Expression of Hard α-Keratins in Pilomatrixoma, Craniopharyngioma, and Calcifying Odontogenic Cyst

To examine the properties of shadow and ghost cells, 3 kinds of antibodies were raised against human hair proteins and their immunoreactivity was examined in tumors expressing those cells: pilomatrixoma, 14 cases; craniopharyngioma, 17 cases; and calcifying odontogenic cyst (COC), 14 cases. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis and Western blot analyses demonstrated that 2 polyclonal antibodies, PA-HP1 and PA-HP 2, reacted strongly with type I acidic and type II neutral/basic hard α-keratins. The other monoclonal antibody, MA-HP1, reacted with type II neutral/basic hard α-keratins. Immunohistochemical examination revealed that all 3 antibodies reacted only with the hair shaft in sections of normal skin and dermoid cyst. In all pilomatrixoma cases, 3 antibodies reacted with the cytoplasm of transitional and shadow cells but not with that of basophilic cells. Positive reactions were found only in shadow cells of all 13 adamantinomatous craniopharyngiomas. In all COCs, the antibodies reacted only with ghost cells, not with other epithelial components. Immunoreactivity for phosphothreonine, detected in hard α-keratins, also was found in transitional, shadow, and ghost cells. The appearance of shadow or ghost cells might represent differentiation into hair in these 3 kinds of tumors. In pilomatrixoma, a common benign tumor with hair matrix cell differentiation, tumor nests are composed of basophilic, transitional, and shadow cells, corresponding to the epithelial components of mature hair follicles.1 The appearance of shadow cells in the tumor might represent the endpoint of hard keratinization of matrix cells into hair cortex.1,2 There are 2 other tumors displaying shadow cells or their analogue, ghost cells: craniopharyngioma of the pituitary gland3,4 and calcifying odontogenic cyst (COC) of the jaw.5 Recent studies have documented the similarity of the accumulation and alteration of β-catenin in these 3 types of tumors, suggesting an important role of activation of the Wnt-βcatenin-TCF-Lef (T-cell factor/lymphoid enhancer factor) pathway in the pathogenesis of these tumors.6-10 It has been reported that this activated pathway induces differentiation to hair shafts.8-14 Cribier et al2 demonstrated the expression of messenger RNA for human hair keratin basic 1 in transitional cells by in situ hybridization and suggested that the expression of hard keratins in transitional cells might resemble the maturation process of the hair shaft. Tateyama et al15 demonstrated immunohistochemically the expression of human hard α-keratins in shadow cells of adamantinomatous craniopharyngioma and proposed that this tumor might show hair follicle differentiation. Although there have been no English-language articles on the expression of hard α-keratins in ghost cells, melanin pigmentation as seen in cortex cells of the normal hair shaft occasionally is observed in some COC cases.16,17 These findings suggest that differentiation into hair occurs in COC. To examine the properties of shadow and ghost cells in pilomatrixoma, craniopharyngioma, and COC, 2 polyclonal antibodies and 1 monoclonal antibody were raised against human hair proteins, and their immunoreactivity was tested on