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Functional characterization of transforming growth factor beta type II receptor mutants in human cancer
1Department of Medicine and Yale Cancer Center, Yale University School of Medicine, New Haven, Connecticut 06520-8032, USA.
Abstract:
We recently identified missense mutations at amino acid residues 526 and 537 located within the highly conserved subdomain XI of the transforming growth factor beta type II receptor (TbetaR-II) serine-threonine kinase in two human squamous carcinoma cell lines. These cell lines are resistant to transforming growth factor beta-mediated inhibition of growth. Moreover, treatment with transforming growth factor beta fails to increase the levels of type 1 plasminogen activator inhibitor and fibronectin synthesis. To test the effects of the mutations on receptor function, mutant TbetaR-II cDNAs were expressed in TbetaR-II-deficient T47D cells. Cyclin A promoter activity was reduced by 50% in cells expressing wild-type TbetaR-II but increased 2-fold in cells transfected with either of the two mutant receptors. Conversely, plasminogen activator inhibitor type 1 promoter activity was increased 6-fold in cells transfected with wild-type receptor but not with either of the two mutant receptors. Moreover, the activity of both mutant serine-threonine kinases was strongly reduced compared to that of the wild-type receptor. Thus, the amino acid residues at positions 526 and 537 seem to be essential for kinase function and signaling activity of the TbetaR-II.
Insights
Missense mutations in transforming growth factor beta type II receptor (TbetaR-II) subdomain XI impair its kinase function. These TbetaR-II mutations confer resistance to growth inhibition and disrupt downstream signaling in squamous carcinoma cells.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Transforming growth factor beta (TGF-β) signaling is crucial for regulating cell growth and differentiation.
- Dysregulation of TGF-β signaling, particularly involving the type II receptor (TbetaR-II), is implicated in various cancers, including squamous cell carcinoma.
- Missense mutations in conserved regions of TbetaR-II can lead to altered receptor function and contribute to tumorigenesis.
Purpose of the Study:
- To investigate the functional consequences of missense mutations at amino acid residues 526 and 537 in subdomain XI of the TbetaR-II serine-threonine kinase.
- To determine the impact of these mutations on TGF-β-mediated growth inhibition and downstream gene expression.
- To elucidate the role of these specific residues in TbetaR-II kinase activity and signaling.
Main Methods:
- Identification of missense mutations in TbetaR-II subdomain XI in human squamous carcinoma cell lines.
- Expression of wild-type and mutant TbetaR-II cDNAs in TbetaR-II-deficient T47D cells.
- Assays to measure Cyclin A and plasminogen activator inhibitor type 1 (PAI-1) promoter activity.
- Assessment of TbetaR-II serine-threonine kinase activity in cells expressing wild-type and mutant receptors.
Main Results:
- Squamous carcinoma cell lines with TbetaR-II mutations at residues 526 and 537 exhibited resistance to TGF-β-mediated growth inhibition.
- Mutant TbetaR-II receptors failed to induce PAI-1 and fibronectin synthesis upon TGF-β treatment.
- Expression of mutant TbetaR-II led to increased Cyclin A promoter activity, contrasting with the inhibitory effect of wild-type TbetaR-II.
- Kinase activity of mutant TbetaR-II was significantly reduced compared to wild-type TbetaR-II.
Conclusions:
- Amino acid residues 526 and 537 in TbetaR-II subdomain XI are essential for its kinase function.
- These mutations disrupt TGF-β signaling pathways, leading to impaired growth inhibition and altered gene expression.
- The identified mutations contribute to the oncogenic phenotype by compromising TbetaR-II's tumor-suppressive activities.