TGF-beta receptor expression on human keratinocytes: a 150 kDa GPI-anchored TGF-beta1 binding protein forms a heteromeric complex with type I and type II receptors.
Keratinocytes play a critical role in re-epithelialization during wound healing, and alterations in keratinocyte proliferation and function are associated with the development of various skin diseases. Although it is well documented that TGF-beta has profound effects on keratinocyte growth and function, there is a paucity of information on the types, isoform specificity and complex formation of TGF-beta receptors on keratinocytes. Here, we report that in addition to the types I, II, and III TGF-beta receptors, early passage adult and neonatal human keratinocytes display a cell surface glycosylphosphatidylinositol (GPI)-anchored 150 kDa TGF-beta1 binding protein. The identities of the four proteins were confirmed on the basis of their affinity for TGF-beta isoforms, immunoprecipitation with specific anti-receptor antibodies, sensitivity to phosphatidylinositol specific phospholipase C and dithiothreitol, and 2-dimensional electrophoresis. Interestingly, the antitype I TGF-beta receptor antibody immunoprecipitated not only the type I receptor, but also the type II receptor and the 150 kDa component, suggesting that the 150 kDa component form heteromeric complexes with the signalling receptors. In addition, two-dimensional (nonreducing/reducing) electrophoresis confirmed the occurrence of a heterotrimeric complex consisting of the 150 kDa TGF-beta1 binding protein, the type II receptor, and the type I receptor. This technique also demonstrated the occurrence of types I and II heterodimers and type I homodimers of TGF-beta receptors on keratinocytes, supporting the heterotetrameric model of TGF-beta signalling proposed using mutant cells and cells transfected to overexpress these receptors. The keratinocytes responded to TGF-beta by markedly downregulating all four TGF-beta binding proteins and by potently inhibiting DNA synthesis. The demonstration that the 150 kDa GPI-anchored TGF-beta1 binding protein forms a heteromeric complex with the TGF-beta signalling receptors suggests that this GPI-anchored protein may modify TGF-beta signalling in human keratinocytes.
Montreal General Hospital and Department of Surgery, McGill University, Quebec, Canada.
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Tam
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Germain
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Philip
D000328:Adult; D001704:Biopolymers; D002478:Cells, Cultured; D004229:Dithiothreitol / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D017261:Glycosylphosphatidylinositols / Q000378:metabolism*; D006801:Humans; D007231:Infant, Newborn; D015603:Keratinocytes / Q000378:metabolism*; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D054801:Phosphoinositide Phospholipase C; D011233:Precipitin Tests; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism*; D015398:Signal Transduction; D016212:Transforming Growth Factor beta / Q000378:metabolism; D010738:Type C Phospholipases / Q000378:metabolism
D001704:Biopolymers; D017261:Glycosylphosphatidylinositols; D018125:Receptors, Transforming Growth Factor beta; D016212:Transforming Growth Factor beta; D010738:Type C Phospholipases; D054801:Phosphoinositide Phospholipase C; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D004229:Dithiothreitol