Human alpha-thrombin stimulates proliferation of interferon-gamma differentiated, growth-arrested U937 cells, overcoming differentiation-related changes in expression of p21CIP1/WAF1 and cyclin D1.
In addition to its central role in blood coagulation and hemostasis, human alpha-thrombin is a growth factor for a variety of cell types. We recently demonstrated that interferon-gamma (IFNgamma)-differentiated U937 cells show increased expression of the proteolytically activated receptor for thrombin (PAR-1) relative to undifferentiated U937. In the present study we show that cell proliferation is inhibited in IFNgamma-differentiated cells relative to undifferentiated U937. Addition of thrombin to the differentiated cells, however, overcomes the inhibition and restores the cells to a highly proliferative state. Ribonuclease protection assays indicate that the IFNgamma-induced growth arrest is associated with an increased expression of the cyclin-dependent kinase inhibitor p21(CIP1/WAF1) and downregulation of cyclin D(1). Treatment of cells with thrombin downregulates p21(CIP1/WAF1) expression in these cells and upregulates cyclin D(1) mRNA expression, thus overcoming the differentiation-related effects in a coordinated manner. Treating differentiated cells with the PAR-1 activation peptide, SFLLRN, stimulates proliferation and has effects similar to those of thrombin on expression of p21(CIP1/WAF1). Thus, it appears that these thrombin stimulated proliferative effects are mediated through activation of PAR-1. These results may help explain how thrombin can overcome growth arrest in normal tissue to initiate tissue repair and why thrombin and thrombin-like enzymes may contribute to unrestricted proliferation observed in certain malignancies.
Naldini
Antonella
A
Institute of General Physiology, University of Siena, Siena, Italy. Naldini@Unisi.it
Carney
Darrell H
DH
Pucci
Annalisa
A
Carraro
Fabio
F
D002453:Cell Cycle / Q000187:drug effects*; D002454:Cell Differentiation / Q000502:physiology; D002455:Cell Division / Q000187:drug effects; D019938:Cyclin D1 / Q000378:metabolism*; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism*; D015536:Down-Regulation / Q000187:drug effects; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology; D010447:Peptide Hydrolases / Q000378:metabolism; D044463:Receptor, PAR-1; D018179:Receptors, Thrombin / Q000502:physiology; D013917:Thrombin / Q000494:pharmacology*; D020298:U937 Cells / Q000473:pathology*; D015854:Up-Regulation / Q000187:drug effects
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D010446:Peptide Fragments; D044463:Receptor, PAR-1; D018179:Receptors, Thrombin; C082835:thrombin receptor peptide (42-47); D019938:Cyclin D1; D007371:Interferon-gamma; D010447:Peptide Hydrolases; D013917:Thrombin