Wip1 abrogation decreases intestinal tumor frequency in APC(Min/+) mice irrespective of radiation quality

High-LET-Radiation-Induced Persistent DNA Damage Response Signaling and Gastrointestinal Cancer Development

Ionizing radiation (IR) dose, dose rate, and linear energy transfer (LET) determine cellular DNA damage quality and quantity. High-LET heavy ions are prevalent in the deep space environment and can deposit a much greater fraction of total energy in a shorter distance within a cell, causing extensive DNA damage relative to the same dose of low-LET photon radiation. Based on the DNA damage tolerance of a cell, cellular responses are initiated for recovery, cell death, senescence, or proliferation, which are determined through a concerted action of signaling networks classified as DNA damage response (DDR) signaling. The IR-induced DDR initiates cell cycle arrest to repair damaged DNA. When DNA damage is beyond the cellular repair capacity, the DDR for cell death is initiated. An alternative DDR-associated anti-proliferative pathway is the onset of cellular senescence with persistent cell cycle arrest, which is primarily a defense mechanism against oncogenesis. Ongoing DNA damage accumulation below the cell death threshold but above the senescence threshold, along with persistent SASP signaling after chronic exposure to space radiation, pose an increased risk of tumorigenesis in the proliferative gastrointestinal (GI) epithelium, where a subset of IR-induced senescent cells can acquire a senescence-associated secretory phenotype (SASP) and potentially drive oncogenic signaling in nearby bystander cells. Moreover, DDR alterations could result in both somatic gene mutations as well as activation of the pro-inflammatory, pro-oncogenic SASP signaling known to accelerate adenoma-to-carcinoma progression during radiation-induced GI cancer development. In this review, we describe the complex interplay between persistent DNA damage, DDR, cellular senescence, and SASP-associated pro-inflammatory oncogenic signaling in the context of GI carcinogenesis.

Countermeasure development against space radiation-induced gastrointestinal carcinogenesis: Current and future perspectives

A significantly higher probability of space radiation-induced gastrointestinal (GI) cancer incidence and mortality after a Mars mission has been projected using biophysical and statistical modeling approaches, and may exceed the current NASA mandated limit of less than 3% REID (risk of exposure-induced death). Since spacecraft shielding is not fully effective against heavy-ion space radiation, there is an unmet need to develop an effective medical countermeasure (MCM) strategy against heavy-ion space radiation-induced GI carcinogenesis to safeguard astronauts. In the past, we have successfully applied a GI cancer mouse model approach to understand space radiation-induced GI cancer risk and associated molecular signaling events. We have also tested several potential MCMs to safeguard astronauts during and after a prolonged space mission. In this review, we provide an updated summary of MCM testing using the GI cancer mouse model approach, lessons learned, and a perspective on the senescence signaling targeting approach for desirable protection against space radiation-induced GI carcinogenesis. Furthermore, we also discuss some of the advanced senotherapeutic candidates/combinations as a potential MCM for space radiation-induced GI carcinogenesis.

Phosphatase magnesium-dependent 1 δ (PPM1D), serine/threonine protein phosphatase and novel pharmacological target in cancer

Aberrations in DNA damage response genes are recognized mediators of tumorigenesis and resistance to chemo- and radiotherapy. While protein phosphatase magnesium-dependent 1 δ (PPM1D), located on the long arm of chromosome 17 at 17q22-23, is a key regulator of cellular responses to DNA damage, amplification, overexpression, or mutation of this gene is important in a wide range of pathologic processes. In this review, we describe the physiologic function of PPM1D, as well as its role in diverse processes, including fertility, development, stemness, immunity, tumorigenesis, and treatment responsiveness. We highlight both the advances and limitations of current approaches to targeting malignant processes mediated by pathogenic alterations in PPM1D with the goal of providing rationale for continued research and development of clinically viable treatment approaches for PPM1D-associated diseases.

Intestinal stem cells acquire premature senescence and senescence associated secretory phenotype concurrent with persistent DNA damage after heavy ion radiation in mice

Heavy ion radiation, prevalent in outer space and relevant for radiotherapy, is densely ionizing and poses risk to stem cells that are key to intestinal homeostasis. Currently, the molecular spectrum of heavy ion radiation-induced perturbations in intestinal stem cells (ISCs), that could trigger intestinal pathologies, remains largely unexplored. The Lgr5-EGFP-IRES-creERT mice were exposed to 50 cGy of iron radiation. Mice were euthanized 60 d after exposure and ISCs were sorted using fluorescence activated cell sorting. Reactive oxygen species (ROS) and mitochondrial superoxide were measured using fluorescent probes. Since DNA damage is linked to senescence and senescent cells acquire senescence-associated secretory phenotype (SASP), we stained ISCs for both senescence markers p16, p21, and p19 as well as SASP markers IL6, IL8, and VEGF. Due to potential positive effects of SASP on proliferation, we also stained for PCNA. Data show increased ROS and ongoing DNA damage, by staining for γH2AX, and 53BP1, along with accumulation of senescence markers. Results also showed increased SASP markers in senescent cells. Collectively, our data suggest that heavy-ion-induced chronic stress and ongoing DNA damage is promoting SASP in a fraction of the ISCs, which has implications for gastrointestinal function, inflammation, and carcinogenesis in astronauts and patients.

The role of PPM1D in cancer and advances in studies of its inhibitors

A greater understanding of factors causing cancer initiation, progression and evolution is of paramount importance. Among them, the serine/threonine phosphatase PPM1D, also referred to as wild-type p53-induced phosphatase 1 (Wip1) or protein phosphatase 2C delta (PP2Cδ), is emerging as an important oncoprotein due to its negative regulation on a number of crucial cancer suppressor pathways. Initially identified as a p53-regulated gene, PPM1D has been afterwards found amplified and more recently mutated in many human cancers such as breast cancer. The latest progress in this field further reveals that selective inhibition of PPM1D to delay tumor onset or reduce tumor burden represents a promising anti-cancer strategy. Here, we review the advances in the studies of the PPM1D activity and its relevance to various cancers, and recent progress in development of PPM1D inhibitors and discuss their potential application in cancer therapy. Consecutive research on PPM1D and its relationship with cancer is essential, as it ultimately contributes to the etiology and treatment of cancer.

Genomic Instability and Carcinogenesis of Heavy Charged Particles Radiation: Clinical and Environmental Implications

One of the uses of ionizing radiation is in cancer treatment. The use of heavy charged particles for treatment has been introduced in recent decades because of their priority for deposition of radiation energy in the tumor, via the Bragg peak phenomenon. In addition to medical implications, exposure to heavy charged particles is a crucial issue for environmental and space radiobiology. Ionizing radiation is one of the most powerful clastogenic and carcinogenic agents. Studies have shown that although both low and high linear energy transfer (LET) radiations are carcinogenic, their risks are different. Molecular studies have also shown that although heavy charged particles mainly induce DNA damage directly, they may be more potent inducer of endogenous generation of free radicals compared to the low LET gamma or X-rays. It seems that the severity of genotoxicity for non-irradiated bystander cells is potentiated as the quality of radiation increases. However, this is not true in all situations. Evidence suggests the involvement of some mechanisms such as upregulation of pro-oxidant enzymes and change in the methylation of DNA in the development of genomic instability and carcinogenesis. This review aimed to report important issues for genotoxicity of carcinogenic effects of heavy charged particles. Furthermore, we tried to explain some mechanisms that may be involved in cancer development following exposure to heavy charged particles.

The application of ApcMin/+ mouse model in colorectal tumor researches

PURPOSE

Apc^Min/+ mouse is an excellent animal model bearing multiple intestinal neoplasia, used to simulate human familial adenomatous polyposis and colorectal tumors. The key point of this model is the mutation of Apc gene, which is a significant tumor-suppressor gene in the Wnt signaling pathway. There are also some other possible mechanisms responsible for the development of colorectal tumors in the Apc^Min/+ mouse model, such as tumor-associated signaling pathways activation, the changes of tumor-related genes, and the involvement of some related proteins or molecules.

METHODS

The relevant literatures about Apc^Min/+ mouse model from PUBMED databases are reviewed in this study.

RESULTS

In recent years, increasing studies have focused on the application of Apc^Min/+ mouse model in colorectal tumor, trying to find effective therapeutic targets for further use.

CONCLUSION

This article will give a brief review on the related molecular mechanisms of the Apc^Min/+ mouse model and its application in colorectal tumor researches.

Space radiation exposure persistently increased leptin and IGF1 in serum and activated leptin-IGF1 signaling axis in mouse intestine

Travel into outer space is fraught with risk of exposure to energetic heavy ion radiation such as ⁵⁶Fe ions, which due to its high linear energy transfer (high-LET) characteristics deposits higher energy per unit volume of tissue traversed and thus more damaging to cells relative to low-LET radiation such as γ rays. However, estimates of human health risk from energetic heavy ion exposure are hampered due to lack of tissue specific in vivo molecular data. We investigated long-term effects of ⁵⁶Fe radiation on adipokines and insulin-like growth factor 1 (IGF1) signaling axis in mouse intestine and colon. Six- to eight-week-old C57BL/6J mice were exposed to 1.6 Gy of ⁵⁶Fe ions. Serum and tissues were collected up to twelve months post-irradiation. Serum was analyzed for leptin, adiponectin, IGF1, and IGF binding protein 3. Receptor expressions and downstream signaling pathway alterations were studied in tissues. Irradiation increased leptin and IGF1 levels in serum, and IGF1R and leptin receptor expression in tissues. When considered along with upregulated Jak2/Stat3 pathways and cell proliferation, our data supports the notion that space radiation exposure is a risk to endocrine alterations with implications for chronic pathophysiologic changes in gastrointestinal tract.

Control of stress signaling in stem cells: crossroads of stem cells and cancer

Tumorigenesis is a relatively rare event in the human body considering the enormous number of cells composing our body and the frequent occurrence of genetic mutations in each cell. Nevertheless, the cells that happen to meet the minimum requirements can be transformed when stressed by a variety of oncogenic stimulations, then progress to form tumors. The vigorous competition between oncogenic signaling and tumor-suppressor defense is a critical determinant of cellular fate, which can be either tumorigenic transformation or cellular senescence/apoptosis depending on "who wins the battle." Recently, a number of cancers have been reported to originate from stem cells, whose self-renewing properties are normally reduced by innate tumor suppressors. Therefore, exploring the innate mechanism by which stem cells modulate tumor suppressors to maintain their "stemness" may provide valuable clues to characterize the distinctive oncogenic susceptibility of stem cells. This review is focused on the recent advances in the field of tumorigenesis of stem cells and on the associated molecular mechanisms.

Colorectal Carcinogenesis, Radiation Quality, and the Ubiquitin-Proteasome Pathway

Adult colorectal epithelium undergoes continuous renewal and maintains homeostatic balance through regulated cellular proliferation, differentiation, and migration. The canonical Wnt signaling pathway involving the transcriptional co-activator β-catenin is important for colorectal development and normal epithelial maintenance, and deregulated Wnt/β-catenin signaling has been implicated in colorectal carcinogenesis. Colorectal carcinogenesis has been linked to radiation exposure, and radiation has been demonstrated to alter Wnt/β-catenin signaling, as well as the proteasomal pathway involved in the degradation of the signaling components and thus regulation of β-catenin. The current review discusses recent progresses in our understanding of colorectal carcinogenesis in relation to different types of radiation and roles that radiation quality plays in deregulating β-catenin and ubiquitin-proteasome pathway (UPP) for colorectal cancer initiation and progression.