MESSAGE OF NEXIN-1, A SERINE-PROTEASE INHIBITOR, IS ACCUMULATED IN THE FOLLICULAR PAPILLA DURING ANAGEN OF THE HAIR CYCLE

A group of specialized mesenchymal cells located at the root of the ma mmalian hair follicle, known as the follicular or dermal papillary cel ls, are involved in regulating the hair cycle, during which keratinocy tes of the lower follicle undergo proliferation, degeneration and regr owth. Using the arbitrarily primed-PCR approach, we have identified a 1.3 kb messenger RNA that is present in large quantities in cultured r at follicular papillary cells, but not in skin fibroblasts, This mRNA encodes nexin 1, a potent protease inhibitor that can inactivate sever al growth-modulating serine proteases including thrombin, urokinase an d tissue plasminogen activator, In situ hybridization showed that nexi n 1 message is accumulated in the follicular papilla cells of anagen f ollicles, but is undetectable in keratinocytes or other skin mesenchym al cells, In addition, nexin 1 message level varies widely among sever al immortalized rat vibrissa papillary cell lines, and these levels co rrelate well with the reported abilities of these cell lines to suppor t in vivo follicular reconstitution, These results suggest a possible role of nexin 1 in regulating hair follicular growth.