Tumor cells signaling

Molecular Oncology
Instituto de Investigaciones Biomédicas “Alberto Sols” CSIC-UAM (IIBM)

Metastasis is the primary cause of clinical recurrence of breast tumors and mortality of patients. Metastasis formation is a complex process involving multiple mechanisms and signaling pathways, genetic and epigenetic factors, systemic and tissular factors, elements in tissues surrounding the primary tumor, the immune system, and the receptor organs. We plan to study three systems implicated in the development of breast cancer metastases: i) the tyrosine kinase receptor ErbB2; ii) the non-receptor tyrosine kinase c-Src; and iii) the adapter protein Grb7, all of them interconnected and regulated by calmodulin (CaM), as we have previously demonstrated. CaM is a modulator in eukaryotic cells transducing the calcium signal generated upon activation by a variety of effectors, and that regulates many cellular processes including: cell proliferation, apoptosis and autophagy, all of them playing a fundamental role in tumorigenesis and tumor progression. ErbB2, c-Src and Grb7 (including its truncated variant Grb7V) have been identified as important components of signaling pathways that control the invasive and metastatic capacities of various carcinomas, including human breast adenocarcinomas. Our working hypothesis is that targeting the CaM-binding domain(s) (CaM-BDs) of ErbB2, c-Src and/or Grb7 could disrupt their functionalities and hence metastases formation. As a preliminary validation of our working hypothesis, we have demonstrated: i) the direct interaction of CaM with ErbB receptors (most significantly the epidermal growth factor receptor (EGFR/ErbB1) and ErbB2), c-Src and Grb7; ii) the inhibition of the ligand-dependent activation of the EGFR and the proliferation of EGFR-overexpressing cells using a modified cell-penetrating peptide corresponding to the CaM-BD of the EGFR (of similar characteristics than the one in ErbB2); and iii) the inhibition in vivo of tumor growth and associated angiogenesis in glioma upon expression of a deletion mutant of Grb7 (Grb7Δ) lacking the regulatory region where CaM binds. This project aims to study three specific points, which could form the groundwork for new potential therapeutic strategies for inhibiting the formation of metastases in human breast tumors using as therapeutic targets the CaM-BDs of ErbB2, c-Src and Grb7. Thus, the specific objectives of this project are: i) to identify the molecular mechanisms by which CaM regulates the tyrosine kinase activity of both ErbB2 and c-Src, and the functionality of Grb7; ii) to determine whether the mutated forms of Grb7 and Grb7V, lacking the CaM-BD regulatory region (Grb7Δ and Grb7VΔ) are able to inhibit the development of metastases generated after implantation of human breast adenocarcinoma cells in immunosuppressed animal models; and iii) to determine whether the ectopic in situ-expression of peptides, and/or the administration of their cell-penetrating variants, corresponding to the sequences of the CaM-BDs of ErbB2, c-Src and/or Grb7 (the latter identical to the one in Grb7V) inhibit the formation of metastases by implanted human breast adenocarcinoma cells. The identification of new targets to inhibit the metastatic process in breast tumors, such as the CaM-BDs of ErbB2, c-Src, and Grb7/Grb7V, could be the first step in the development of new therapeutic strategies directed against said regulatory domains of these proteins, what could open the possibility of using in the clinic similar strategies in the future.

Molecular Biomedicine