unit 2 week 3 pt 2 Flashcards
How do cells organize themselves within developing organs?
The complex three-dimensional arrangements of cells in developing organs are thought to depend on selective interactions between cells of the same type and different types. Studies of organoids in vitro help researchers understand these processes.
How did early experiments explore cell-cell recognition and adhesion?
Early experiments involved dissociating developing organs from embryos and placing the single cells in culture. Cells from different organs would initially form mixed aggregates but eventually sort themselves, adhering only to cells of the same type, which would then differentiate into structures typical of their original organ.
What role do cell adhesion proteins play in cellular interactions?
There are four major families of integral membrane proteins responsible for cell-cell adhesion: selectins, members of the immunoglobulin superfamily (IgSF), integrins, and cadherins. These proteins mediate cell recognition and adhesion and help cells interact selectively with other cells.
What are the two major functions of adhesion proteins?
Adhesion proteins have two major roles: (1) providing structural support for adhesion between cells and (2) transferring information across the plasma membrane through transmembrane signaling, which influences cellular processes like growth, migration, differentiation, and survival.
How do adhesion proteins transmit signals within the cell?
Proteins like integrins and cadherins transmit signals from the extracellular environment to the cytoplasm by linking with the cytoskeleton and regulatory molecules, such as protein kinases and G proteins. These signals can alter gene expression and affect cell behavior.
What is lymphocyte homing, and how was it studied in the 1960s?
Lymphocyte homing is the phenomenon where lymphocytes return to their original sites after being removed from peripheral lymph nodes, radioactively labeled, and injected back into the body. This process was studied in vitro by allowing lymphocytes to adhere to frozen sections of lymphoid organs, where they selectively adhered to the endothelial lining of venules in peripheral lymph nodes.
What are selectins, and how do they function in cell adhesion?
Selectins are a family of integral membrane glycoproteins that recognize and bind to specific sugar arrangements in oligosaccharides on other cells. There are three known selectins: E-selectin (on endothelial cells), P-selectin (on platelets and endothelial cells), and L-selectin (on leukocytes). They mediate transient interactions between circulating leukocytes and vessel walls at sites of inflammation and clotting, with calcium required for binding.
What role do selectins play in inflammation?
During inflammation, selectins help capture leukocytes, which are flowing quickly through the bloodstream. They mediate the slowing down and rolling of neutrophils along the vessel wall, allowing for the leukocytes to stop at sites of infection or injury.
What is the process of leukocyte adhesion during acute inflammation?
In acute inflammation, venules’ endothelial cells become adhesive to neutrophils in response to chemical signals. Selectins on the endothelial cells cause the neutrophils to roll slowly along the vessel wall. Integrins on neutrophils are then activated, leading to a strong adhesion to the vessel wall.
How can selectins be blocked to reduce inflammation?
Anti-selectin antibodies can block the binding of neutrophils to selectins, preventing neutrophil rolling and reducing inflammation. Synthetic carbohydrates like efomycines can also compete with the ligands on neutrophils, preventing them from interacting with E- and P-selectins.
How do integrins contribute to the inflammatory response?
Integrins on neutrophils are activated by platelet-activating factor (PAF) on endothelial cells, which enhances their binding affinity to IgSF molecules like ICAM-1 and VCAM-1 on endothelial cells. This causes the neutrophils to stop rolling and firmly adhere to the vessel wall, facilitating their movement into the tissue.
What is leukocyte adhesion deficiency (LAD), and how does it affect the inflammatory response?
Leukocyte adhesion deficiency (LAD) is a rare disease where patients lack the ?2 subunit of integrins, which is necessary for leukocytes to adhere to endothelial cells in venules. Without this adhesion, leukocytes cannot exit the bloodstream to fight infection, leading to life-threatening bacterial infections.
What is cancer?
Cancer is a disease in which cells escape the body’s normal growth control mechanisms and proliferate uncontrollably.
How can some cancers be treated easily?
Cancers like certain skin or thyroid cancers can be cured by surgically removing the tumor if the malignant cells remain in a single mass.
Why is cancer such a devastating disease?
Cancer is devastating because malignant cells can leave the primary tumor and spread to other parts of the body through the bloodstream or lymphatic system, forming secondary tumors (metastasis).
What are metastatic cells?
Metastatic cells are cancer cells that spread from the primary tumor and initiate secondary tumors in other parts of the body.
What properties do metastatic cells have?
Metastatic cells are: 1. Less adhesive than other tumor cells, allowing them to break free from the tumor. 2. Able to penetrate barriers like extracellular matrices and basement membranes. 3. Able to survive in and colonize normal tissues.
How can metastatic cells be studied?
Metastatic cells in the bloodstream can be captured in blood samples, allowing researchers to study the tumor’s molecular characteristics, predict aggressiveness, and monitor therapy effectiveness.
Why do only a small fraction of cancer cells that enter the bloodstream form secondary tumors?
Only a small number of cancer cells can successfully invade normal tissues and survive to form secondary tumors, making metastasis a rare and complex process.
How do cancer cells penetrate extracellular matrices?
Cancer cells use matrix metalloproteinases (MMPs) to degrade extracellular matrices, allowing them to migrate through tissues and invade new areas.
What is the role of MMPs in cancer?
MMPs break down the extracellular matrix, facilitating the migration and invasion of cancer cells.
How does the extracellular matrix (ECM) change in cancer?
In cancers like breast cancer, the ECM becomes stiffer and more organized (e.g., increased collagen crosslinking), which promotes cancer cell migration.
What is the role of cell-adhesion molecules in metastasis?
The expression of cell-adhesion molecules, especially E-cadherin, influences metastasis. Loss of E-cadherin reduces cell adhesion, making cancer cells more motile and promoting metastasis.
