Biomedical subjects

Tariq Hamid

Publications and source records attributed to Tariq Hamid.

3 recordsLinked to original sources

PubMed2005

Ectopic expression of PTTG1/securin promotes tumorigenesis in human embryonic kidney cells.

BACKGROUND: Pituitary tumor transforming gene1 (PTTG1) is a novel oncogene that is expressed in most tumors. It encodes a protein that is primarily involved in the regulation of sister chromatid separation during cell division. The oncogenic potential of PTTG1 has been well characterized in the mouse, particularly mouse fibroblast (NIH3T3) cells, in which it induces cell proliferation, promotes tumor formation and angiogenesis. Human tumorigenesis is a complex and a multistep process often requiring concordant expression of a number of genes. Also due to differences between rodent and human cell biology it is difficult to extrapolate results from mouse models to humans. To determine if PTTG1 functions similarly as an oncogene in humans, we have characterized its effects on human embryonic kidney (HEK293) cells. RESULTS: We report that introduction of human PTTG1 into HEK293 cells through transfection with PTTG1 cDNA resulted in increased cell proliferation, anchorage-independent growth in soft agar, and formation of tumors after subcutaneous injection of nu/nu mice. Pathologic analysis revealed that these tumors were poorly differentiated. Both analysis of HEK293 cells transiently transfected with PTTG1 cDNA and analysis of tumors developed on injection of HEK293 cells that had been stably transfected with PTTG1 cDNA indicated significantly higher levels of secretion and expression of bFGF, VEGF and IL-8 compared to HEK293 cells transfected with pcDNA3.1 vector or uninvolved tissues collected from the mice. Mutation of the proline-rich motifs at the C-terminal of PTTG1 abolished its oncogenic properties. Mice injected with this mutated PTTG1 either did not form tumors or formed very small tumors. Taken together our results suggest that PTTG1 is a human oncogene that possesses the ability to promote tumorigenesis in human cells at least in part through the regulation of expression or secretion of bFGF, VEGF and IL-8. CONCLUSIONS: Our results demonstrate that PTTG1 is a potent human oncogene and has the ability to induce cellular transformation of human cells. Overexpression of PTTG1 in HEK293 cells leads to an increase in the secretion and expression of bFGF, VEGF and IL-8. Mutation of C-terminal proline-rich motifs abrogates the oncogenic function of PTTG1. To our knowledge, this is the first study demonstrating the importance of PTTG1 in human tumorigenesis.

Animals↗

PubMed2004

PTTG/securin activates expression of p53 and modulates its function.

BACKGROUND: Pituitary tumor transforming gene (PTTG) is a novel oncogene that is expressed abundantly in most tumors. Overexpression of PTTG induces cellular transformation and promotes tumor formation in nude mice. PTTG has been implicated in various cellular processes including sister chromatid separation during cell division as well as induction of apoptosis through p53-dependent and p53-independent mechanisms. The relationship between PTTG and p53 remains unclear, however. RESULTS: Here we report the effects of overexpression of PTTG on the expression and function of p53. Our results indicate that overexpression of PTTG regulates the expression of the p53 gene at both the transcriptional and translational levels and that this ability of PTTG to activate the expression of p53 gene is dependent upon the p53 status of the cell. Deletion analysis of the p53 gene promoter revealed that only a small region of the p53 gene promoter is required for its activation by PTTG and further indicated that the activation of p53 gene by PTTG is an indirect effect that is mediated through the regulation of the expression of c-myc, which then interacts with the p53 gene promoter. Our results also indicate that overexpression of PTTG stimulates expression of the Bax gene, one of the known downstream targets of p53, and induces apoptosis in a human embryonic kidney cell line (HEK293). This stimulation of bax expression by PTTG is indirect and is mediated through modulation of p53 gene expression. CONCLUSIONS: Overexpression of PTTG activates the expression of p53 and modulates its function, with this action of PTTG being mediated through the regulation of c-myc expression. PTTG also up-regulates the activity of the bax promoter and increases the expression of bax through modulation of p53 expression.

Apoptosis↗

PubMed2003

Characterization of the role of Sp1 and NF-Y in differential regulation of PTTG/securin expression in tumor cells.

Pituitary tumor transforming gene (PTTG), also known as securin, is a regulator of cell division that is overexpressed in many tumors. Its expression is cell cycle regulated, although its transcriptional regulation is yet to be determined. The 5' RACE analysis of the human testis mRNA revealed the existence of a previously unreported transcription start site at 317 bp upstream of the translation start site (ATG). This gene is known to be composed of five exons and four introns, which is now changed to six exons and five introns. To map the promoter region, and to understand its regulation, we designed several fusion constructs of the 5' flanking region of PTTG including the sequence from nucleotide -1373 to -3 (relative to the translation start site) to a luciferase reporter gene. Transient transfection of these constructs in prostate cancer cell line (PC-3) and fibroblast cell line (HS27) confirmed the existence of promoter for PTTG between nucleotides -161 and -3 (in relation to translation start site). The 5' and 3' deletion analysis of the PTTG flanking region and electrophoretic mobility shift assays revealed binding of Sp1 and NF-Y transcription factors within nucleotides -540 to -500. Chromatin immunoprecipitation (ChIP) assays of the HS27 and PC-3 cells revealed the binding of Sp1 protein to PTTG promoter sequence in vivo. Site-directed mutagenesis of the Sp1 consensus sequence resulted in approximately 70% reduction of the overall transcriptional activation of the PTTG promoter, whereas mutation of the NF-Y sequence resulted in approximately 25% reduction. Deletion of both Sp1 and NF-Y consensus sequences resulted in 90% loss of PTTG promoter activity. It was further observed, by Western blot analysis, that the levels of Sp1 protein are higher in PC-3 cells when compared to levels in HS27 cells, possibly contributing to a tissue-specific effect. Our studies indicate an important role of Sp1 in transcription regulation of PTTG expression in tumors.

Binding Sites↗