ESTRO 2024 - Abstract Book

S5381

Radiobiology - Tumour biology

ESTRO 2024

Keywords: Palmitoylation, DNA damage response, ZDHHC20

1555

Digital Poster

Nuclear phospho-YB-1: A biomarker of KRAS mutation and a target to radiosensitize colorectal cancers

Konstanze Lettau 1,2 , Stephan Forchhammer 3 , Birgit Fehrenbacher 3 , Shayan Khozooei 1 , Soundaram Veerappan 1 , Marcus Scharpf 4 , Stephan Singer 5 , Gunnar Blumenstock 6 , Irina Bonzheim 5 , Cihan Gani 1 , Mahmoud Toulany 1 1 University Hospital Tübingen, Radiation Oncology, Tübingen, Germany. 2 University Hospital Tübingen, Internal Medicine I, Tübingen, Germany. 3 University Hospital Tübingen, Dermatology, Tübingen, Germany. 4 University Hospital Tübingen, Pathology, Tübingen, Germany. 5 University Hospital Tübingen, Institute of Pathology and Neuropathology, Tübingen, Germany. 6 University Hospital Tübingen, Department of Clinical Epidemiology and Biostatistics, Tübingen, Germany

Purpose/Objective:

The oncoprotein Y-box-binding protein-1 (YB-1) is involved in all cancer features. P90 ribosomal S6 kinase (RSK) and AKT are two important kinases that phosphorylate YB-1 at serine residue 102 (S102). The flavonoid compound fisetin is known to inhibit RSK-mediated YB-1 phosphorylation [1]. The phosphorylation of YB-1 can modulate its binding to DNA and RNA, and as a result, can affect the transcription and translation of other proteins involved in cancer progression. In breast cancer cells, mutant KRAS has been described as a major stimulator of YB-1 phosphorylation in vitro. In the same cells, silencing of YBX1 or KRAS, as well as specific inhibition of S102 phosphorylation, was shown to inhibit DNA double strand break (DSB) repair [2, 3]. KRAS gene is mutated in approximately 45% of colorectal carcinomas (CRC) and is associated with poor prognosis and resistance to therapy. In this study, we investigated an association between S102 phosphorylation of YB-1 in subcellular fractions and mutational status of KRAS in CRC tissues ex vivo . Similarly, the role of YB-1 phosphorylation in DNA DSB repair and cell survival after irradiation was investigated in CRC cells in vitro.

Material/Methods:

Tissue samples from 36 CRC patients (13 male, 23 female) and normal tissue from 5 of the corresponding tumors were obtained from the Biobank of the Faculty of Medicine, University Hospital Tübingen, Germany. The inclusion criteria were defined as Patients with UICC Stage III and IV cancer who were treated between 2018 and 2022. Immunohistochemistry and immunofluorescence staining of phosphorylated YB-1 at S102 were performed. Mutation status of KRAS and other oncogenes was analyzed by next generation sequencing. A KRAS wild-type ( KRAS wt ) CRC cell line, CaCo2, stably transfected with a doxycycline-inducible KRAS G12V expression system [4] was used for the in vitro study. KRAS wt U2OS osteosarcoma cells expressing reporter constructs for DSB repair pathways, i.e. homologous recombination (HR), classical non-homologous end-joining (C-NHEJ) and alternative NHEJ repair pathways (Alt-NHEJ) [5], were used to analyze the underlying repair pathways affected by the inhibition of YB-1 phosphorylation. A γH2AX