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| Author(s): |
Sabrina Daniela da Silva
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Faculdade de Odontologia de Piracicaba |
| Defense date: | 2007-06-15 |
| Examining board members: |
Edgard Graner;
Alvimar Lima de Castro;
Fernando Augusto Soares;
Luiz Paulo Kowalski;
Ricardo Della Coletta
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| Advisor: | Edgard Graner; Dirce Maria Carraro |
| Abstract | |
The ubiquitin (Ub)-proteasome pathway controls cellular protein turnover by degrading targeted intracellular proteins tagged with Ub. Graner et al. (2004) demonstrated that the deubiquitinating enzyme USP2a stabilizes and rescues fatty acid synthase (FAS) from proteassomal degradation. FAS plays a central role in de novo lipogenesis and is down-regulated in most of the tissues, because cells preferentially use circulating dietary fatty acids for the synthesis of new structural lipids. On the other hand, it has been demonstrated that FAS is highly expressed in several human cancers and in some of them its expression is correlated with poor outcome. Few studies describe FAS expression in oral squamous cell carcinoma (SCC), however, all of them suggest that the it is increased at the early stages of malignant transformation. It has been shown that FAS is over-expressed in human oral SCC cell lines and plays an essential role in their proliferation. However, the basic mechanism underlying the control of FAS expression in malignant cells is not known at the moment. It was recently demonstrated that the overexpression of the transmembrane tyrosine kinase receptor ErbB2 is able to increase the expression of FAS in a breast epithelial cell line, which in turn becomes susceptible to apoptosis by FAS inhibition. Considering that USP2a prevents the destruction of FAS through deubiquitination and that ErbB2 overexpression is associated with FAS production, the purpose of the present study was to investigate their mRNA levels by real time PCR in SCC samples and morphologically normal tissue after laser capture microdissection. We also evaluated ErbB2 and FAS protein levels by immunohistochemistry. Two distinct patterns of ErbB2 positivity were identified, a sharply demarcated membrane staining, found in the adjacent normal epithelium and well differentiated areas of the tumors, and a cytoplasmic reaction observed mainly in undifferentiated cells. Most of the lesions (97.06%) that showed a high expression of FAS were also positive for ErbB2 at the cell membrane (p=0.001) and both had correlated with the proliferation marker Ki-67. The immunolabeling for ErbB2 at the cell membrane was also stronger in histologically well differentiated lesions while cytoplasmic positivity was found in undifferentiated tumors. FAS and ErbB2 positivity were associated with microscopic characteristics as thickness and lymphatic embolization of the lesion. Our study also showed a strong positive correlation between ErbB2, FAS and USP2a mRNA expression in the SCC samples compared with normal morphologically tissue of the same source. Taken together, the results presented here show that FAS and ErbB2 are co-expressed in oral SCC and suggest that ErbB2 is able to regulate FAS production in these tumors. Moreover, our data point out that these proteins are significantly associated with a poor prognosis (AU) | |