A scientific article by Assist. Prof. Dr. Rasheed M. Rasheed entitled "Cell adhesion molecules and cell ligands"
The ability of cells to adhere through specific interactions plays an important role in a wide range of biological pathways, such as hemostasis (stopping bleeding from injured blood vessels), immune response, and embryogenesis inflammation. Significant advances have been made in our understanding of the molecules that mediate cell adhesion to each other and to proteins in the intercellular matrix. This process is complex, well-regulated, and is involved in embryonic and organ development, immune system function, and vascular integrity. Hence, dysfunction of this process has been associated with a number of disease cases.
Cell adhesion molecules (CAMs) can be defined as a group of cell surface proteins that are involved in the attachment of cells to other cells or to the extracellular matrix in a process called cell adhesion. CAMs help cells stick to each other and to their surroundings. They are important in maintaining tissue structure and function and play a fundamental role in ensuring that organs are able to function normally. Acting as “molecular glue,” CAMs play important roles in cellular mechanisms of growth, inhibition of contact, apoptosis, and a wide range of diseases.
Cell adhesion molecules include several types, depending on their structure, which can be explained as follows:
1. Cadherins: are a type of protein found on the surfaces of living cells and play a fundamental role in cell adhesion that fixes cells within tissues and binds them together. They depend on calcium Ca+2 in their work. There are many types of cadherin molecules, which are distinguished from each other by placing a letter in front of them. Cadherins of the same type can bind to each other. For example, N-cadherin only binds to another N-cadherin, so groups of cells that produce the same type of cadherin molecules tend to stick to each other, while cells that produce different cadherins tend to separate from each other.
2. Selectins: Another family of calcium-dependent cell adhesion proteins, they include three types: E-selectin in endothelial cells, L-selectin in white blood cells, and P-selectin in platelets. Selectins are exclusively involved in cell binding via lectin-glycan interactions.
3. Immunoglobulin super family CAMs (IgSF CAMs): They are a large group of cell surface proteins that participate in cell recognition, binding, or adhesion. The most important members of this group of adhesion proteins are intercellular adhesion molecule 1 (ICAM-1), neural adhesion molecule 1 (NCAM-1), and vascular adhesion molecule 1 (VCAM-1). Their interactions do not depend on calcium. For example, in keratinocyte/leukocyte interactions, type ICAM-1 is very important in initiating inflammatory responses.
4. Integrins: This group is similar to the (IgSF CAMs) group in that it does not require calcium for its function. The main difference between it and the rest of the types of cell adhesion proteins is that it mediates the adhesion of cells to the extracellular matrix. Cells receive many signals through integrins such as cell growth, division and differentiation in addition to their important role in the process of programmed cell death. White blood cells express many integrins that play particularly important roles in immune cells.
The connection of cells in multicellular organisms by cell adhesion molecules leads to the emergence of what are known as cell junctions, which can be classified into several types, which are:
1. Occluding junctions (tight junctions): which close the gaps between cells, forming an impermeable barrier to passage. Closed junctions are usually found in epithelial and endothelial tissues, where they close the gaps and regulate the intercellular transport of solutes and extracellular fluids in these tissues that act as barriers.
2. Anchoring junctions: which maintain cell cohesion and strengthen communication between cells. They can be divided into three types:
A- Adherens junctions: They are a type of cell connections that are constantly assembled and disassembled, which enables tissue cells to respond to biochemical signals and changes in their microenvironment. This type provides a strong bond between adjacent cell membranes.
B- Desmosomes: It is the strongest type of cell adhesion to each other, and is found in many tissues such as cardiac muscle tissue, bladder, intestinal mucosa and all tissues exposed to violent mechanical pressures. A malfunction in the work of this type of communication can cause cardiac arrhythmia in the right ventricle, and its symptoms are fainting, shortness of breath, and heart palpitations.
C- Hemidesmosomes: Very small protein molecules that resemble spikes found in the skin epidermis cells and that are linked to the intercellular matrix. Some genetic or acquired diseases that are accompanied by a defect in the components of these links cause skin ulcers between the different layers of the skin that appear in the form of a group of symptoms including weak skin, blisters, and others.
3. Gap junctions: These are a group of channels that connect cells and allow direct transport of ions and small molecules between them. They are found in almost all cells in solid tissues. They connect the cytoplasm of adjacent cells, allowing molecules to be transported between cells. These channels are called connexons, which are made up of membrane proteins called connexins. They are continuous channels when they touch and conform to each other in adjacent cells.
The development of our understanding of the precise structure of cell adhesion molecules and their functional roles contributes greatly to understanding the mechanism of occurrence and development of many health problems that humans and other living organisms are exposed to due to their importance in stabilizing the internal environment and regulating communication processes between cells and the development and differentiation of cells, in addition to their very important role in the immune response and combating many serious diseases such as tumors of various types.
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