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Signaling events initiated by transforming growth factor-beta 1 that require Gi alpha 1
R Kataoka1, J Sherlock, S M Lanier
1Department of Pharmacology, Medical University of South Carolina, Charleston 29425-2251.
Abstract:
Transforming growth factor-beta 1 (TGF-beta 1) initiates a series of signaling events leading to diverse cell type-specific effects on proliferation and morphology. The multiple effects of TGF-beta 1 are not due to selective expression of receptor subtypes, but rather probably reflect cell-specific expression of downstream components of the particular signaling system. To address this possibility and to identify specific signaling pathways activated by TGF-beta 1, we attempted to restore cell responsiveness to the cytokine by introducing various intracellular signal transducers in NIH-3T3 fibroblasts, a cell line that is minimally responsive to TGF-beta 1. In NIH-3T3 fibroblasts stably transfected with Gi alpha 1 cDNA, TGF-beta 1 induced a reversible morphological transformation that was identical to the effect of this cytokine in indicator cells such as AKR-2B fibroblasts. Gi alpha 1 transfectants also exhibited mitogenic hyperresponsiveness to TGF-beta 1. TGF-beta 1 does not elicit these responses in control nontransfected fibroblasts or cells transfected with the guanine nucleotide-binding protein Go alpha 1. The response to TGF-beta 1 in Gi alpha 1 transfectants is blocked by pertussis toxin and is lost in Gi alpha 1 transfectants that have spontaneously reverted and no longer express Gi alpha 1. These data indicate that the expression of the guanine nucleotide-binding protein Gi alpha 1, normally absent in these cells, confers cell sensitivity to TGF-beta 1.
Insights
Introducing Gi alpha 1 protein restored transforming growth factor-beta 1 (TGF-beta 1) responsiveness in NIH-3T3 cells. This finding highlights Gi alpha 1 as crucial for TGF-beta 1 signaling pathways and cell sensitivity.
Area of Science:
- Cell Biology
- Molecular Signaling
- Biochemistry
Background:
- Transforming growth factor-beta 1 (TGF-beta 1) elicits diverse cellular responses, but the mechanisms underlying cell-specific effects remain unclear.
- These differential responses are likely due to variations in intracellular signaling components rather than receptor expression.
- NIH-3T3 fibroblasts exhibit minimal responsiveness to TGF-beta 1, making them a useful model for studying signaling pathway restoration.
Purpose of the Study:
- To investigate the role of intracellular signal transducers in mediating TGF-beta 1 responses.
- To identify specific downstream components responsible for TGF-beta 1 signaling.
- To restore TGF-beta 1 sensitivity in NIH-3T3 fibroblasts by introducing specific signaling molecules.
Main Methods:
- NIH-3T3 fibroblasts were stably transfected with cDNA encoding Gi alpha 1 or Go alpha 1.
- TGF-beta 1-induced morphological transformation and mitogenic responses were assessed in transfected and control cells.
- The effect of pertussis toxin on TGF-beta 1 responses was evaluated.
- Reversion of Gi alpha 1 expression and its impact on TGF-beta 1 sensitivity were analyzed.
Main Results:
- Stable transfection of NIH-3T3 fibroblasts with Gi alpha 1 cDNA conferred sensitivity to TGF-beta 1, inducing morphological transformation and mitogenic hyperresponsiveness.
- Cells transfected with Go alpha 1 or control cells did not respond to TGF-beta 1.
- The observed responses in Gi alpha 1 transfectants were blocked by pertussis toxin and lost upon reversion of Gi alpha 1 expression.
- These results indicate that Gi alpha 1 is essential for mediating TGF-beta 1 signaling in these cells.
Conclusions:
- The expression of guanine nucleotide-binding protein Gi alpha 1, typically absent in NIH-3T3 cells, is sufficient to restore sensitivity to TGF-beta 1.
- Gi alpha 1 acts as a critical downstream mediator in TGF-beta 1 signaling pathways.
- This study elucidates a key molecular determinant of cell responsiveness to TGF-beta 1, offering insights into differential signaling.