Intermediate Filament Proteins Diagnostic Markers in Tumour Pathology

Intermediate filaments (IFS) are cytoplasmic, filamentous structures (8 to 12 nm in diameter) that are present in almost all vertebrate cells. By molecular and biochemical criteria the proteins forming these IFS can be divided into six different IF types which are expressed in characteristic cell-type-dependent patterns. In general, epithelial cells contain cytokeratin IFS. Vimentin IFS are the typical IFS of most mesenchymal cells and tissues; the hallmark IF protein of most muscle cells is desmin; astrocytes of the glia of nervous tissues contain glial filaments made up of glial fibrillary protein (GFP); and neurons are characterised by neurofilaments (NF). Certain neuronal cells have IFS containing peripherin. Some cells and tissues are characterised by specific combinations of more than one type of IF protein. The application of sensitive antibodies, specific for the individual IF proteins, as well as biochemical analyses, including amino acid sequence determinations, has allowed the characterisation and identification of a given cell type by its specific IF protein complement. As the cell-type-specific IF expression is usually maintained after malignant transformation, IF protein typing has become a useful aid in cell classification and histopathological diagnosis, especially in those cases that are difficult to diagnose by conventional techniques because of their indistinct morphology. In addition, the determination of the cells' IF protein complement and possible changes of their expression during transformation can help in understanding the biological principles leading to tumour growth and metastasis.