Cell adhesion and cell migration play important roles in variety of physiological and pathological events such as tissue morphogenesis, blood vessel stability, and cancer invasion and metastasis. Integrin is a major family of cell-extracellular matrix adhesion proteins and is essential for both cell adhesiveness and cell motility, while immunoglobulin superfamily (IgSF) proteins typically engage cell-cell adhesion and also regulate cell movement. To understand the interplay of cell adhesion and cell motility, the research in our lab has focused on the roles of cell adhesion proteins and their associated proteins in tumor progression and metastasis, angiogenesis, and tumor-microenvironment interaction. The long-term goal of our lab is to delineate the molecular and cellular mechanisms of cell adhesion and cell migration in tumor progression such as metastatic colonization and in tissue morphogenesis such as angiogenesis by combining both in vitro and in vivo approaches through dissecting the molecular interactions between cell adhesion molecules and cell environments.
We primarily study the tetraspanin proteins, which associate with integrins and IgSF proteins and form tetraspanin-enriched microdomains (TEMs). Tetraspanins belong to a large superfamily and play important roles in various biological functions such as immune response, sperm-egg fusion, viral infection, and neuronal development. Tetraspanins have been found in various species ranging from yeast to human, indicating ancient and essential roles of tetraspanins during the evolution. The molecular and cellular mechanisms by which tetraspanins regulate a variety of biological functions still remain not well understood.
1) Tetraspanin-enriched microdomains, tumor cell movement, and metastatic colonization:
In humans, there are 33 tetraspanins, some of which such as KAI1/CD82 and CD9 suppress tumor progression and metastasis while others such as CD151 and CO-029 promote tumor progression and metastasis. However, the mechanisms remain unclear. Recent studies underscore that tetraspanins have enormous potentials in clinical applications as therapeutic targets, prognostic and diagnostic markers, staging indicator for cancer progression and metastasis.
One of the tetraspanins, KAI1/CD82, has been identified as a caner metastasis suppressor. The initial study of KAI1/CD82 was based on its role in prostate cancer but the following studies demonstrated that KAI1/CD82 is wide-spectrum suppressor for many cancers ranging from breast, cervical, ovarian, skin, liver, gastric, colon, to pancreas cancers. Metastatic cancers are usually accompanied with the loss of KAI1/CD82 expression. The mechanism of KAI1/CD82-mediated metastatic inhibition of cancer remains unclear. We found that the FAK-Src-p130CAS/CrkII-Rac pathway was important for the KAI1/CD82-mediated suppression of cell motility and invasiveness in prostate cancer. We also identified that palmitoylation and transmembrane interaction of KAI1/CD82 is important for its biological activities and that the vesicular trafficking also plays an interesting role in tetraspanin functions. During the KAI1/CD82 study, we discovered a novel transmembrane protein that physically associates with tetraspanins and belongs to the immunoglobulin superfamily (IgSF). This IgSF protein, called EWI2/PGRL, directly inhibits cell motility and is important for KAI1/CD82's activity. We also demonstrated that KAI1/CD82 undergoes the lipid raft-dependent endocytosis and reorganize lipid rafts and tetraspanin-enriched microdomain (TEM) in a cholesterol-dependent manner. Interesting, our recent observations also indicate that KAI1/CD82 also plays an important role in the interaction between tumor cells and their microenvironment. These findings have provided mechanistic insight into the cancer metastasis suppression mediated by KAI1/CD82. We are analyzing the genetically engineered animal models of KAI1/CD82 and EWI2/PGRL, in combination with systems biological approach, to further determine the roles and delineate the mechanisms of these proteins in animal development and cancer progression and metastasis.
2) Tetraspanins, vascular morphogenesis, and vascular stability in contrast to KAI1/CD82, tetraspanin CD151 promotes cell migration. We recently found CD151 regulates cell motility through a novel endocytosis pathway and by regulating the trafficking of its associated integrins. Tetraspanin CD151 is highly expressed in endothelium and required for the postnatal vascular morphogenesis. Although it is well established thatCD151 physically associates with integrins, the mechanism by which CD151 regulatesvascular morphogenesis is basically unknown. We demonstrated that CD151-silenced endothelial cells can still undergo morphogenesis in vitro but the vascular structure cannot be maintained without CD151. In the absence of CD151, the endothelial cells become more retractile, leading to the full disruption of the established vascular structure. Enhanced RhoA and Rho kinase activities and increased myosin light chain phosphorylation appear to be directly responsible for this aberrant retraction and likely result from the decreased Rac1 activity when CD151 is silenced. Inhibitors for Rho kinase or myosin light chain assembly can rescue the deficient angiogenesis in CD151-null mice and aberrant vascular morphogenesis in vitro of CD151-silenced endothelial cells. Together, our study indicate that endothelial CD151 reinforces the integrin-extracellular matrix interaction and cell-cell adhesion to maintain the vascular integrity during vascular morphogenesis.
Narrative of Current Projects in Details
How tetraspanin CD82 inhibits tumor cell movement and tumor progression and metastasis
How tetraspanin CD151 strengthens vascular stability
Stem cell and tissue engineering