DIFFERENT EXPRESSION OF THE ALPHA-2-MACROGLOBULIN RECEPTOR LOW-DENSITY LIPOPROTEIN RECEPTOR-RELATED PROTEIN IN HUMAN KERATINOCYTES AND FIBROBLASTS/

We compared, using a combination of different immunological methods an d by competitive PCR, the expression of the alpha 2-macroglobulin rece ptor/low-density lipoprotein receptor-related protein (alpha 2-M-R/LRP ) in human keratinocytes and fibroblasts. This receptor has previously been found in skin only in dermal cells associated with fibroblasts a nd dendritic cells. For immunodetection we used mouse monoclonal antib odies against the two subunits of the receptor and against the recepto r-associated protein (RAP), known as the regulatory protein of the rec eptor activity. The alpha 2-M-R/LRP was found to be predominantly loca ted intracellularly in keratinocytes whereas a distinct labelling of t he outer membrane surface was found in fibroblasts. RAP is abundant in fibroblasts but is less expressed in keratinocytes. In frozen skin se ctions receptor immunoreactivity was detected in the epidermis with in creased reactivity of basal keratinocytes, as well as in the dermis in association with dermal fibroblasts, By immunoprecipitation of biotin ylated cell extracts, polypeptides were identified corresponding to th e alpha-subunit and beta-subunit of the receptor as well as to the cop recipitating RAP, Competitive PCR revealed the presence of 67.9 and 20 49.7 ag of alpha 2-M-R/LRP mRNA per cell in keratinocytes and fibrobla sts, respectively. The results demonstrate that both cell types expres s alpha-M-R/LRP mRNA and contain receptor protein as well as RAP but i n different quantities and subcellular localizations.