Abstract
BackgroundPituitary tumor transforming gene (PTTG) is a novel oncogene that is expressed at higher level in most of the tumors analyzed to date compared to normal tissues. Existence of a relationship between PTTG levels and tumor angiogenesis and metastasis has been reported. However, the mechanisms by which PTTG achieve these functions remain unknown. In the present study, we investigated the effect of overexpression of PTTG on secretion and expression of metastasis-related metalloproteinase-2 (MMP-2) in HEK293 cells, cell migration, invasion and tubule formation.ResultsTransient or stable transfection of HEK293 cells with PTTG cDNA showed a significant increase in secretion and expression of MMP-2 measured by zymography, reverse transcriptase (RT/PCR), ELISA, and MMP-2 gene promoter activity. Furthermore, in our studies, we showed that tumor developed in nude mice on injection of HEK293 cells that constitutively express PTTG expressed high levels of both MMP-2 mRNA and protein, and MMP-2 activity. Conditioned medium collected from the HEK293 cells overexpressing PTTG showed a significant increase in cell migration, invasion and tubule formation of human umbilical vein endothelial cells (HUVEC). Pretreatment of conditioned medium with MMP-2-specific antibody significantly decreased these effects, suggesting that PTTG may contribute to tumor angiogenesis and metastasis via activation of proteolysis and increase in invasion through modulation of MMP-2 activity and expression.ConclusionOur results provide novel information that PTTG contributes to cell migration, invasion and angiogenesis by induction of MMP-2 secretion and expression. Furthermore, we showed that tumors developed in nude mice on injection of HEK293 cells that constitutively express PTTG induce expression of MMP-2 and significantly increase its functional activity, suggesting a relationship between PTTG levels and MMP-2 which may play a critical role in regulation of tumor growth, angiogenesis and metastasis. Blocking of function of PTTG or down regulation of its expression in tumors may result in suppression of tumor growth and metastasis, through the down regulation of MMP-2 expression and activity. To our knowledge, this study is the first study demonstrating the modulation of MMP-2 expression and biological activity by PTTG.
Highlights
Pituitary tumor transforming gene (PTTG) is a novel oncogene that is expressed at higher level in most of the tumors analyzed to date compared to normal tissues
And 2C, transfection of HEK293 cells with PTTG cDNA resulted in enhanced secretion of metastasis-related metalloproteinase-2 (MMP-2) (~2-3fold) but not MMP-9 secretion. These results were further confirmed by ELISA, which showed ~5-fold increase in MMP-2 levels in conditioned medium (CM) collected from HEK293 cells compared to CM collected from cells transfected with pcDNA3.1 vector (Fig. 2C)
We clearly showed that overexpression of PTTG in HEK293 cells resulted in a significant increase in secretion of MMP-2 (Fig. 2) in the medium and its mRNA levels in cells expressing PTTG compared to cells transfected with pcDNA3.1 vector (Fig. 3)
Summary
Pituitary tumor transforming gene (PTTG) is a novel oncogene that is expressed at higher level in most of the tumors analyzed to date compared to normal tissues. From a patient survival perspective point of view, understanding the mechanisms of angiogenesis and metastasis for the development of new therapeutics is a critical step to treat tumors [2,3]. In this contest, many oncogenes have been reported to play important roles in tumor angiogenesis and metastasis. A novel oncogene, pituitary tumor transforming gene (PTTG), known as securin, has been reported to play a vital role in tumor angiogenesis [4]. The degradation of PTTG most likely occurs via ubiquitination since PTTG contains a D box which is required for such proteolysis [9]
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