Mimicking the Function of Signaling Proteins: Toward Artificial Signal Transduction Therapy

Summary

We present guidelines for developing synthetic 'chemical transducers' that can induce communication between naturally unrelated proteins. In addition, detailed protocols are presented for synthesizing and testing a specific 'transducer' that enables a growth factor to activate a detoxifying enzyme and consequently, to regulate the cleavage of an anticancer prodrug.

Abstract

Signal transduction pathways, which control the response of cells to various environmental signals, are mediated by the function of signaling proteins that interact with each other and activate one other with high specificity. Synthetic agents that mimic the function of these proteins might therefore be used to generate unnatural signal transduction steps and consequently, alter the cell's function. We present guidelines for designing 'chemical transducers' that can induce artificial communication between native proteins. In addition, we present detailed protocols for synthesizing and testing a specific 'transducer', which can induce communication between two unrelated proteins: platelet-derived growth-factor (PDGF) and glutathione-S-transferase (GST). The way by which this unnatural PDGF-GST communication could be used to control the cleavage of an anticancer prodrug is also presented, indicating the potential for using such systems in 'artificial signal transduction therapy'. This work is intended to facilitate developing additional 'transducers' of this class, which may be used to mediate intracellular protein-protein communication and consequently, to induce artificial cell signaling pathways.

Introduction

Signal transduction pathways play a significant role in virtually every cellular process and allow the cell to rapidly respond to environmental signals.¹ These pathways are often triggered by the binding of a signaling molecule to an extracellular receptor, which results in activation of intracellular enzymes. Amplification and propagation of this signal within the cell is mediated by the function of signaling proteins that form a network of protein-protein interactions in which enzymes are reversibly activated with high specificity. Because dysregulation of these networks frequently leads to cancer development, there has been much interest in establishing ....

Protocol

1. Synthesis of the 'Chemical Transducer'

1. Preliminary Preparations
   1. Prepare 2 M triethylammonium acetate (TEAA) buffer by mixing 278 ml of triethylamine with 114 ml of acetic acid and 400 ml of ultrapure water. Adjust the pH to 7 and add water to a final volume of 1 L. Keep it in a dark bottle.
      Note: This solution is stable for years.
   2. Prepare a 5 mM ascorbic acid solution by dissolving 18 mg of ascorbic acid in 20 ml of ultrapure water. Use a fresh solution; the solution is stable for one day.
   3. Prepare a 10 mM Cu(II)/Tris(benzyltriazolylmethyl)amine (TBTA) solution by dissolving 25 mg of copper(II) sulfate pe....

Results

The design, synthesis, and mechanism of action of a 'chemical transducer' that can induce artificial communication between PDGF and GST are presented in Figure 2. The structure of the 'transducer' integrates a PDGF DNA aptamer and a bis-ethacrynic amide (bEA), which is a known GST inhibitor (Figure 2a).¹⁹ These binders enable the 'transducer' to bind both PDGF and GST with different affinities, namely, with dissociation .......

Discussion

We presented a method for designing and testing of a 'chemical transducer' that can induce artificial communication between two naturally unrelated proteins, GST and PDGF, without modifying the native proteins. The unnatural GST-PDGF communications could be detected in real time by using enzymatic assays that follow the changes in the activity of GST in the presence of the 'chemical transducer' and increasing the concentrations of PDGF. In addition to detecting the activation of GST by PDGF, these assays were used to fol.......

Materials

Name	Company	Catalog Number	Comments
1-chloro-2,4-dinitrobenzene	Sigma-Aldrich	237329
Acetic acid	Bio Lab	01070521
Acetnitrile	J.T.Baker	9017-03
Ascorbic acid	Sigma-Aldrich	A4544
Copper(II) Sulfate pentahydrate	Merck-Millipore	102790
Dimethyl sulfoxide	Merck-Millipore	802912
Dulbecco's Phosphate Buffered Saline	Biological Industries	02-023-5A
Ethacrynic acid	Tokyo Chemical Industry Co. Ltd	E0526
Glutathione-s-transferase M1-1	Israel Structural Proteomics Center (Weizmann Institute of Science, Rehovot, Israel)
JS-K	Sigma-Aldrich	J4137
L-glutathione reduced	Sigma-Aldrich	G4251
Magnesium Chloride	J.T.Baker	0162
nitrate/nitrite colorimetric assay kit	Cayman Chemical	780001
Oligonucleotides	W. M. Keck Foundation Biotechnology at Yale University		custom order
PDGF-BB	Israel Structural Proteomics Center (Weizmann Institute of Science, Rehovot, Israel)
TBTA	Sigma-Aldrich	678937
Triethylamine	Sigma-Aldrich	T0886
Desalting column	GE Healthcare	illustra MicroSpin G-25 Columns
HPLC	Waters	2695 separation module
HPLC column	Waters	XBridgeTM OST C18 column (2.5 μM, 4.6 mm × 50 mm)
HPLC column	Waters	XBridgeTM OST C18 column (2.5μM, 10 mm × 50 mm)
Plate reader	BioTek	synergy H4 hybrid