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TGF-beta blocks early but not late differentiation-specific gene expression and morphologic differentiation of 3T3 T
R L Sparks1, B J Allen, E E Strauss
1Department of Cell Biology and Anatomy, School of Medicine, Oregon Health Sciences University, Portland 97201-3098.
Abstract:
Transforming growth factor-beta (TGF-beta) inhibits morphologic differentiation of BALB/c 3T3 T cells as well as other proadipocyte models. Our prior studies suggested that TGF-beta may act only during the early stages of differentiation induction. However, we did not determine whether TGF-beta was differentially effecting expression of any of the various differentiation-specific genes or if it could cause down-regulation of these genes in differentiated cells. Therefore, in the current study we tested the effects of exogenous TGF-beta (0.01-5.0 ng/ml) on morphologic differentiation and on differentiation-dependent gene expression (Northern and slot blot analyses) at various times during differentiation. When induced to differentiate, 3T3 T cells first undergo predifferentiation growth arrest and from this state molecular, biochemical, and morphological differentiation proceeds. Here it was found that when added prior to the onset of differentiation, TGF-beta was a potent inhibitor or morphologic differentiation as well as of the expression of differentiation-specific genes such as lipoprotein lipase (LPL) and glycerol-3-phosphate dehydrogenase (GPD). However, once morphologic differentiation began, TGF-beta was ineffective in blocking differentiation. In addition, exposure of fully differentiated cells to TGF-beta for up to 72 hours caused no decrease of differentiation-specific genes and even a 7-day treatment caused no morphologic dedifferentiation. Tumor necrosis factor also had no detectable effect on fully differentiated cells.
Insights
Transforming growth factor-beta (TGF-beta) inhibits early cell differentiation and gene expression in 3T3 T cells. However, TGF-beta does not affect cells once differentiation has begun or in fully differentiated cells.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Transforming growth factor-beta (TGF-beta) is known to inhibit the differentiation of proadipocyte models.
- Previous studies suggested TGF-beta's inhibitory effects occur early in differentiation induction.
- The precise timing and impact on specific gene expression remained unclear.
Purpose of the Study:
- To investigate the effects of TGF-beta on morphologic differentiation and gene expression at various time points during differentiation.
- To determine if TGF-beta affects differentiation-specific gene expression or causes down-regulation in differentiated cells.
Main Methods:
- BALB/c 3T3 T cells were treated with varying concentrations of exogenous TGF-beta (0.01-5.0 ng/ml).
- Morphologic differentiation was assessed.
- Differentiation-dependent gene expression was analyzed using Northern and slot blot analyses at different stages of differentiation.
Main Results:
- TGF-beta potently inhibited morphologic differentiation and expression of genes like lipoprotein lipase (LPL) and glycerol-3-phosphate dehydrogenase (GPD) when added before differentiation onset.
- Once morphologic differentiation commenced, TGF-beta was ineffective in blocking further differentiation.
- Fully differentiated cells exposed to TGF-beta for up to 72 hours showed no decrease in differentiation-specific gene expression or morphologic dedifferentiation.
Conclusions:
- TGF-beta's inhibitory effects on 3T3 T cell differentiation are restricted to the early stages, prior to the onset of morphologic differentiation.
- Differentiated cells are refractory to TGF-beta's inhibitory or dedifferentiating effects.
- The timing of TGF-beta exposure is critical for its impact on adipocyte differentiation.