POSSIBLE ROLE OF OSTEOPONTIN IN DEPOSITION OF CALCIUM-PHOSPHATE IN HUMAN PILOMATRICOMAS

Human pilomatricomas are benign epidermal appendage tumors composed of hair matrix-like basaloid cells and keratinized remnant cells referre d to as shadow cells. Deposition of calcium phosphate usually occurs i n the shadow cell nests. Because osteopontin is believed to be involve d in the deposition of calcium phosphate in bones, we asked whether os teopontin messenger RNA also is expressed in pilomatricomas. Using Nor thern blotting and in sits hybridization we detected osteopontin messe nger RNA in pilomatricoma tissues but not in normal skin tissue. By th e combination of in situ hybridization and immunohistochemistry, osteo pontin messenger RNA-expressing cells were identified as CD68-positive macrophages surrounding the shadow cell nests, Immunohistochemistry o f anti-human osteopontin antibodies revealed that the localization of osteopontin protein was consistent with that of calcium phosphate. The present results suggest that osteopontin produced by macrophages may play a significant role in the deposition of calcium phosphate in the shadow cell nests of pilomatricomas.