Laminin and bullous pemphigoid antigen are distinct basement membrane proteins synthesized by epidermal cells

Abstract

We sought to determine if laminin, a high molecular weight glycoprotein of basement membrane, is synthesized by epidermal cells and whether it is distinct from bullous pemphigoid (BP) antigen, another high molecular weight-protein of basement membrane. By indirect immunofluorescence we detected laminin in cultures of Pam cells (a mouse keratinocyte cell line) and normal human epidermal cells. To directly demonstrate its biosynthesis, we labeled the cells with radioactive amino acids and then extracted the cell layers with nonionic detergent. Using immunoprecipitation followed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and fluorography to identify radiolabeled laminin, we could precipitate the 2 chains of laminin from cell culture medium and extracts of the cell layers. BP antigen, immunoprecipitated from the cells, did not comigrate with laminin on SDS-PAGE. In addition, BP antigen could be immunoprecipitated from cell extracts depleted of laminin, and conversely, laminin could be immunoprecipitated from cell extracts depleted of BP. We conclude that laminin is synthesized by epidermal cells (specifically, keratinocytes) and is distinct from BP antigen.