Thrombin receptor activation results in calcium signaling and protein kinase C-dependent stimulation of DNA synthesis in HEp-2g laryngeal carcinoma cells.
BACKGROUND
Recently, the expression of the "tethered ligand" thrombin receptor in carcinosarcoma and melanoma cells has been shown. However, the role of the thrombin receptor in tumor cell metabolism still is undefined.


METHODS
In this article, the "tethered ligand" thrombin receptor was identified on human epidermoid carcinoma cells (HEp-2g cell line) by using immunofluorescence studies with a monoclonal antithrombin receptor antibody and radioligand binding. Furthermore, the effects of alpha-thrombin and thrombin receptor activating peptides (TRAP)-6 on calcium mobilization, protein kinase C (PKC) translocation, and DNA synthesis were estimated.


RESULTS
Pharmacologic characterization using [3H]TRAP-6 as a radioligand demonstrated a single class of high affinity binding sites (dissociation constant [KD] = 7.2 +/- 2.2 x 10(-7) M) and a binding capacity of 27 +/- 3.4 fmol/mg protein. The function of these binding sites was demonstrated by alpha-thrombin- and TRAP-6-induced mobilization of free intracellular calcium, and translocation of PKC from cytosol to cell membrane. Moreover, alpha-thrombin and TRAP-6 induced an increase in [3H]thymidine incorporation in HEp-2g cells that could be blocked by the PKC inhibitor bisindolylmaleimide.


CONCLUSIONS
To the authors' knowledge, the results of this study demonstrate for the first time functional thrombin receptors in epidermoid carcinoma cells. The thrombin receptor appears to be involved in growth regulation in HEp-2g cells by a PKC-dependent mechanism.
Kaufmann
R
R
Max Planck Gesellschaft, Research Unit Pharmacological Hemostaseology, Friedrich Schiller University Jena, Germany.
Schafberg
H
H
Rudroff
C
C
Nowak
G
G
D002118:Calcium / Q000378:metabolism*; D002277:Carcinoma / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D004273:DNA, Neoplasm / Q000096:biosynthesis*; D004789:Enzyme Activation; D005455:Fluorescent Antibody Technique; D006801:Humans; D007822:Laryngeal Neoplasms / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D018179:Receptors, Thrombin / Q000378:metabolism*; D015398:Signal Transduction; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D004273:DNA, Neoplasm; D018179:Receptors, Thrombin; D011493:Protein Kinase C; D002118:Calcium