The mdm2 proto-oncogene sensitizes human medullary thyroid carcinoma cells to ionizing radiation

Ubiquitin-modifying enzymes in thyroid cancer：Mechanisms and functions

Thyroid cancer is the most common malignant tumor of the endocrine system, and evidence suggests that post-translational modifications (PTMs) and epigenetic alterations play an important role in its development. Recently, there has been increasing evidence linking dysregulation of ubiquitinating enzymes and deubiquitinases with thyroid cancer. This review aims to summarize our current understanding of the role of ubiquitination-modifying enzymes in thyroid cancer, including their regulation of oncogenic pathways and oncogenic proteins. The role of ubiquitination-modifying enzymes in thyroid cancer development and progression requires further study, which will provide new insights into thyroid cancer prevention, treatment and the development of novel agents.

The Use of Gene Therapy in Cancer Research and Treatment

Gene therapy involves identifying a gene of interest and then manipulating the expression of this gene through a variety of techniques. Here we specifically address gene therapy's role in cancer research. This paper will encompass thoroughly investigated techniques such as cancer vaccines and suicide gene therapy and the latest advancements in and applications of these techniques. It will also cover newer techniques such as Antisense Oligonucleotides and small interfering RNAs and how these technologies are being developed and used. The use of gene therapy continues to expand in cancer research and has an integral role in the advancement of cancer treatment.

PKCδ regulates Mdm2 independently of p53 in the apoptotic response to DNA damage

Apoptosis is the key process in which cells with defective genome can be eliminated. Dys-regulation of apoptosis causes accumulation of irreparable mutation arisen from DNA damage and is the underlying cause of carcinogenesis. PKCδ is a multifunctional kinase involved in signal transduction of genotoxic-induced apoptosis. Previous studies have demonstrated that PKCδ transactivates p53 in response to DNA damage. These findings led us to determine if Mdm2, a nuclear phospho-protein and negative regulator of p53, could also be a PKCδ-modulated substrate. We discovered that inhibition of PKCδ down-regulates Mdm2 protein expression regardless of p53 status. Given that Mdm2 mRNA change was detected in p53-proficient, but not deficient cells, PKCδ affected Mdm2 on the post-translational level. Interestingly, treatment of MG132 restored Mdm2 expression to the steady-state level. Further investigation showed that PKCδ inhibited Mdm2 ubiquitination in p53-deficient cells and loss of PKCδ resulted in an increase in Mdm2 proteosomal degradation. Moreover, P300/CBP-associated factor (PCAF), an ubiquitin ligase 3 for Mdm2, was observed to participate in Mdm2 ubiquitination by PKCδ inhibition and knock-down of PCAF rescued Mdm2 diminution. Finally, as shown for PKCδ, Mdm2 was also required to exert pro-apoptotic response caused by genotoxic agents in p53-null cells. In addition, overexpression of Mdm2 restored inhibitory effect of apoptosis in cells silenced for PKCδ. Taken together, we conclude that PKCδ regulates Mdm2 expression distinctively of p53 pathway by affecting Mdm2 ubiquitination and maintenance of Mdm2 expression by PKCδ is important to ensure normal genotoxic cell death response in human cancer cells.

Murine double minute 2: p53-independent roads lead to genome instability or death

The oncoprotein murine double minute 2 (Mdm2) is frequently overexpressed in many types of human malignancies. Although Mdm2 has an essential role in negatively regulating the p53 tumor suppressor, it also has less well characterized p53-independent functions that influence pathways that are crucial for controlling tumorigenesis. In addition to the impact Mdm2 has on p53-independent apoptosis, mounting evidence is linking increased Mdm2 levels to altered cell-cycle regulation, DNA replication and DNA repair leading to loss of genome stability. Mdm2 involvement in pathways that influence chromosome stability and cell death, distinct from its role in the p53 pathway, strengthens the position of Mdm2 as a desirable therapeutic target for the treatment of human cancers.

Murine double minute 2 as a therapeutic target for radiation sensitization of lung cancer

Murine double minute 2 (MDM2) inhibits p53-mediated functions, which are essential for therapies using DNA-damaging agents. The purpose of this study was to determine whether MDM2 inhibition enhances the radiosensitivity of a lung cancer model. The effects of MDM2 inhibition on tumor vasculature were also studied. Transient transfection of H460 lung cancer cells and human umbilical vascular endothelial cells (HUVEC) with antisense oligonucleotides (ASODN) against MDM2 resulted in a reduced level of MDM2 and increased levels of p21 and p53. Clonogenic assays showed that inhibition of MDM2 greatly decreased cell survival following irradiation. Quantification of apoptotic cells by 7-aminoactinomycin D staining and of senescent cells by X-gal staining showed that both processes were significantly increased in H460 cells treated with MDM2-specific ASODN and radiation. H460 xenografts that were treated with MDM2 ASODN plus radiotherapy also showed significant growth delay (P < 0.001) and increased apoptosis by terminal deoxynucleotidyl transferase-mediated nick end labeling staining. HUVECs transfected with MDM2-specific ASODN showed impaired viability and migration with decreased tube formation. Doppler studies showed that tumor blood flow was compromised when H460 xenografts were treated with MDM2-specific ASODN and radiation. A combination of radiotherapy and inhibition of MDM2 through the antisense approach results in improved tumor control in the H460 lung cancer model. This implies that a similar strategy should be investigated among patients with locally advanced lung cancer, receiving thoracic radiotherapy.

Retinoid-related molecule AGN193198 potently induces G2M arrest and apoptosis in bladder cancer cells

The novel synthetic retinoid-related molecule 4-[3-(1-heptyl-4,4-dimethyl-2-oxo-1,2,3,4-tetrahydroquinolin-6-yl)-3-oxo-propenyl]benzoic acid (AGN193198) neither binds effectively to retinoic acid receptors (RARs) and retinoid X receptors (RXRs) nor transactivates in RAR- and RXR-mediated reporter assays. Even so, AGN193198 is potent in inducing apoptosis in human prostate and breast carcinoma cells (Keedwell et al., Cancer Res 2004;64:3302-12). Here, we extend these findings to show that AGN193198 potently and rapidly induces apoptosis in bladder carcinoma cell lines. One micromolar of AGN193198 completely abolished the growth of the transitional cell carcinoma lines UM-UC-3 and J82, and the squamous cell carcinoma line SCaBER; the transitional cell papilloma line RT-4 was slightly less sensitive to the growth inhibitory effect of AGN193198. Treated cells accumulated in the G2M phase of the cell cycle. This was accompanied by apoptosis, as revealed by staining cells for exposure of phosphatidylserine at their surface (binding of Annexin V) and FACS analysis of propidium iodide labeled cells. As reported for prostate cancer cells, AGN193198 provoked rapid activation of caspases-3 (by 6 hr), -8 (by 16 hr) and -9 (by 6 hr) in bladder cancer cells. These findings suggest that AGN193198 and related compounds, whose mechanism of action does not appear to involve RARs and RXRs, may be useful in the treatment of bladder cancer.

Irod/Ian5: an inhibitor of gamma-radiation- and okadaic acid-induced apoptosis

Protein phosphatase-directed toxins such as okadaic acid (OA) are general apoptosis inducers. We show that a protein (inhibitor of radiation- and OA-induced apoptosis, Irod/Ian5), belonging to the family of immune-associated nucleotide binding proteins, protected Jurkat T-cells against OA- and gamma-radiation-induced apoptosis. Unlike previously described antiapoptotic proteins Irod/Ian5 did not protect against anti-Fas, tumor necrosis factor-alpha, staurosporine, UV-light, or a number of chemotherapeutic drugs. Irod antagonized a calmodulin-dependent protein kinase II-dependent step upstream of activation of caspase 3. Irod has predicted GTP-binding, coiled-coil, and membrane binding domains. Irod localized to the centrosomal/Golgi/endoplasmic reticulum compartment. Deletion of either the C-terminal membrane binding domain or the N-terminal GTP-binding domain did not affect the antiapoptotic function of Irod, nor the centrosomal localization. The middle part of Irod, containing the coiled-coil domain, was therefore responsible for centrosomal anchoring and resistance toward death. Being widely expressed and able to protect also nonimmune cells, the function of Irod may not be limited to the immune system. The function and localization of Irod indicate that the centrosome and calmodulin-dependent protein kinase II may have important roles in apoptosis signaling.