Upregulation of Class II β-Tubulin Expression in Differentiating Keratinocytes

The diverse functions of microtubules (MT) in different cells and tissues may be facilitated by compositional changes in tubulin isotypes. We obtained partial cDNA clones of class II β-tubulin from a library of differentiating normal human epidermal keratinocytes (NHEK) cells, whereas screening via subtractive hybridization for genes involved in calcium-induced keratinocyte differentiation. Analysis of the isotypic composition of β-tubulin from NHEK cells revealed elevations in class II β-tubulin concentrations at both protein and message levels during cell differentiation, resulting in increased rates of incorporation of class II β-tubulin into MT. Immunohistochemistry of normal and pathologic skin tissues showed that class II β-tubulin occurred in the granular layer of the epidermis and in differentiated areas of carcinomas. Class II β-tubulin was, however, not observed in the uppermost granular and cornified layers of normal epidermis. Further experiments showed that MT were likely to decay in the final stage of terminal differentiation during formation of the cornified envelope. Our results suggest that there is differential modulation of MT composition and stability during keratinocyte differentiation.