Glycosylphosphatidylinositol (GPI) hydrolysis by Transforming Growth Factor-β1 (TGF-β1) as a potential early step in the inhibition of epithelial cell proliferation

Glycosylphosphatidylinositol (GPI) was previously identified in rabbit articular chondrocytes as being a precursor of inositolphosphate glycan (IPG), released upon (Transforming Growth Factor-beta) (TGF-beta) exposure, and capable of mimicking the proliferative effects of the growth factor. Here, using mink lung epithelial cells (CCL 64), which are known to be growth-inhibited by TGF-beta, we studied the potential role of GPI-derived molecules in the antiproliferative effect of TGF-beta 1. We first identified an endogenous pool of GPI material and three different anionic forms of IPG in epithelial cells pre-labeled with [3H] glucosamine. Shortly (8 min) after TGF-beta 1 addition, the cells responded by a rapid and transient hydrolysis of GPI, accompanied by the release of the most anionic form of IPG. This TGF-beta-released IPG, after partial purification, was shown to decrease the proliferation of CCL 64 cells. Moreover, anti-IPG antibodies reduced the effects of TGF-beta and blocked the effects of partially purified IPG. These data strongly suggest that GPI hydrolysis may be an early step of the TGF-beta signalling pathway involved in growth inhibition of epithelial cells.