Modulating the Structure of EGFR with UV Light: New Possibilities in Cancer Therapy

Abstract

The epidermal growth factor receptor (EGFR) is a member of the ErbB family of receptor tyrosine kinases. EGFR is activated upon binding to e.g. epidermal growth factor (EGF), leading to cell survival, proliferation and migration. EGFR overactivation is associated with tumor progression. We have previously shown that low dose UVB illumination of cancer cells overexpressing EGFR prior to adding EGF halted the EGFR signaling pathway. We here show that UVB illumination of the extracellular domain of EGFR (sEGFR) induces protein conformational changes, disulphide bridge breakage and formation of tryptophan and tyrosine photoproducts such as dityrosine, N-formylkynurenine and kynurenine. Fluorescence spectroscopy, circular dichroism and thermal studies confirm the occurrence of conformational changes. An immunoassay has confirmed that UVB light induces structural changes in the EGF binding site. A monoclonal antibody which competes with EGF for binding sEGFR was used. We report clear evidence that UVB light induces structural changes in EGFR that impairs the correct binding of an EGFR specific antibody that competes with EGF for binding EGFR, confirming that the 3D structure of the EGFR binding domain suffered conformational changes upon UV illumination. The irradiance used is in the same order of magnitude as the integrated intensity in the solar UVB range. The new photonic technology disables a key receptor and is most likely applicable to the treatment of various types of cancer, alone or in combination with other therapies.

EGF Functionalized Polymer-Coated Gold Nanoparticles Promote EGF Photostability and EGFR Internalization for Photothermal Therapy

“…EGF is a protein where these reactions will occur in the presence of UVB light leading to protein conformational changes and to loss of functionality. EGF is a natural ligand for EGFR with significant biomedical importance in cancer treatment and diagnostic [19]. Changes in the fluorescence spectra of the extrinsic fluorescence probe SYPRO ® Orange confirmed structural changes of EGF induced by temperature (Fig 2), prolonged illumination at 295 nm (Fig 4) and pH, as its fluorescent emission is enhanced upon binding to hydrophobic regions of the protein [20].…”

“…The presence of oxidative conditions induced by light can lead to the oxidation of the aromatic residues in proteins [14,15,19,31,41]. UVB excitation of aromatic residues in proteins leads to the disruption of SS bridges [14–17,19] and to the formation of photoproducts, such as N-formylkynurenine (NFK), kynurenine (Kyn) [25,42] and dityrosine (DT) [26].…”

“…UVB excitation of aromatic residues in proteins leads to the disruption of SS bridges [14–17,19] and to the formation of photoproducts, such as N-formylkynurenine (NFK), kynurenine (Kyn) [25,42] and dityrosine (DT) [26]. Since 295 nm excites specifically Trp residues, it is very likely that the photoproducts formed are Trp derivatives such as NFK and Kyn and not Tyr derivatives like DT.…”

“…Furthermore, UV excitation of the side chains of aromatic residues induces the disruption of disulphide (SS) bonds, mediated by an electron transfer process, leading to the formation of a transient disulphide electron adduct and to changes in the fluorescence quantum yield of proteins [16,17]. The effect of UV light on the structure and function of key medically relevant proteins, such as Epidermal Growth Factor Receptor (EGFR) [19], insulin [14] and plasminogen [15] has been reported.…”

Diverse effects of a 445 nm diode laser on isometric contraction of the rat aorta

“…Recently, ultraviolet (UV) lasers have been suggested to be useful for cancer therapy owing to their ability to modulate the structure of EGFR [1]. However, UV lasers also affect normal cells.…”