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| Author(s): |
Tamara da Rocha Machado Ferreira
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ) |
| Defense date: | 2012-10-09 |
| Examining board members: |
Anamaria Aranha Camargo;
Daniela Sanchez Bassères;
Leticia Labriola;
Enrique Mario Boccardo Pierulivo;
Bryan Eric Strauss
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| Advisor: | Anamaria Aranha Camargo; Erico Tosoni Costa |
| Abstract | |
The ADAM23 gene is epigenetically silenced in breast tumors of more advanced stages and its silencing in these tumors gives the patient a greater risk of developing metastasis and a worse prognosis. The ADAM23 gene silencing in the MDA-MB-435 breast tumor cell line reduces the proliferative capacity and increases migratory and invasive abilities of cells in three-dimensional culture models. Yet, paradoxically, the ADAM23 gene silencing in this line reduces tumorigenic and metastatic abilities of cells in in vivo assays using immunodeficient animals. Subsequent tests using ADAM23 positive and negative cells mixtures revealed that negative cells stimulate proliferation, migration and invasion of positive cells and the heterogeneity of ADAM23 expression in tumors is important for the spreading and metastatic colonization. This study aimed to validate the association between ADAM23 gene silencing in primary tumors and tumor progression as well as find an alternative cellular model for performing functional tests to prove the role of the ADAM23 gene in proliferation, migration and cell invasion, and to prove the existence of cell interaction between ADAM23 positive and negative cells. The analysis of ADAM23 gene expression in samples from different stages of gliomas by RT-PCR revealed that the expression of this gene decreases over tumor progression and is greatly reduced in tumors of advanced degree. However, unlike that observed in breast tumors, the ADAM23 gene silencing in gliomas is not caused by hypermethylation of its promoter region or by mutations in its coding region, or by loss of heterozygosity. Unfortunately, it was not possible to select clones derived from the U87MG glioblastoma cell line with stable silencing of the gene ADAM23 for the functional testing. Apparently, the silencing of ADAM23 in this cell line results in cell cycle arrest in G0/G1 phase, preventing the selection of clones with stable gene silencing. The same phenomenon was not observed in SKmel-37 melanoma cell line, allowing selection of clones with stable silencing of ADAM23 and functional testing. Monolayer proliferation curves and in vitro MTT incorporation assays in three-dimensional models showed that ADAM23 silencing in the SKmel-37 cell line reduces their rate of proliferation by 20-50%. Flow cytometry assays demonstrated that ADAM23 silencing interferes with the expression of αvβ3 and αvβ5 integrins in the cell membrane, resulting in a 50% decrease in binding afinity to the matrix and a significant increase in migratory and invasive abilities on collagen. In vitro and in vivo assays using ADAM23 positive and negative SKmel-37 cell mixtures also confirmed the existence of interaction between the two cell subsets. In vitro invasion and migration on collagen assays revealed that ADAM23 negative cells induce migration and invasion of positive cells. Furthermore, in in vivo tumorigenic tests we found that tumors formed from injection of a mixture of positive and negative cells exhibit growth similar to the tumors formed after injection of ADAM23 positive cells. (AU) | |