The tranforming growth factor β (TGF-β ) family of cytokines participates in regulating cell growth, morphogenesis, and differentiation by modulating expression of a variety of genes (1 –4 ). These gene products broadly cover proteins involved in deposition of an extracellular matrix (ECM), such as fibronectin and its receptor, collagen and collagenase (5 –9 ), the proto-oncogene products c-Jun and JunB (10 –12 ), the cell-cycle regulators p15 and p21 /Waf/Cip (13 –15 ), and proteins involved in apoptotic cell death, such as clusterin (16 ).
