Signalling cascades triggered by receptor tyrosine kinases (RTKs) are frequently activated in human cancer. To comprehend the role of RTKs in tumours and devise strategies to intercede with their function, detailed understanding of their mechanisms of action including ligand regulation and activation of cytoplasmic signal transducers, is required.
This proposal focuses on the ErbB and RET subfamilies of RTKs based upon their established involvement in prevalent types of human cancer. Members of the ErbB RTK family including EGFR, ErbB2 and ErbB3, are involved in human tumours by overexertion and constitutive receptor activation. While autocrine stimulation of the EGFR in tumours has been established, the role of natural ligands for the related ErbB receptors remains elusive. RET which encodes a RTK lacking a known ligand, is activated by structural abnormalities as a dominant transforming gene in various tumour types.
To characterise ligand-receptor interactions relevant to malignancy, we will attempt to identify and isolate novel ligands regulating the activity of ErbB2, ErbB3 and RET. Among known ligands, the role of HRG on ErbB2, ErbB3 and ErbB4 activity will be determined in model systems.
Furthermore, the function of membrane-anchored forms of TGF and HRG will be analysed, including possible intrinsic signalling properties associated with their cytoplasmic domains. Known ligand-receptor interactions will be exploited to specifically target tumour cells overexpressing ErbB family receptors in vitro and in vivo using cytotoxic T lymphocytes with recombinantly engineered T cell receptor components.
Mechanisms of receptor heterodimerisation including ligand-independent activation will be determined for ErbB2 and ErbB3 synergy, whereas the activating potential of novel mutations in the ErbB2 juxtamembrane region will be evaluated for ErbB2 signalling properties.
Pathophysiologically relevant model systems will be established to measure ErbB and RET receptor function. Reversion of neoplastic phenotypes induced by MEN2A, MEN2B and mutated ErbB2, will be attempted by use of mutation-specific antisense oligonucleotides. In the case of activated RET alleles, this approach will be complemented by investigating the potential of certain Hirschsprung alleles to function as dominant-negatives. At the substrate level, research is focused on targets of mitogenic control relevant for human cancer. Thus, substrates in ErbB receptors and RET pathways segregating with increased transforming potential are of particular interest including those shared between RET and ErbB2 as well as substrates specifically associated with signal transduction by RET-MEN2B, ErbB2-ErbB3 heterodimers and point-mutated ErbB2. Moreover, among a battery of tyrosine kinase substrates analysed, shc and eps8 are frequently tyrosine phosphorylated in human tumours projecting their role as universal targets for tyrosine kinases activated in human tumours.
To expand the mechanistic understanding of eps8 and shc phosphorylation in tumours, functional interactions between both substrates will be investigated, and target proteins in the signalling cascade will be characterised. The physiologic role of eps8 will be investigated by gene targeting in mice. To facilitate rapid identification of tumours with activated tyrosine kinases that would be amenable for therapeutic approaches involving tyrosine kinase inhibitors, screening tests based upon shc and eps8 phosphorylation will be developed. Furthermore, this approach will provide the basis for the identification of novel tyrosine kinases selected on the basis of their involvement in human neoplasia.
Funding SchemeCSC - Cost-sharing contracts
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