Clinical studies indicate that the family of epidermal growth factor receptors (EGFR/ERBB) has important roles in the progression of breast cancer. Accordingly, many EGFR/ERBB inhibitors are used as drugs for the treatment of this disease. However, hypoxia in solid tumors is believed to contribute to resistance to EGFR/ERBB targeted therapies. A positive correlation exists between the activation of EGFR and the synthesis of hypoxia-inducible factor-1 alpha (HIF-1 alpha), a key regulator of the hypoxic response. Our preliminary results indicate, that the main player of hydroxylation-driven HIF-1 alpha degradation prolyl hydroxylase 2 (PHD2) greatly contributes to the stability and signaling of EGFR.
To characterize the relationships between PHD2 and EGFR in vivo we have analyzed the biopsies from breast cancer patients. To further understand the connection between these proteins on a molecular level, we have established MDA-MB-231 breast cancer cell line with a stable knockdown of PHD2. EGFR levels were checked on the mRNA and protein level by qPCR and Western blot; possible alterations in the EGFR signaling in the established cell line were checked by EGF stimulation followed by the measurement of the EGFR and kinases phosphorylation. Proteasomal, lysosomal degradation of EGFR and half-life of the receptor were assessed by treatment of cells with corresponding inhibitors. Functional assays, examining cellular proliferation and migration complemented the above-mentioned experiments.
Our study is the first to describe the relations between PHD2 and EGFR in both preclinical and clinical models of breast cancer. We identify PHD2 as a novel contributor to EGFR signaling in breast cancer by showing its direct participation in the regulation of EGFR stability.
Since the search for novel signaling interplays is a prerequisite for the development of better treatment options of breast cancer, we believe that this novel finding is of potential value for clinicians and medical researchers.
Clinical trial identification
Legal entity responsible for the study
University of Oulu
FEBS, Finnish Center of International Mobility (CIMO), European Association for Cancer Research (EACR), Biocenter Oulu, University of Oulu, Jane and Aatos Erkko Foundation, Finnish Academy of Sciences, the Sigrid Juselius Foundation.
All authors have declared no conflicts of interest.