Mechanisms Regulating Cell Polarization and Protein Targeting
research interest is to understand the mechanisms of cell polarization and the
functional consequences of this polarization during development and
cancerogenesis. In the last several years my laboratory has focused on three
distinct but related projects: regulation and function of asymmetric cell
division, mechanisms of cancer metastasis and regulation of epithelia
polarization in vitro and in vivo. The latest findings and future
directions for these projects are described below.
1. Molecular mechanisms of epithelial cells polarization.
Epithelial cells are structurally and functionally
polarized to transport specific molecules while maintaining a trans-epithelial
barrier. This cellular asymmetry is essential for the proper functioning of
epithelial tissues and depends on polarized endocytic transport routes.
Additionally, epithelial cells coordinate their polarization with neighboring
cells to form an apical lumen, a key step in the establishment of renal and gut
architecture, and thereby function. Indeed, malfunctions in epithelial cell
polarization and apical lumen formation are responsible for a variety of renal
and intestinal disorders, such as polycystic kidney disease, renal tubular
acidosis, microvilli inclusion disease and diabetes insipidus. This project aims to fill critical gaps
in our understanding of epithelial cell biology, including what are the
molecular mechanisms mediating coordinated formation of apical lumen during
epithelia morphogenesis and function.
recent advances in our understanding of the mechanisms mediating lumen
formation, many questions remains unanswered. How are endosomes targeted during
apical lumen formation? How do cells establish the site of single apical lumen?
Do the mechanisms of lumen formation established in vitro also apply to epithelial morphogenesis in vivo? Addressing these pivotal and unanswered questions forms the backbone of
this project. This study is designed to analyze the machinery of apical
lumen formation using in vitro (MDCK
cells three dimensional cultures) and in
vivo (zebrafish) models.
2. Regulation breast cancer metastasis.
Remodelling of the extracellular matrix (ECM) is a key process during
tumor growth and metastasis and is mediated via formation of structures, known
as invadopodia, and targeted secretion of enzymes, known as matrix
metalloproteinases (MMPs). Invadopodia are actin-rich structures that degrade
the ECM and have been shown to be important for tumor progression. MMP2/9 also
have been shown to be enriched at the invadopodia and are known for their roles
in breast tumor growth/metastasis.
As a result, MMP2/9 have
emerged as possible therapeutic targets. Unfortunately, clinical trials
directly inhibiting MMP2/9 have proven ineffective, mostly due to adverse side
effects and pre-existing high levels of secreted MMPs. It has been proposed
that targeting the machinery specifically mediating MMP secretion at cancer
cell invadopodia is more effective approach. However, little is known about
targeted MMP2/9 secretion since most of the studies have
focused on the mechanisms mediating ECM and cell adhesion and actin dynamics
during metastasis. In contrast, very few studies have analysed the machinery
mediating targeted MMP secretion in cancer cells in vitro and tested these mechanisms in vivo. The main goal of
this project is to combine studies using basic cell and molecular biology
techniques with more translational in vivo approaches to define and
systematically analyse novel pathways that mediate targeted MMP transport and
secretion during breast cancer metastasis. The strength of this
project is combining of the unique expertise from my lab (cell biology and Rab
GTPases), Dr. Paul Jedlicka (microRNA and pathology) and Dr. Tracy Lyons
(breast cancer and xenograft assays) laboratories. This combination will allow
us to comprehensively test these hypotheses in
vitro and in vivo.
3. The role of midbodies in regulating cancer and stem
Cytokinesis is the final stage of the cell cycle
resulting in physical separation of daughter cells. At late mitosis, the mother
cell divides by the formation of a cleavage furrow, leaving two daughter cells
connected by a thin intercellular bridge (ICB). The resolution of this bridge,
abscission, is mediated by coordinated action between specialized recycling
endosomes and cytoskeleton. During ingression of the cleavage furrow, the
central spindle microtubules are compacted to form the structure known as the
midbody (MB). The MB is situated within the ICB, with the abscission usually
occurring at one side of the MB. As a result of this one-sided (asymmetric)
abscission, only one daughter cell inherits the post-mitotic MB. These
post-mitotic MBs can then either accumulate in the cytoplasm or be degraded.
Interestingly, recent studies have identified post-mitotic MBs as novel
signaling platforms regulating stem cell fate and proliferation. Indeed, stem
cells were shown to accumulate post-mitotic MBs and the induction of MB
accumulation leads to reprogramming of cell fate and conversion to
highly-proliferative stem cell-like phenotypes. Despite the importance of MBs
in determining cell fate and proliferative capacity, the mechanisms that
regulate asymmetric MB inheritance and post-mitotic degradation remains
completely unknown. As the result, the main goal of this project is to identify the factors mediating MB
inheritance and accumulation, and to test the role of these factors in
regulating stem cell fate and differentiation.