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Mutant p53 tumor suppressor gene causes resistance to transforming growth factor beta 1 in murine keratinocytes
M Reiss1, V F Vellucci, Z L Zhou
1Department of Medicine, Yale University School of Medicine, New Haven, Connecticut 06510.
Abstract:
Human carcinoma cell lines are frequently refractory to the antiproliferative effect of the autocrine growth inhibitor transforming growth factor beta 1 (TGF-beta 1) and often express mutant forms of the tumor suppressor gene p53. Therefore, we wished to determine whether mutant p53 affects the cellular response to TGF-beta 1. A murine p53 complementary DNA carrying an activating point mutation was introduced into TGF-beta 1-sensitive BALB/MK mouse epidermal keratinocytes by retroviral infection. Mp53 transformed cells displayed a spindle-type morphology and expressed between 0.02 and 0.7 ng of mutant p53/mg total protein. Furthermore, whereas TGF-beta 1 caused approximately 90% maximal inhibition of DNA synthesis of parental BALB/MK cells, the Mp53 transformants were inhibited by less than 70%. The median inhibiting dose of TGF-beta 1 was 4.07 +/- 1 (SE) pM for BALB/MK cells, but ranged from 2.4 to 11.2 pM and from 11.7 to 40 pM for two different sets of Mp53 transformants, and increased as a function of the amounts of mutant p53 protein that were expressed. Our findings suggest that mutant forms of p53 inhibit the antiproliferative effect of TGF-beta 1 by interfering with its signaling pathway.
Insights
Mutant p53 interferes with transforming growth factor beta 1 (TGF-beta 1) signaling, reducing its antiproliferative effects in carcinoma cells. This suggests a link between p53 mutations and resistance to TGF-beta 1 in cancer.
Area of Science:
- Oncology
- Molecular Biology
- Cell Biology
Background:
- Human carcinoma cells often resist the growth-inhibiting effects of transforming growth factor beta 1 (TGF-beta 1).
- Mutations in the p53 tumor suppressor gene are common in these refractory cancer cells.
Purpose of the Study:
- To investigate if mutant p53 influences the cellular response to TGF-beta 1.
- To understand the mechanism by which p53 mutations might affect TGF-beta 1 sensitivity.
Main Methods:
- Introduced a mutated murine p53 complementary DNA into TGF-beta 1-sensitive mouse epidermal keratinocytes using retroviral infection.
- Quantified mutant p53 protein expression in the transformed cells.
- Assessed the inhibitory effect of TGF-beta 1 on DNA synthesis in both parental and mutant p53-expressing cells.
Main Results:
- Cells expressing mutant p53 (Mp53 transformants) exhibited altered morphology and varying levels of mutant p53 protein.
- TGF-beta 1 induced less than 70% inhibition of DNA synthesis in Mp53 transformants, compared to approximately 90% in parental cells.
- The median inhibitory dose of TGF-beta 1 increased with higher expression levels of mutant p53 protein.
Conclusions:
- Mutant p53 appears to interfere with the antiproliferative signaling pathway of TGF-beta 1.
- This interference may contribute to the resistance of carcinoma cells to TGF-beta 1's inhibitory effects.