TRANSFORMING GROWTH-FACTOR-BETA ENHANCES INTEGRIN EXPRESSION AND TYPE-IV COLLAGENASE SECRETION IN HUMAN MONOCYTES

Transforming growth factor beta (TGF-beta), secreted within an inflammatory site or injected locally, induces leukocyte margination, chemotaxis, and accumulation. In addition to its potent direct chemotactic activity, TGF-beta may promote this leukocyte response by influencing cell surface integrin expression. At picomolar concentrations, TGF-beta increases steady-state mRNA levels for both the alpha5 and the beta1 chain of the fibronectin receptor in human blood monocytes. This increase in gene expression is reflected by selectively enhanced expression of alpha5 (CDw49e), beta1 (CDw29), and also alpha3 (CDw49c) adhesion molecules on the cell surface. Functionally, TGF-beta promotes, in a dose- and time-dependent fashion, monocyte adhesion to type IV collagen, laminin, and fibronectin. Potentially facilitating the movement of monocytes through the extracellular matrix, TGF-beta triggers transcriptional and posttranscriptional regulation of both the 92-kDa and the 72-kDa gelatinase/type IV collagenase. Thus, TGF-beta may play a pivotal role in the early phases of inflammation and repair through its ability to mediate monocyte adhesion, chemotaxis, and enzymatic digestion of extracellular matrix, whereas in chronic lesions, excess TGF-beta may contribute to persistent leukocyte accumulation.