Distribution and potential biologic function of the thrombin receptor PAR-1 on human keratinocytes

Abstract

Thrombin has recently been shown not only to exert procoagulant activities, but also to induce mitogenic responses of different cell types involved in wound healing via binding to and cleavage of the thrombin receptor. In order to further explore these aspects of thrombin function, human keratinocytes (HaCaT cell line) were examined for their potential mitogenic responsiveness to thrombin and for the dependency of this process on the expression of the high-affinity thrombin receptor. Quiescent keratinocytes were stimulated in the mitogenic assay with alpha-thrombin and the thrombin receptor activating peptides TRAP42-55 (SFLLRNPNDKYEPY) and TRAP42-46 (SFLLR). A strong induction of cell proliferation was noted with alpha-thrombin, TRAP42-55 and TRAP42-46, but not with the "scrambled" peptide (FSLLR). These findings confirm that keratinocytes express the thrombin receptor and that the sequence of the first two amino acids of the generated neo-N-terminus are important for the activation of the receptor. Using cDNA fragments of the 5' coding sequence of the receptor, Northern blot analysis confirmed that HaCaT keratinocytes express the thrombin receptor. Expression of the receptor was also detected on normal human keratinocytes by immunohistochemistry and in situ hybridization. These data demonstrate the expression and biologic function of the human thrombin receptor on human keratinocytes, suggesting that thrombin, among other mediators, plays an important part in the orchestration of epidermal growth and repair processes.

Mast cell chymase is increased in chronic atopic dermatitis but not in psoriasis

“…An increased number of mast cells containing chymase was observed in the dermis of lesional (a) and non-lesional (b) AD skin in comparison to the non-atopic, non-psoriatic control (c) as well as lesional (d) and non-lesional (e) psoriatic skin (ABC/AP method, original magnification ·100). In lesional AD skin immunoreactivity for MCC was mainly localized around the superficial dermal vascular plexus (g) and, although less pronounced, along the dermoepidermal junction zone (f) (ABC/AP method, original magnification ·400) motrypsin-like proteinases can modify proteinase-activated receptors, which are present on keratinocytes and are thought to be involved in epidermal growth and repair processes [16,17]. Although the precise effects of MCC on keratinocytes in AD still remain to be elucidated, MCC may participate in the events leading to skin barrier dysfunction and dry skin.…”

Thrombin and Phenotypic Modulation of the Endothelium

“…Thrombin receptors are present on many different cell types, including endothelial cells, platelets, VSMCs, 96 -100 fibroblasts, 93,101,102 mast cells, 103,104 macrophages, 104 microglia, 105 tumor cells, keratinocytes, 106 and leukocytes. 107,108 Thrombin signaling varies between cell types.…”

Epidermal growth factor and thrombin induced proliferation of immortalized human keratinocytes is coupled to the synthesis of Egr‐1, a zinc finger transcriptional regulator

“…Moreover, platelets are stimulated by thrombin to aggregation and secretion. In addition, thrombin functions as a mitogen for several cell types, including smooth muscle cells, ®broblasts, and keratinocytes [Shapiro et al, 1996;Balmanno and Cook, 1999;Algermissen et al, 2000]. Thrombin binds to seven-transmembrane-spanning G-protein coupled receptors termed protease activated receptors (PARs).…”