| Abstract
|
:
|
Pituitary tumor transforming gene (PTTG), also known as securing, is a novel oncogene that is expressed at high levels in most of the tumors analyzed to date. Overexpression of PTTG in mouse fibroblast (NIH 3T3) cells increases cell proliferation, induces cellular transformation and promotes tumor formation in nude mice. PTTG is a multi-domain and multifunction protein. Some functions of PTTG include inhibition of pre-mature sister chromatid separation, activation of transcription of c-myc oncogene, cell cycle regulation, and DNA repair. In some cancers such as thyroid, pituitary, esophageal, and colorectal tumors, high PTTG expression correlates with metastasis and poor prognosis. The PTTG gene encodes a protein of 203 amino acids and is consists of six exons and four introns. The PTTG promoter is specifically activated in tumors and is highly regulated by Spl and NF-Y nuclear factors. However, the precise mechanism by which PTTG mediates its tumorigenic function remains unclear. To this end, we determined the effect of PTTG on tumor metastasis and angiogenesis by determining its effect on secretion and expression of various angiogenic and metastatic factors including bFGF, VEGF, IL-8 and MMP-2. Using RT/PCR, ELISA and zymography we showed a significant increase in expression and secretion of bFGF, VEGF, IL-8 and MMP-2 in HEK293 cells on transfection of PTTG cDNA. Down regulation of PTTG expression by siRNA and a genetically deleted HCTI 1'6 (PTTG -/-) cell line showed significantly decrease in expression of MMP-2, which led to decreased invasion and migration of HCT116 (PTTG-/-) cells as compared to the HCT116 wild type. Taken together, our results confirm that PTTG is a potent tumorigenic gene that exerts its tumorigenic functions by increasing secretion and expression of VEGF, bFGF, IL-8 and MMP-2 and MTl-MMP. In addition expression of other angiogenic and adhesion molecules including beta-1, beta-3, alpha-5 and alpha-V integrins was also modulated by PTTG in HEK293 cells.
|