EXPRESSION OF TRANSGLUTAMINASE-1 IN HUMAN EPIDERMIS

To explore the expression and function of the membrane-associated or t ype I transglutaminase (TGase1) in human epidermis, we have made a new antihuman TGase1 antibody in goats elicited against a purified active recombinant protein expressed in bacteria, By use of Western blotting and immunoprecipitation methods, the antibody reacted with high speci ficity with only the TGase1 activity of the epidermis and in cultured keratinocytes, By indirect immunofluorescence, the antibody decorated the entire epidermis, including the basal layer, with some potentiatio n of the granular layer, However, these staining properties are quite different from those of a widely used, commercially available TGase1 m onoclonal antibody (termed B.C1), which decorates the granular layers of the epidermis, By Western blotting, it identifies the TGase1 protei n band only weakly, but recognizes strongly a group of bands of 15-20 kDa, two of which by amino acid analysis and amino acid sequencing are the small proline-rich (SPR) 1 and SPR2 proteins, also expressed in e pidermal and epithelial tissues, Together with a series of blocking ex periments with TGase1 proteins and synthetic peptides, these data reve al that the major epitope of the B.C1 antibody most likely resides on the amino-terminus of these two SPR proteins rather than on TGase1. Fu rther studies will now be necessary to determine the role(s) of TGase1 during the different stages of development and differentiation in the epidermis.