Glycosylphosphatidylinositol-anchored Proteins Regulate Transforming Growth Factor-β Signaling in Human Keratinocytes

• Published in: The Journal of biological chemistry 2003-12, Vol.278 (49), p.49610
• Main Authors: Betty Yuet Ye Tam, Kenneth W. Finnson, Anie Philip
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M308492200

Glycosylphosphatidylinositol (GPI)-anchored proteins have been demonstrated to bind transforming growth factor-β (TGF-β) in certain cell lines. However, the identity of these GPI-anchored proteins and the role they may play in TGF-β signaling remain unknown. We have previously reported the presence of GPI-anchored TGF-β-binding proteins on human skin fibroblasts and keratinocytes (Tam, B. Y. Y., and Philip, A. (1998) J. Cell. Physiol. 176, 553–564; Tam, B. Y. Y., Germain, L., and Philip, A. (1998) J. Cell. Biochem. 70, 573–586). On human keratinocytes, we identified a 150-kDa GPI-anchored TGF-β1-binding protein (r150) and demonstrated that it can form a heteromeric complex with the type I and II TGF-β signaling receptors. To explore whether GPI-anchored proteins modulate TGF-β signaling in keratinocytes, we created keratinocytes defective in GPI anchor biosynthesis (GPI mutant cells) by chemical mutagenesis of HaCaT cells. Mutant clones were selected by fluorescence-activated cell sorting analysis based on the loss of a CD59 marker. In comparison with parental HaCaT cells, GPI mutant cells demonstrated a significant loss of r150 expression. In contrast, the levels of the type I and II TGF-β receptors and their ligand affinities, cell morphology, and doubling time remained unchanged. Importantly, GPI mutant cells displayed enhanced gene transcriptional activity and Smad2 and Smad3 activation in response to TGF-β1 treatment in a dose-dependent manner. Taken together, our results indicate that GPI-anchored protein(s) inhibit TGF-β signaling and implicate r150 as the GPI-anchored protein responsible for this inhibition in human keratinocytes.