# X-Ray Exposure Induces Structural Changes in Human Breast Proteins

## TL;DR

X-rays used in breast cancer radiotherapy can damage proteins in healthy tissue, potentially leading to tissue stiffening and healing issues.

## Contribution

This study reveals structural changes in extracellular matrix proteins and intracellular proteins due to therapeutic X-ray doses.

## Key findings

- 50 Gy X-ray exposure fragmented collagen I α chains in purified protein solutions.
- X-ray exposure increased collagen I binding to plasma fibronectin and altered peptide yields in basement membrane proteins.
- Intracellular proteins like RPS3, MeCP2, and calnexin also showed structural changes after X-ray exposure.

## Abstract

During radiotherapy, X-rays can deliver significant doses of ionising radiation to both cancerous and healthy tissue, often leading to undesirable side effects that compromise patient outcomes. While the cellular effects of such therapeutic X-ray exposures are well studied, the impact on extracellular matrix (ECM) proteins remains poorly understood. This study characterises the response of ECM proteins, including the major tissue components collagen I and fibronectin (FN), to X-ray doses similar to those used in clinical practice (50 Gy, as employed in breast radiotherapy, and 100 Gy), using a combination of gel electrophoresis, biochemical assays, and mass spectrometry-based peptide location fingerprinting (PLF) analysis. In purified protein solutions, 50 Gy X-ray exposure led to the fragmentation of constituent collagen I α chains. Irradiation of purified plasma FN (pFN) induced localised changes in peptide yields (detected by liquid chromatography and tandem mass spectrometry (LC-MS/MS) and PLF) and enhanced its binding to collagen I. In complex environments, such as newly synthesised fibroblast-derived ECM and mature ex vivo breast tissue, X-ray exposure induced peptide yield changes in not only collagen I and FN but also key basement membrane proteins, including collagen IV, laminin, and perlecan. Intracellular proteins associated with gene expression (RPS3, MeCP2), the cytoskeleton (moesin, plectin), and the endoplasmic reticulum (calnexin) were also found to be impacted. These X-ray-induced structural changes may impair the ECM integrity and alter cell–ECM interactions, with potential implications for tissue stiffening, fibrosis, and impaired wound healing in irradiated tissues.