Doctor of Philosophy, University Of Otago (2010)
Marlene Rabinovitch, Postdoctoral Faculty Sponsor
PAX genes have been shown to be critically required for the development of specific tissues and organs during embryogenesis. In addition, PAX genes are expressed in a handful of adult tissues where they are thought to play important roles, usually different from those in embryogenesis. A common theme in adult tissues is a requirement for PAX gene expression in adult stem cell maintenance or tissue regeneration. The connections between adult stem cell PAX gene expression and cancer are intriguing, and the literature is replete with examples of PAX gene expression in either situation. Here we systematically review the literature and present an overview of postnatal PAX gene expression in normal and cancerous tissue. We discuss the potential link between PAX gene expression in adult tissue and cancer. In addition, we discuss whether persistent PAX gene expression in cancer is favorable or unfavorable.
View details for DOI 10.3389/fgene.2012.00006
View details for PubMedID 22303411
The retinoblastoma protein (RB)-E2F1 pathway has a central role in regulating the cell cycle. Several PAX proteins (tissue-specific developmental regulators), including PAX8, interact with the RB protein, and thus regulate the cell cycle directly or indirectly. Here, we report that PAX8 expression is frequent in renal cell carcinoma, bladder, ovarian and thyroid cancer cell lines, and that silencing of PAX8 in cancer cell lines leads to a striking reduction in the expression of E2F1 and its target genes, as well as a proteasome-dependent destabilization of RB protein, with the RB1 mRNA level remaining unaffected. Cancer cells expressing PAX8 undergo a G(1)/S arrest and eventually senesce following PAX8 silencing. We demonstrate that PAX8 transcriptionally regulates the E2F1 promoter directly, and E2F1 transcription is enhanced after RB depletion. RB is recruited to the PAX8-binding site, and is involved in PAX8-mediated E2F1 transcription in cancer cells. Therefore, our results suggest that, in cancer, frequent and persistent expression of PAX8 is required for cell growth control through transcriptional activation of E2F1 expression and upregulation of the RB-E2F1 pathway.
View details for DOI 10.1038/onc.2011.190
View details for Web of Science ID 000298134700006
View details for PubMedID 21602887
PAX3 and MITF are important transcriptional activators in the melanocyte lineage and PAX3 is thought to control MITF expression during normal melanocyte differentiation. However, it is not clear whether this is still true in melanoma and whether the effects of knockdown of PAX3 on the inhibition of melanoma growth or survival are by its regulation of MITF. By western blot and quantitative real-time reverse transcription-PCR, we investigated the relationship between PAX3 and MITF expression in 27 metastatic melanoma and one immortalized melanocyte cell lines. All lines were found to express both PAX3 and MITF proteins but levels varied by 15 fold and more than 100 fold, respectively. The expression of PAX3 protein was correlated with that of MITF (r=0.75; P<0.001) but the expression of PAX3 protein and MITF mRNA was not. Immunofluorescence microscopy showed that individual cells expressed widely differing relative amounts of PAX3 and MITF protein. By MTT cell proliferation and flow cytometry assays, both MITF and PAX3 proteins seemed to be functional, as knockdown with siRNA led to reduced proliferation and induction of apoptosis. However, knockdown of PAX3 with small interfering RNA did not decrease MITF expression and vice versa. In one cell line (NZM15), silencing of PAX3 induced terminal differentiation whereas silencing of MITF induced expression of FOXD3, a repressor of melanogenesis. The results suggest that the melanoma lines used in this study show considerable phenotypic variation of expression of these two transcriptional activators and reflect a deregulation of the developmental process operating in the genesis of the melanocyte lineage, and that they probably function independently to enhance the survival of melanoma cells.
View details for PubMedID 21164369