Growth Arrest In Human Cells Research Articles

Abstract PL01-01: The role of telomeres and telomerase in aging and cancer

Abstract One of the fundamental differences in the behavior of human normal versus tumor cells is that most normal cells divide for a limited number of times (Hayflick Limit) whereas tumor cells can proliferate indefinitely (one of the hallmarks of cancer). It is widely believed that the biological function of cellular aging (senescence) is to serve as a mechanism for restricting cancer progression. It is now established that almost all advanced cancers express telomerase, and this provides the molecular mechanism for the bypass of both telomere-associated senescence. The following topics/questions will be discussed in this lecture. 1. Evidence that the telomere-based mechanism of cellular aging in human cells has held the test of time 2. The role of telomerase in bypassing telomere-based replicative senescence proves that the growth arrest of human cells with critically short telomeres is a key molecular basis of human cell aging 3. Progress in using telomerase inhibitors in targeting cancer 4. Development of accurate methods to quantitatively measure the shortest telomeres 5. Methods for safely using telomerase or telomerase activators for identifying and treating telomere diseases associated with aging? Goals and Objectives 1. To review the evidence that telomeres are a biomarker that is important in human aging and cancer. 2. To review the evidence that introduction of telomerase into normal cells does not lead to an increased risk of cancer and inhibition of telomerase can lead to cancer cell death 3. To review human diseases associated with telomere dysfunction and approaches to identifying and treating telomeropathies Citation Format: Jerry W. Shay. The role of telomeres and telomerase in aging and cancer. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr PL01-01.

DNA Damage and P53-Mediated Growth Arrest in Human Cells Treated with Platinum Nanoparticles

Platinum-based therapeutic agents are widely used in medicine. Thus, a thorough understanding of their mechanism of action in cells is warranted. This study investigates the uptake and bioactivity (e.g., cytotoxicity, genotoxicity and protein expression) of platinum nanoparticles (Pt-NPs, approximately 5-8 nm in size) in human cells. Pt-NPs capped with polyvinyl alcohol were synthesized, characterized and incubated with human cells. Uptake and the biological properties were evaluated through metabolic activity, genome integrity, cell cycle and protein expression. Pt-NPs entered the cells through diffusion, and localized inside the cytoplasm. Exposure to the Pt-NP increased DNA damage, accumulation of cells at the S-phase of the cell cycle and apoptosis. A significant number of cells recovered from the stress and formed colonies. Protein-expression levels uncovered upregulation of p53, phosphorylated p53, p21 and downregulation of proliferating cell nuclear antigen following Pt-NP treatment. Pro-caspase 3 and poly-ADP ribose polymerase and cyclin B levels were not altered in both the cell types after Pt-NP exposure. The results suggest p53 activation in Pt-NP-treated cells due to genotoxic stress, with subsequent activation of p21 leading to a proliferating cell nuclear antigen-mediated growth arrest and apoptosis. This study recommends development of Pt-NP-based anticancer agents by appropriate surface modifications to augment its innate anticancer activity.

Suppression of adenine nucleotide translocase-2 by vector-based siRNA in human breast cancer cells induces apoptosis and inhibits tumor growth in vitro and in vivo.

IntroductionAdenine nucleotide translocator (ANT) 2 is highly expressed in proliferative cells, and ANT2 induction in cancer cells is known to be directly associated with glycolytic metabolisms and carcinogenesis. In addition, ANT2 repression results in the growth arrest of human cells, implying that ANT2 is a candidate for cancer therapy based on molecular targeting.MethodsWe utilized an ANT2-specific RNA interference approach to inhibit ANT2 expression for evaluating its antitumor effect in vitro and in vivo. Specifically, to investigate the therapeutic potential of ANT2 repression, we used a DNA vector-based RNA interference approach by expressing shRNA to knockdown ANT2 in breast cancer cell lines overexpressing ANT2.ResultsANT2 shRNA treatment in breast cancer cell line MDA-MB-231 repressed cell growth as well as proliferation. In addition, cell cycle arrest, ATP depletion and apoptotic cell death characterized by the potential disruption of mitochondrial membrane were observed from the ANT2 shRNA-treated breast cancer cells. Apoptotic breast cancer cells transfected with ANT2 shRNA also induced a cytotoxic bystander effect that generates necrotic cell death to the neighboring cells. The intracellular levels of TNFα and TNF-receptor I were increased in ANT2 shRNA transfected cells and the bystander effect was partly blocked by anti-TNFα antibody. Ultimately, ANT2 shRNA effectively inhibited tumor growth in vivo.ConclusionThese results suggest that vector-based ANT2 RNA interference could be an efficient molecular therapeutic method for breast cancer with high expression of ANT2.

A Role for p53 in Maintaining and Establishing the Quiescence Growth Arrest in Human Cells

The p53 tumor suppressor protein induces transient growth arrest or apoptosis in response to genotoxic stress and mediates the irreversible growth arrest of cellular senescence. We present evidence here that p53 also contributes to the reversible, growth factor-dependent arrest of quiescence (G(0)). Microinjection of expression vectors encoding either MDM2 or a pRb-binding mutant of SV40 T antigen, both of which abrogate p53 function, stimulated quiescent normal human fibroblasts to initiate DNA synthesis and were 40-70% as effective as wild-type T antigen. Electrophoretic mobility shift and p53 transactivation assays showed that p53 activity was higher in quiescent and senescent cells compared with proliferating cells. As proliferating cells entered G(0) after growth factor withdrawal, the p53 mRNA level increased, followed by transient accumulation of the protein. Shortly thereafter, the expression (mRNA and protein) of p21, a p53 target gene and effector of cell cycle arrest, increased. Finally, stable expression of the HPV16 E6 oncogene or dominant negative p53 peptide, GSE-22, both of which inhibit p53 function, delayed entry into quiescence following growth factor withdrawal. Our data indicate that p53 is activated during both quiescence and senescence. They further suggest that p53 activity contributes, albeit not exclusively, to the quiescent growth arrest.