Overview
It is becoming increasingly apparent that to more fully understand
how cells operate as integrated molecular systems, an intimate
combination of quantitative experiment and computational modeling
is required. This is clearly the case for the complex receptor-mediated
signaling networks activated by growth factors, cytokines, and
extracellular matrix. Accordingly, we are attempting to develop
multi-variable, multi-parametric 'systems biology' measurement
and analysis methodologies useful for investigating signaling networks
and cell functions they regulate.
Research Summary
The epidermal growth factor receptor [EGFR] system provides one
especially attractive paradigm for this quantitative systems biology
approach, because of the substantial amount of information regarding
its key components, its highly conserved evolutionary nature, and
its strong relevance to development, physiology, and disease. A
central aim of our laboratory is to generate a fusion of experiment
and modeling to address a variety of questions about how the EGFR
system operates as a highly modulated dynamic 'circuit' to help
regulate a variety of important cell functions including survival,
proliferation, and migration. These studies are connected to analogous
investigations across a broader context involving regulatory signaling
networks activated by other growth factors, cytokines, and matrix
components as well as environmental stresses, with cancer as a
major application area. Examples of current project areas include
the following.
Autocrine Ligand/Receptor Loops: An intriguing
feature of the EGFR system is that it commonly operates in autocrine
fashion, with
its family of ligands (including EGF, TGFa, HB-EGF, and amphiregulin)
being synthesized as transmembrane precursors whose release is
governed by regulated proteolytic cleaveage at specific sites.
The extent to which subsequently released ligand is self-captured
by the producing cell or a proximal neighbor as opposed to escaping
to distal tissue regions determines the strength of resulting
signaling via EGFR-mediated pathways. The molecular and cellular
properties
governing autocrine ligand capture are poorly understood, so
we are attempting to elucidate and manipulate them. Additionally,
we are trying to discern what physiological roles EGFR autocrine
loops play in embryonic development and adult tissue organization
and homeostasis, and how pathological dysregulation can occur
related
to cancer or other hypertrophic diseases. At present attention
is focused on mammary and lung epithelial cells.
Endocytic Trafficking
and Signaling: Activation of diverse signaling
pathways downstream of EGFR can vary with the location of the
receptor/ligand complex, as modulated by endocytic trafficking
processes of internalization
and recycling. Consequently, factors which influence EGFR trafficking
can substantially alter signaling network activity. This effect
can have serious implications for resulting cell behavorial
functions because certain functions, such as motility, depend to
greater
or lesser degrees on the activation levels of different EGFR-induced
pathways. As one important example, expression of a second
member of the EGFR family, HER2 (or erbB2), is strongly correlated
with
invasive tumor progression in carcinomas. Thus, we are exploring
the possibility that a significant portion of this dysregulation
of epithelial cell proliferation and migration behavior arises
from altered EGFR trafficking due to HER2/EGFR interactions,
with a focus on mammary and prostate epithelial cells.
Regulation
of Cell Migration: Migration is a behavioral cell
function important in a wide spectrum of physiological, pathological,
and
technological problems, e.g., organ development, tissue organization,
inflammatory and immune responses, tumor invasion and metastasis,
wound healing, and biomaterials colonization. This cell behavior
requires exquisite coordination of a number of dynamic biophysical
processes including membrane extension, cell/matrix adhesion,
and cytoskeletal force generation and transmission, which
are regulated
by signals from growth factor and matrix receptors. We are
especially interested in biophysical process regulation by
EGFR-mediated
signals as they synergize with those from extracellular matrix
components
such as fibronectin and collagen. Our recent efforts have
focused on two EGFR-activated pathways that appear to be specific
to
motogenic cell responses, apart from mitogenic responses,
in fibroblasts
and epithelial cells, rendering them promising targets for
cancer therapeutics: PLCg, a governor of cytoskeleton/membrane
interactions,
and calpain, actually a family of intracellular cysteine
proteases whose enyzmatic activities are modulated by phosphorylation
as well as calcium-binding. Intriguingly, activation of both
of
these pathways downstream of EGFR appears to be spatially-restricted
in manner enabling the asymmetric force transmission from
cytoskeleton
to extracellular matrix necessary for translating intracellular
forces into cell locomotion. We are accordingly testing whether
inhibition of these pathways may be useful for reducing invasiveness
and metastatic capability of breast and prostate carcinoma
cells.
Regulation of Cell Death/Survival Decisions: Programmed
cell death, or apoptosis, is similarly involved in various
problem
areas. The
execution phase of apoptosis, largely carried out by the
caspases, is primarily governed by upstream signaling networks
integrating
inputs from potentially competing death and survival stimuli,
which comprise cytokines, growth factors, extracellular
matrix, and environmental
insults such as radiation and chemical toxins. We are attempting
to quantitatively characterize the dependence of execution
phase operation on a dynamic set of signaling network activities,
with
emphasis on certain EGFR-mediated pathways potentially
serving in key pro-survival roles. As part of this effort we are
developing high-throughput quantitative assays for specific
kinase activities
on particular downstream substrates, and are applying a
battery
of computational modeling (e.g., Bayesian, vector state-space,
and physico-chemical kinetic) methodologies to analyze
relationships elucidating how signaling network activities downstream
of
pro-death and pro-survival stimuli may govern cell death-vs-survival
responses.
Selected Publications
Sachs, K., O. Perez, D. Pe'er, D.A. Lauffenburger, and G.P. Nolan. Causal Protein Signaling Networks Derived From Multiparameter Single-Cell Data, Science 308: 523-529 (2005).
Hautaniemi, S., S. Kharait, A. Iwabu, A. Wells, and D.A. Lauffenburger. Modeling of Signal-Response Cascades using Decision Tree Analysis, Bioinformatics 21: 2027-2035 (2005).
Hendriks, B.S., G. Orr, A. Wells, H.S. Wiley, and D.A. Lauffenburger. Parsing ERK Activation Reveals Quantitatively Equivalent Contributions from EGFR and HER2 in Human Mammary Epithelial Cells, J. Biol. Chem. 280: 6157-6169 (2005).
Janes, K.A., J. R. Kelly, S. Gaudet, J.G.Albeck, P.K. Sorger, and D.A. Lauffenburger. Cue-Signal-Response Analysis of TNF-Induced Apoptosis by Partial Least Squares Regression of Dynamic Multi-Variate Signaling Network Measurements, J. Comp. Biol. 11: 544-561 (2004).
Prudhomme, W., K. Duggar, G.Q. Daly, P.W. Zandstra, and D.A. Lauffenburger. Multi-Variate Proteomic Analysis of Murine Embryonic Stem Cell Self-Renewal vs Differentiation Behavior, Proc. Natl. Acad. Sci. USA 101: 2900-2905 (2004).
Wiley, H.S., S.Y. Shvartsman, and D.A. Lauffenburger. Computational Modeling of the EGF Receptor System: A Paradigm for Systems Biology, Trends Cell Biol. 13: 43-50 (2003).
Search PubMed for Lauffenburger Lab publications; also see Lab website for a complete list. |
