Home Institution
Johann Wolfgang Goethe Universität, Frankfurt am Main

Host Institution
Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, Ontario
Mentor: Prof. Igor Stagljar

E-Mail: philipp-david@gmx.de

• The great working atmosphere in CCBR labs
• St. Patrick’s Day
• Spin Gallery, 1100 Queen Street West
• O’ Gradys @ College Street (I’m NOT kidding!)

• Toronto is food city – and everything is very affordable. Enjoy Indian cuisine on Baldwin Street (9-10$ buffet), take the yellow subway line up north to Finch and go all you can eat sushi at “My Sushi” restaurant (18$), go to College St. and eat Shawarma for a few bucks, meet meat in Grill Time Korean BBQ House right at College and Yonge, take your lab staff to Dim Sum places in Chinatown… become a student discount member of GoodLife Fitness Club to lose some dispensable pounds.
• Create a free student bank account at Deutsche Bank to enjoy the advantages of free banking and money transfer at each Scotia Bank branch and Scotia bank machines. Nonetheless get a credit card if you don’t have one.
  
• If you are interested in Toronto’s club scene, don’t miss out on Queen Street West’s area around the old Drake Hotel (Spin Gallery, The Social, Drake Underground). Local heroes as well as internationally established artists show up for inspiring and euphoric performances. Check city magazines such as NOW for upcoming events.
• Take the chance to go to Niagara Falls by Casino bus on College St. It only costs you five dollars! Pay 30 CAD, and get 25 CAD back in Niagara Fallsview Casino later on. Enjoy all you can eat buffet for 20 bucks!

Institution:
Prof. Igor Stagljar’s Laboratory, Centre For Cellular & Biomolecular Research (CCBR), University of Toronto, Toronto, Ontario

Introduction:
The ErbB receptor family consists of four receptor tyrosine kinases, namely EGFR, ErbB2/Her2/Neu, ErbB3/Her3 and ErbB4/Her4. All of them lead to a variety of signal transduction cascades after ligand binding, hetero – or homodimerization of the receptors and autophosphorylation on specific intracellular tyrosine residues. These signal cascades include – among many others - the PI3-kinase cascade, the Ras/Raf/MEK pathway and the Jak / STAT pathway.
Besides point mutation and chromosomal rearrangement, which is a common genetic feature of non-solid tumors, DNA amplification counts as one of the most important mechanism for activation of oncogenes, leading to an undirected, uncontrolled mutated cell proliferation process. Because receptor dimerization does not only depend on ligand binding anymore, overexpression of these receptors as a result of DNA amplification plays a major role in many human cancers, e.g. aggressive breast cancers, colon cancer subtypes, certain soft tissue sarcomas and neuroblastomas.

Outline of Methods Used:
For the screening of protein-protein interactions of the mentioned ErbB receptors the full-length cDNA sequence of each of the receptors (the “baits”) was cloned in a special vector yielding a strong promoter sequence and the C-terminal part of ubiquitin followed by an artificial transcription factor. On the other hand a special set of putative “prey” cDNA interacting partners was fused to the N-terminal part of ubiquitin to build up a human fetal brain genomic library. The baits where tested upon self-activation by co-transformation with a set of S. cerevisiae proteins of the endoplasmatic reticulum respectively the plasma membrane which were either fused to wild-type NubI moiety or to a mutated NubG moiety where a point mutation in a hydrophobic residue circumvents the recognization of the two ubiquitin parts and therefore avoids the activation of proteolytic cleavage by ubiquitin-specific proteases (UBPs). Upon the study of these interactions using the Membrane – based Yeast Two-Hybrid (MbYTH) approach (Stagljar et al. (1998) Proc. Acad. Sci. USA 95, 5187-5192

Results:
The study of the ErbB receptor family protein-protein interactions have revealed a new spectrum of interacting proteins, among them tumor suppressors, classical oncogenes, cell-cycle regulating proteins and adapter proteins which are able to amplify ligand signals to equated signal cascades within the cell. Studying the cross-talk interactions will deliver a complete view at the whole human EGF receptor interactome.

Discussion:
Once interacting partners are confirmed in human cell lines not only the receptor tyrosine kinases themselves could be therapeutic targets to treat cancer as it is already the case for t(9;22) CML patients using Imatinib but anti-cancer treatment could extend to highly-selective tyrosine kinase inhibitors and cell-cycle-regulating proteins or genome guardians such as p53, where studies with a chemical compound have shown that this compound actively reconstitutes mutant p53 and upon this restoring process can induce wild-type-p53 dependent selective apoptosis in cancer cell lines.