Intermediate filaments, keratins comprising

The keratin family of proteins comprises two of the six classes of intermediate filament proteins found in the cytosol of eukaryotic cells. They provide the intracellular structural stability that complements the intercellular mechanical cohesion provided by desmosomes. Keratin filaments cross the entire cytosol of keratinocytes and their ends are tightly attached to desmosomes by desmoplakin (Fig. 5.9) or, in basal cells, to the related plakin (BP230) and plectin proteins in hemidesmosomes. 

Five classes of intermediate filament proteins have been described, generally referred to as types I through V. Types I and II are the acidic and basic polypeptides, respectively, which comprise the keratins and cytokeratins, a family of heteropolymers that are abundant in epithelia. Type III consist of vimentin, desmin, glial fibrillary acidic protein, and peripherin. Of these, desmin has specific importance... 

The soft epithelial keratin intermediate filaments comprise approximately 20 different keratin polypeptides. " The polypeptides, numbered 1 through 20, comprise type II (basic) keratins and type I (acidic) keratins (Table 8.2). This family of intermediate filaments is crucial in diagnostic IHC for the identification of carcinomatous differentiation and for identification of specific carcinoma subtypes. 

Intermediate filament protein types 1 and 11 are acidic keratin and basic keratin, found in epithelial cells. Vimentin, desmin, glial fibrillary acidic protein, synemin, and peripherin comprise the type 111 intermediate filaments. The type IV intermediate filaments include nestin and syncoilin, which are located in nervous systems and mostly found in neurons. The nuclear intermediate filaments, lamin A, its splice variant lamin C, and lamin B1 and B2 (type V), form a filamentous support inside the inner nuclear membrane [50]. 

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