Tumor aggressiveness is independent of radiation quality in murine hepatocellular carcinoma and mammary tumor models.

PURPOSE: Estimating cancer risk associated with interplanetary space travel is complicated. Human exposure data to high atomic number, high-energy (HZE) radiation is lacking, so data from low linear energy transfer (low-LET) γ-ray radiation is used in risk models, with the assumption that HZE and γ-ray radiation have comparable biological effects. This assumption has been challenged by reports indicating that HZE radiation might produce more aggressive tumors. The goal of this research is to test whether high-LET HZE radiation induced tumors are more aggressive. MATERIALS AND METHODS: Murine models of mammary and liver cancer were used to compare the impact of exposure to 0.2Gy of 300MeV/n silicon ions, 3 Gy of γ-rays or no radiation. Numerous measures of tumor aggressiveness were assessed. RESULTS: For the mammary cancer models, there was no significant change in the tumor latency or metastasis in silicon-irradiated mice compared to controls. For the liver cancer models, we observed an increase in tumor incidence but not tumor aggressiveness in irradiated mice. CONCLUSION: Tumors in the HZE-irradiated mice were not more aggressive than those arising from exposure to low-LET γ-rays or spontaneously. Thus, enhanced aggressiveness does not appear to be a uniform characteristic of all tumors in HZE-irradiated animals.

Parthenolide Destabilizes Microtubules by Covalently Modifying Tubulin.

Detyrosination of the α-tubulin C-terminal tail is a post-translational modification (PTM) of microtubules that is key for many biological processes.1 Although detyrosination is the oldest known microtubule PTM,2-7 the carboxypeptidase responsible for this modification, VASH1/2-SVBP, was identified only 3 years ago,8,9 precluding genetic approaches to prevent detyrosination. Studies examining the cellular functions of detyrosination have therefore relied on a natural product, parthenolide, which is widely believed to block detyrosination of α-tubulin in cells, presumably by inhibiting the activity of the relevant carboxypeptidase(s).10 Parthenolide is a sesquiterpene lactone that forms covalent linkages predominantly with exposed thiol groups; e.g., on cysteine residues.11-13 Using mass spectrometry, we show that parthenolide forms adducts on both cysteine and histidine residues on tubulin itself, in vitro and in cells. Parthenolide causes tubulin protein aggregation and prevents the formation of microtubules. In contrast to epoY, an epoxide inhibitor of VASH1/2-SVBP,9 parthenolide does not block VASH1-SVBP activity in vitro. Lastly, we show that epoY is an efficacious inhibitor of microtubule detyrosination in cells, providing an alternative chemical means to block detyrosination. Collectively, our work supports the notion that parthenolide is a promiscuous inhibitor of many cellular processes and suggests that its ability to block detyrosination may be an indirect consequence of reducing the polymerization-competent pool of tubulin in cells.

Miro: A molecular switch at the center of mitochondrial regulation.

The orchestration of mitochondria within the cell represents a critical aspect of cell biology. At the center of this process is the outer mitochondrial membrane protein, Miro. Miro coordinates diverse cellular processes by regulating connections between organelles and the cytoskeleton that range from mediating contacts between the endoplasmic reticulum and mitochondria to the regulation of both actin and microtubule motor proteins. Recently, a number of cell biological, biochemical, and protein structure studies have helped to characterize the myriad roles played by Miro. In addition to answering questions regarding Miro's function, these studies have opened the door to new avenues in the study of Miro in the cell. This review will focus on summarizing recent findings for Miro's structure, function, and activity while highlighting key questions that remain unanswered.

Fisetin and 5-fluorouracil: Effective combination for PIK3CA-mutant colorectal cancer.

The normal colon epithelium is transformed into its neoplastic counterpart through a series of genetic alterations in driver genes including activating mutations in PIK3CA. Treatment often involves surgery followed by 5-fluorouracil (5-FU) based therapy, which has limited efficiency and serious side effects. We sought to determine whether fisetin, a dietary flavonoid, alone or in combination with 5-FU affected tumorigenesis in the mammalian intestine. We first determined the effect of fisetin, 5-FU or their combination on PIK3CA-mutant and PIK3CA wild-type colon cancer cells by assessing cell viability, colony formation, apoptosis and effects on PI3K/AKT/mTOR signaling. Treatment of PIK3CA-mutant cells with fisetin and 5-FU reduced the expression of PI3K, phosphorylation of AKT, mTOR, its target proteins, constituents of mTOR signaling complex and this treatment increased the phosphorylation of AMPKα. We then determined whether fisetin and 5-FU together or singly affected tumorigenesis in ApcMin/+ mice that also express constitutively active PI3K in the distal small intestine and colon. Tumor incidence was markedly lower in fisetin-treated FC1 3K1 ApcMin/+ mice that also express constitutively active PI3K in distal small intestine and colon, as compared to control animals, indicating that fisetin is a strong preventive agent. In addition, the combination of fisetin and 5-FU also reduced the total number of intestinal tumors. Fisetin could be used as a preventive agent plus an adjuvant with 5-FU for the treatment of PIK3CA-mutant colorectal cancer.