It consists of three polypeptides wound around one another in a triple helix. A bundle of these molecules forms a fibril and fibrils are assembled into fibers.Basal LaminaThe basal lamina is a specialized layer of the extracellular matrix that is present beneath all epithelial tissues and lining of digestive tract , epidermis of skin, and endothelial cells that line blood vessels.Tropical helical structure support epithelial sheetIts role is to provide a structural foundation for epithelial tissues. It is made of several proteins including a type of collagen that provides flexible support to the epithelial sheet and also provides a scaffold on which other proteins are assembled.HemidesmosomesEpithelial cells are firmly anchored to the basal lamina by a version of the desmosome called a hemidesmosome. Integrins are the prominent cell adhesion molecules in hemidesmosomes. Their extracellular domains bind to the extracellular matrix proteins in the basal lamina and their cytoplasmic domains are linked to intermediate filaments of the cytoskeleton.The Extracellular Matrix and CancerFor a malignant cancer cell to metastasize, it must break free from the main tumor and colonize a different site in the body. Metastatic tumor cells have an enhanced ability to adhere to extracellular matrix proteins, especially those in the basal lamina.
In order to metastasize, the cell must enter and leave the blood stream through capillaries or other vessels and Since all blood vessels have a basal lamina, a metastatic tumor cell needs to cross the basal lamina at least twice. Since cells attach to basal lamina proteins by means of integrins, many studies have compared the integrins in metastatic and non-metastatic cells in the search for potential treatment.In laboratory tests, blocking these integrins eliminates the melanoma cell’s ability to cross an artificial basal lamina. Drugs targeting this integrin protein are currently in clinical trialsThe Extracellular Matrix Influence on Cell ShapeCell shape is influenced by the structure of the extracellular matrix as well as by the composition of it.Fibroblasts grown on a two-dimensional matrix attach and are flattened. But when grown in a three-dimensional matrix, they are spindle-shaped and look as they do in vivo.The composition of the extracellular matrix also influences the shape of the cell. Neurons maintained in the absence of the extracellular matrix protein laminin attach but do not take theshape of a typical nerve cell. When laminin is added to the culture, the neurons develop extensions resembling axons and dendrites of normal nerve cells.The Extracellular Matrix Influence on Gene ExpressionJoan Caron hypothesized that a specific protein in the extracellular matrix was responsible for the expression of albumin from liver cells.Caron’s Experiments