Regulation of Cell signaling by Cell adhesion Molecules - Group Orian-Rousseau
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From bench to bedside – Interview with Prof. Dr. Véronique Orian-Rousseau
Outline of Research
Cell Adhesion Molecules (CAMs) located at the cell surface, mediate cell-cell and cell-to-extracellular matrix contacts. Since they are tightly connected to signaling pathways, they can induce signaling in response to the microenvironment. Such a CAM is CD44, a family of transmembrane glycoproteins that mediates proliferation, differentiation, migration and survival. The members of the CD44 family differ in the extracellular domain where ten variant exons are subjected to alternative splicing.
We have discovered that several CD44 isoforms act as co-regulators of several signaling pathways amongst which Receptor Tyrosine Kinases such as MET, VEGFR-2, EGFR, G-Protein-Coupled Receptors such as CXCR4 and members of the Wnt pathway such as LRP6. CD44 isoforms act as signaling hubs integrating the signals from the microenvironment.
Our aim is to study the molecular mechanisms of action of CD44 isoforms and to design inhibitory molecules that could be used in diseases such as cancer (pancreatic cancer, colorectal cancer, breast cancer and leukemia) and liver diseases.
Figure 1 : Molecular mechanism of action of CD44 isoforms:
CD44-Receptor Tyrosine Kinases: CD44v6 acts as a co-receptor for various receptor tyrosine kinases (RTKs) amongst which VEGFR2 and Met, two major RTKs that are instrumental for angiogenesis and metastasis.The role of CD44v6 for these RTKs is two-fold: The ectodomain of CD44v6 is involved in RTK activation and the cytoplasmic domain promotes signaling upon binding to the cytoskeleton through ERM (Ezrin-Radixin-Moesin) proteins. CD44v6 takes part in tumor progression and metastasis through its interaction with RTKs. We have developed a CD44v6 peptide which originates from the sequence of CD44v6 and which inhibits tumor growth, blocks metastasis and even eliminates already established metastases of pancreatic cancer. A modified version of this CD44v6 peptide is in clinical trial phase I/Ib (https://clinicaltrials.gov/ct2/show/NCT03009214?term=amcure&rank=1). CD44-G-Protein-Coupled-Receptors: Hyaluronan (HA), the main ligand for CD44 augments CXCL12-induced CXCR4 signaling, a step that is required during angiogenesis. In contrast small HA fragments (sHA) exert the opposite effect. CD44-Wnt signaling: CD44 is involved in the regulation of LRP6 maturation and activation.
The themes developed in the group are:
1) Contribution of CD44 to the tumor microenvironment and to the metastatic niche
CD44 expressed on cancer cells is highly involved in tumor initiation, progression and in the metastatic process. However, a tumor is more than only cancer cells. Activated stromal cells as well as infiltrating immune cells form a tumor microenvironment that is essential for cancer cells proliferation, migration and survival. In pancreatic ductal adenocarcinoma (PDAC), one of the most lethal types of cancer, most of the tumor volume is made up of tumor stroma composed by cancer-associated fibroblasts (CAF), pancreatic stellate cells (PSC; Figure 2), tumor-associated macrophages (TAM) and other immune cells. The difficulties in PDAC treatment can be in part explained by the early dissemination into the liver, where a pre-metastatic niche composed of hematopoietic bone marrow derived cells is already formed. All stromal cells express several CD44 isoforms which might participate in the regulation of molecular pathways involved in the activation of the stroma and in the formation of the metastatic niche. Given the potent impact of CD44 inhibition in PDAC, we are currently investigating its contribution in the stromal compartment on tumor growth and on early dissemination.
Figure 2: Pancreatic tumor expressing CD44v6 and MET (left), CD44 expression in blood vessels from a pancreatic tumor (right)
Figure 3: Pancreatic Stellate Cells expressing CD44 and the activation marker Col1a1.
2) CD44 and HA in chemokine signaling
The interplay between HA, CD44, CXCL12 and CD44 has consequences on the homing of hematopoietic stem cells to their niche and in hematological diseases (chronic lymphocytic leukemia, acute myeloid leukemia). The collaboration between these molecules plays a role in the resistance of leukemic stem cells to chemotherapy.
3) CD44 in Wnt signaling
The molecular mechanism of action of CD44 in Wnt signaling is studied during the development and homeostasis of the intestine and in intestinal stem cell function.
Figure 4. section of a colon and organoid
Given the importance of CD44 in intestinal stemness, the consequences of a removal of CD44 in the intestinal epithelium is investigated in intestinal regeneration.
In addition, the crosstalk between CD44 and Wnt is studied in inflammatory bowel diseases and Wnt-driven colorectal cancer. There, special attention is focused on cancer cell plasticity.
Figure 5: TOP-GFP spheroids
4) The CD44-MET collaboration
We are further characterizing the molecular complex between CD44v6 and MET using advanced microscopy methods.
We are also studying the importance of the CD44v6/MET collaboration in bacterial infection with a specific focus on Listeria Monocytogenes and the involvement of these molecules in meningitis.
Figure 6: Internalization of MET after induction with Internalin B
We have established a Cd44 floxed and a Cd44v6 floxed mouse and study the role of CD44 in development upon conditional activation of Cd44 in liver, intestine, breast and skin. We also have developed a panel of CRISPR/Cas constructs against various CD44 isoforms.