Functional studies of membrane-bound and purified human Hedgehog receptor Patched expressed in yeast

Microscale Thermophoresis to Evaluate the Functionality of Heterologously Overexpressed Membrane Proteins in Membrane Preparations

Transmembrane proteins are challenging to express in heterologous systems and to purify, thus any technique enabling to evaluate the functionality of the protein produced prior purification provides a huge step forward. Furthermore, the membrane environment may be critical for the activity of the target protein and accessing information in the membrane fragments instead of solubilizing the target into a detergent that may be unsuitable for its function is key to study and evaluate its activity. Herein, we describe how microscale thermophoresis (MST) was used to evaluate the functionality of membrane proteins directly in host membrane preparation before purification. We give a protocol to measure the affinity between the human Hedgehog (Hh) receptor Ptch1 in yeast plasma membrane and the small molecule PAH, which was shown to inhibit its drug efflux activity.

Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018

Over the past decade, the Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. Since the field continues to expand and novel mechanisms that orchestrate multiple cell death pathways are unveiled, we propose an updated classification of cell death subroutines focusing on mechanistic and essential (as opposed to correlative and dispensable) aspects of the process. As we provide molecularly oriented definitions of terms including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence, and mitotic catastrophe, we discuss the utility of neologisms that refer to highly specialized instances of these processes. The mission of the NCCD is to provide a widely accepted nomenclature on cell death in support of the continued development of the field.

Method to Screen Multidrug Transport Inhibitors Using Yeast Overexpressing a Human MDR Transporter

Multidrug resistance has appeared to mitigate the efficiency of anticancer drugs and the possibility of successful cancer chemotherapy. The Hedgehog receptor Patched is a multidrug transporter expressed in several cancers and as such it represents a new target to circumvent chemotherapy resistance. In this chapter, we describe the screening test developed to identify molecules able to inhibit the drug efflux activity of Patched. This screening test uses yeast overexpressing functional human Patched that have been shown to resist to chemotherapeutic agents. This test can be adapted to other MDR transporters.

Detergent-solubilized Patched purified from Sf9 cells fails to interact strongly with cognate Hedgehog or Ihog homologs

Patched (Ptc) is a twelve-pass transmembrane protein that functions as a receptor for the Hedgehog (Hh) family of morphogens. In addition to Ptc, several accessory proteins including the CDO/Ihog family of co-receptors are necessary for proper Hh signaling. Structures of Hh proteins bound to members of the CDO/Ihog family are known, but the nature of the full Hh receptor complex is not well understood. We have expressed the Drosophila Patched and Mouse Patched-1 proteins in Sf9 cells and find that Sonic Hedgehog will bind to Mouse Patched-1 in isolated Sf9 cell membranes but that purified, detergent-solubilized Ptc proteins do not interact strongly with cognate Hh and CDO/Ihog homologs. These results may reflect a nonnative conformation of detergent-solubilized Ptc or that an additional factor or factors lost during purification are required for high-affinity Ptc binding to Hh.

The Hedgehog receptor patched functions in multidrug transport and chemotherapy resistance

Most anticancer drugs fail to eradicate tumors, leading to the development of drug resistance and disease recurrence. The Hedgehog signaling plays a crucial role during embryonic development, but is also involved in cancer development, progression, and metastasis. The Hedgehog receptor Patched (Ptc) is a Hedgehog signaling target gene that is overexpressed in many cancer cells. Here, we show a link between Ptc and resistance to chemotherapy, and provide new insight into Ptc function. Ptc is cleared from the plasma membrane upon interaction with its ligand Hedgehog, or upon treatment of cells with the Hedgehog signaling antagonist cyclopamine. In both cases, after incubation of cells with doxorubicin, a chemotherapeutic agent that is used for the clinical management of recurrent cancers, we observed an inhibition of the efflux of doxorubicin from Hedgehog-responding fibroblasts, and an increase of doxorubicin accumulation in two different cancer cell lines that are known to express aberrant levels of Hedgehog signaling components. Using heterologous expression system, we stringently showed that the expression of human Ptc conferred resistance to growth inhibition by several drugs from which chemotherapeutic agents such as doxorubicin, methotrexate, temozolomide, and 5-fluorouracil. Resistance to doxorubicin correlated with Ptc function, as shown using mutations from Gorlin's syndrome patients in which the Ptc-mediated effect on Hedgehog signaling is lost. Our results show that Ptc is involved in drug efflux and multidrug resistance, and suggest that Ptc contributes to chemotherapy resistance of cancer cells.

The hedgehog receptor patched is involved in cholesterol transport

Background

Sonic hedgehog (Shh) signaling plays a crucial role in growth and patterning during embryonic development, and also in stem cell maintenance and tissue regeneration in adults. Aberrant Shh pathway activation is involved in the development of many tumors, and one of the most affected Shh signaling steps found in these tumors is the regulation of the signaling receptor Smoothened by the Shh receptor Patched. In the present work, we investigated Patched activity and the mechanism by which Patched inhibits Smoothened.

Methodology/Principal Findings

Using the well-known Shh-responding cell line of mouse fibroblasts NIH 3T3, we first observed that enhancement of the intracellular cholesterol concentration induces Smoothened enrichment in the plasma membrane, which is a crucial step for the signaling activation. We found that binding of Shh protein to its receptor Patched, which involves Patched internalization, increases the intracellular concentration of cholesterol and decreases the efflux of a fluorescent cholesterol derivative (BODIPY-cholesterol) from these cells. Treatment of fibroblasts with cyclopamine, an antagonist of Shh signaling, inhibits Patched expression and reduces BODIPY-cholesterol efflux, while treatment with the Shh pathway agonist SAG enhances Patched protein expression and BODIPY-cholesterol efflux. We also show that over-expression of human Patched in the yeast S. cerevisiae results in a significant boost of BODIPY-cholesterol efflux. Furthermore, we demonstrate that purified Patched binds to cholesterol, and that the interaction of Shh with Patched inhibits the binding of Patched to cholesterol.

Conclusion/Significance

Our results suggest that Patched may contribute to cholesterol efflux from cells, and to modulation of the intracellular cholesterol concentration. This activity is likely responsible for the inhibition of the enrichment of Smoothened in the plasma membrane, which is an important step in Shh pathway activation.

A class of mild surfactants that keep integral membrane proteins water-soluble for functional studies and crystallization

Mixed protein-surfactant micelles are used for in vitro studies and 3D crystallization when solutions of pure, monodisperse integral membrane proteins are required. However, many membrane proteins undergo inactivation when transferred from the biomembrane into micelles of conventional surfactants with alkyl chains as hydrophobic moieties. Here we describe the development of surfactants with rigid, saturated or aromatic hydrocarbon groups as hydrophobic parts. Their stabilizing properties are demonstrated with three different integral membrane proteins. The temperature at which 50% of the binding sites for specific ligands are lost is used as a measure of stability and dodecyl-β-D-maltoside ('C12-b-M') as a reference for conventional surfactants. One surfactant increased the stability of two different G protein-coupled receptors and the human Patched protein receptor by approximately 10°C compared to C12-b-M. Another surfactant yielded the highest stabilization of the human Patched protein receptor compared to C12-b-M (13°C) but was inferior for the G protein-coupled receptors. In addition, one of the surfactants was successfully used to stabilize and crystallize the cytochrome b(6 )f complex from Chlamydomonas reinhardtii. The structure was solved to the same resolution as previously reported in C12-b-M.

Proteins of the Hedgehog signaling pathway as therapeutic targets against cancer

The Hedgehog pathway plays a crucial role in growth and patterning during embryonic development and is involved in stem cell maintenance and proliferation in adult tissues. Mutations that increase the overall activity of the pathway are often associated with a higher incidence of cancers. This article focuses on the mutations, misfoldings and deregulations of the Hedgehog pathway proteins that have been reported to be involved in different tumors, and on small molecules targeting these proteins shown to slow down the growth of certain tumors in various animal models. We propose that proteomics could be a powerful tool to identify new targets of the Hedgehog pathway, enabling the discovery of effective and novel treatments for cancers.

In the cauldron of cell-free synthesis of membrane proteins: playing with new surfactants

Cell-free protein synthesis is a well-known technique for the roles it has played in deciphering the genetic code and in the beginnings of signal sequence studies. Since then, many efforts have been made to optimise this technique and, recently, to adapt it to membrane protein production with yields compatible with structural investigations. The versatility of the method allows membrane proteins to be obtained directly stabilised in surfactant micelles or inserted in a lipidic environment (proteoliposome, bicelle, and nanodisc) at the end of synthesis. Among the surfactants used, non-detergent ones such as fluorinated surfactants proved to be a good alternative in terms of colloidal stability and preservation of the integrity of membrane proteins, as shown for Escherichia coli homo-pentameric channel, MscL (Park et al., Biochem. J., 403: 183-187). Here we report cell-free expression of Escherichia coli leader peptidase (a transmembrane protease), Halobacterium salinarium bacteriorhodopsin (a transmembrane protein binding a hydrophobic cofactor) and E. coli MscL in the presence of non-detergent surfactants, amphipols and fluorinated surfactants in comparison to their expression in classical detergents. The results confirm the potentialities of fluorinated surfactants and, although pointing to limitations in using the first generations amphipols, results are discussed in the light of membrane protein refolding, especially in the case of bacteriorhodopsin. Preliminary experiments using new generations of amphipols supports choices made in developing new molecules.

Stability study of the human G-protein coupled receptor, Smoothened

Smoothened is a member of the G-protein coupled receptor (GPCR) family responsible for the transduction of the Hedgehog signal to the intracellular effectors of the Hedgehog signaling pathway. Aberrant regulation of this receptor is implicated in many cancers but also in neurodegenerative disorders. Despite the pharmacological relevance of this receptor, very little is known about its functional mechanism and its physiological ligand. In order to characterize this receptor for basic and pharmacological interests, we developed the expression of human Smoothened in the yeast Saccharomyces cerevisiae and Smoothened was then purified. Using Surface Plasmon Resonance technology, we showed that human Smoothened was in a native conformational state and able to interact with its antagonist, the cyclopamine, both at the yeast plasma membrane and after purification. Thermostability assays on purified human Smoothened showed that this GPCR is relatively stable in the classical detergent dodecyl-beta-d-maltoside (DDM). The fluorinated surfactant C(8)F(17)TAC, which has been proposed to be less aggressive towards membrane proteins than classical detergents, increased Smoothened thermostability in solution. Moreover, the replacement of a glycine by an arginine in the third intracellular loop of Smoothened coupled to the use of the fluorinated surfactant C(8)F(17)TAC during the mutant purification increased Smoothened thermostability even more. These data will be very useful for future crystallization assays and structural characterization of the human receptor Smoothened.