Project Summary:
Understanding the detailed mechanisms that underlie proliferative signal transduction pathways is of critical
importance for developing strategies for diagnosis and treatment of human cancer. Because most proliferative
pathways are critical for the functioning of all normal cells, the development of cancer-cell-selective interventions
without off-target effects is tremendously important yet highly challenging. The research proposed in this grant
application focuses on unique ‘players’ in proliferative signaling, the guanine nucleotide exchange factors (GEFs)
from the Dbl (diffuse B cell lymphoma) family.
GEFs control proliferative signaling by stimulating nucleotide exchange on the small GTPases, Rho, Rac, and
Cdc42. In doing so, GEFs regulate numerous cellular activities such as gene expression, cytoskeletal
rearrangements, protein synthesis, and metabolism. Gain-of-function mutations in GEFs are associated with
multiple human cancers, and GEFs from the Dbl family constitute one of the largest families of proto-oncogenes.
Although different Dbl-family GEFs share similar mechanisms of action, their expression is extremely tissue- and
cell-specific, and their respective mutated forms are associated with distinct and different cancers. Thus,
intervention with GEF signaling may be extremely useful in multiple, seemingly unrelated malignant diseases.
The proposed work relies on our recent discovery of a novel tyrosine phosphorylation sequence motif
(TEXXYVXXL) that regulates the activity of some Dbl-like GEFs implicated in human cancers. We hypothesize
that selective interreference with this phosphorylation comprises a unique, novel and effective selective
intervention approach in relevant cancers. This proof-of-principle proposal focuses on Tiam1, a GEF whose
dysregulation drives colorectal tumorigenesis and metastasis. We propose to decipher the molecular
mechanisms and functional outcomes of TEXXYVXXL phosphorylation in Tiam1, and to test novel reagents that
target Tiam1’s tyrosine phosphorylation as selective intervention tools. In Specific Aim 1 we will decipher the role
of TEXXYVXXL phosphorylation in regulating Tiam1’s key activities, i.e. GTPase activation, cell invasion and
proliferation in vitro, and tumorigenesis and metastasis in vivo. In Specific Aim 2, we will evaluate the utility of
novel reagents that target Tiam1’s TEXXYVXXL phosphorylation site for intervention in a mouse model of colon
cancer. These proof-of-concept experiments in cells and animals will open the door for future development and
translational work in GEF-associated malignancies.