientations frozen in the lithosphere may induce anisotropic heating above mantle plumes, favouring the reactivation of pre-existing structures.