Post-initiation chemopreventive effects of dietary bovine lactoferrin on 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-induced lung tumorigenesis in female A/J mice

We investigated the effects of bovine LF (bLF) on different phases of NNK-induced lung tumorigenesis in A/J mice. Mice were orally administered 0.02, 0.2 and 2% bLF during the initiation phase, and 2% bLF during the whole tumorigenesis phase or post-initiation phase. Administered bLF during the post-initiation phase showed significant reduction of macroscopical lung nodules, and immunohistochemically decreased expression levels of cell proliferation marker and increased expression levels of apoptosis marker in lung proliferative lesions. bLF might inhibit NNK-induced mouse lung tumorigenesis, only when given limited to the post-initiation phase, through modification of cell proliferation and/or apoptosis.     

Intrinsic resistance to apoptosis of colon epithelial cells is a potential determining factor in the susceptibility of the A/J mouse strain to dimethylhydrazine-induced colon tumorigenesis

Alterations in the delicate balance between cell proliferation and cell death disrupt colon homeostasis and serve as determining factors in colon tumorigenesis. The two mouse strains, AKR/J (resistant) and A/J (susceptible), have been widely used as models for dimethylhydrazine-induced colon tumorigenesis. This study examined whether the differential susceptibilities of the two mouse strains to the tumorigenic effect of dimethylhydrazine were associated with intrinsic differences in the apoptotic machinery of the colon epithelial cells. While acute exposure to dimethylhydrazine caused massive apoptosis of colon epithelial cells in AKR/J mice, the effect was considerably less in A/J mice. Apoptosis in AKR/J mice occurred not only in the luminal side of the mucosa but also deep in the colonic crypts. In addition, this apoptosis appeared to involve caspase-3. The increased sensitivity of AKR/J to dimethylhydrazine was associated with a persistent expression of tumor necrosis factor (TNF) but not of its receptors. After establishing a new method for isolating primary colon epithelial cells, we determined that cells derived from A/J mice were substantially more resistant to apoptosis in response to dimethylhydrazine or to a combination of TNF, cyclohexamide, and butyrate compared to cells from AKR/J mice. These results strongly suggest that a higher intrinsic resistance to apoptosis of colon epithelial cells may be an important determinant of predisposition to colon tumorigenesis in the A/J mouse strain.     

Curcumin modifies Apc(min) apoptosis resistance and inhibits 2-amino 1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) induced tumour formation in Apc(min) mice

Curcumin, the active ingredient of the rhizome of Curcuma longa, promotes apoptosis and may have chemopreventive properties. This study investigates the effects of curcumin on apoptosis and tumorigenesis in male Apc(min) mice treated with the human dietary carcinogen, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). Intestinal epithelial apoptotic index in response to PhIP treatment was approximately twice as great in the wild-type C57BL/6 APC(+/+) strain than in Apc(min) mice (3.7% Apc(+/+) versus 1.9% Apc(min); P < 0.001). PhIP promoted tumour formation in Apc(min) proximal small intestine (4.6 tumours per mouse, PhIP treated versus 2.1 tumours per mouse, control untreated; P < 0.05). Curcumin enhanced PhIP-induced apoptosis (4.0% curcumin + PhIP versus 2.1% PhIP alone; P < 0.01) and inhibited PhIP-induced tumorigenesis in the proximal small intestine of Apc(min) mice (2.2 tumours per mouse, curcumin + PhIP versus 4.6 tumours per mouse PhIP alone; P < 0.05). This study shows that the Apc(min) genotype is associated with resistance to PhIP-induced apoptosis in intestinal epithelium. Curcumin attenuates Apc(min) resistance to PhIP-induced apoptosis and inhibits PhIP-induced tumorigenesis in proximal Apc(min) mouse small intestine.     

Identification of spontaneous programmed cell death during development of human breast cancer

Breast tumorigenesis proceeds through an accumulation of specific genetic alteration. Breast malignant transformation is dependent not only on the rate of cell production but also on apoptosis, a genetically programmed process of autonomous cell death. We investigated whether breast tumorigenesis involves an altered susceptibility to apoptosis by examining normal breast epithelium and breast cancer samples. We found there is a significant inhibition of spontaneous apoptosis in breast cancer cells compared with normal breast epithelium. The inhibition of apoptosis in breast cancer may contribute to neoplastic transformation.     

Role of polyamines in arginine-dependent colon carcinogenesis in Apc(Min) (/+) mice

We evaluated the role of polyamines in arginine-dependent intestinal tumorigenesis in Apc(Min) (/+) mice. Arginine is a substrate for ornithine synthesis and thus can influence polyamine production. Supplementing the diet with arginine increased intestinal and colonic polyamine levels and colonic carcinogenesis. Inhibiting polyamine synthesis with D,L-alpha-diflouromethylornithine (DFMO) decreased small intestinal and colonic polyamine pools. In mice provided basal diet, but not when supplemented with arginine, DFMO decreased small intestinal tumor number and burden, and increased intestinal apoptosis. In mice provided supplemental arginine in the diet, DFMO induced late apoptosis and decreased tumorigenesis in the colon. DFMO slightly reduced tumor incidence, number, and size while significantly decreasing tumor burden and grade. These changes in colon tumorigenesis did not occur in mice not provided supplemental arginine. Our study indicates that polyamines play unique roles in intestinal and colonic carcinogenesis in Apc(Min) (/+) mice. Inhibition of polyamine synthesis suppresses the arginine-dependent risk of colon tumorigenesis, resulting in apoptosis induction and decreased tumorigenesis, in this murine model.     

Bax regulates c-Myc-induced mammary tumour apoptosis but not proliferation in MMTV-c-myc transgenic mice

The expression of the proto-oncogene c-myc is frequently deregulated, via multiple mechanisms, in human breast cancers. Deregulated expression of c-myc contributes to mammary epithelial cell transformation and is causally involved in mammary tumorigenesis in MMTV-c-myc transgenic mice. c-Myc is known to promote cellular proliferation, apoptosis, genomic instability and tumorigenesis in several distinct tissues, both in vivo and in vitro. Expression of the proapoptotic regulatory gene bax is reduced or absent in human breast cancers, and c-Myc has been shown to regulate the expression of Bax, as well as cooperate with Bax in controlling apoptosis in a fibroblast model. Additionally, loss of bax reduces c-Myc-induced apoptosis in lymphoid cells and increases c-Myc-mediated lymphomagenesis in vivo. In order to assess whether loss of bax could influence c-Myc-induced apoptosis and tumorigenesis in the mammary gland in vivo, we generated MMTV-c-myc transgenic mice in which neither, one, or both wild-type alleles of bax were eliminated. Haploid loss of bax in MMTV-c-myc transgenic mice resulted in significantly reduced mammary tumour apoptosis. As anticipated for an apoptosis-regulatory gene, loss of the wild-type bax alleles did not significantly alter cellular proliferation in either mammary adenocarcinomas or dysplastic mammary tissues. However, in contrast to c-Myc-mediated lymphomagenesis, loss of one or both alleles of bax in MMTV-c-myc transgenic mice did not significantly enhance mammary tumorigenesis, despite evidence that haploid loss of bax might modestly increase mammary tumour multiplicity. Our results demonstrate that Bax contributes significantly to c-Myc-induced apoptosis in mammary tumours. In addition, they suggest that in contrast to c-Myc-induced lymphomagenesis, mammary tumorigenesis induced by deregulated c-myc expression requires some amount of Bax expression.     

Role of MAP kinase in tumor progression and invasion

Activation of the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway is a frequent event in tumorigenesis. MAPKs have been implicated in cell migration, proteinase-induction, regulation of apoptosis, and angiogenesis, events that are essential for successful completion of metastasis. In this review, we discuss the potential role that MAPKs play in metastasis by regulating cell migration, proteinase-induction and apoptosis.     

Wnt/β-catenin信号转导途径异常在脑胶质瘤发生中的作用

Wnt/β-catenin信号转导途径与脑胶质瘤的发生发展密切相关.Wnt/β-catenin信号转导途径抑制因子及部分成员的异常表达能够促进胶质瘤细胞增殖,并抑制凋亡,从而导致胶质瘤的发生.研究Wnt/β-catenin信号转导途径与胶质瘤发生发展的关系可增进对胶质瘤发病机制的认识,并有望成为胶质瘤基因治疗的新靶点.     

Radiation-induced tumorigenesis in preneoplastic mouse mammary glands in vivo: Significance of p53 status and apoptosis

In mouse mammary tumorigenesis, p53 mutations facilitate tumorigenesis in concert with other oncogenic alterations. Ionizing radiation enhances tumorigenesis in preneoplastic mammary outgrowth lines and induces p53-dependent apoptosis. We asked if normal p53 function modulates radiation-induced tumorigenesis in preneoplastic mammary lesions by affecting the apoptotic pathway of cell deletion. Three different hyperplastic outgrowth lines were compared. Outgrowth line D1 overexpressed wild-type p53 and responded to irradiation with enhanced tumorigenicity but no induction of apoptosis. Outgrowth line TM12 exhibited normal wild-type p53 expression and responded to irradiation with no alteration in tumorigenicity but with a marked increase in apoptosis. Outgrowth line TM2L also exhibited normal wild-type p53 expression and responded to irradiation with a marked enhancement in both tumorigenicity and apoptosis. These results indicate that the two radiation-induced responses, apoptosis and tumorigenesis, are dissociable events in the mammary gland. Furthermore, radiation-induced tumorigenicity was not abrogated by either enhanced wild-type p53 expression or a robust apoptotic response. The radiation dose of 5 Gy most likely induces multiple genetic alterations in surviving cells, including genomic instability, and this may account for the tumorigenicity. Future experiments will examine lower doses of irradiation that still induce a significant apoptotic response but significantly less genomic instability. Mol. Carcinog. 22:199–207, 1998. © 1998 Wiley-Liss, Inc.     

Calpain 6 supports tumorigenesis by inhibiting apoptosis and facilitating angiogenesis

Since calpain 6 is overexpressed in uterine cervical cancer tissue compared to normal tissue, we sought to define the role of calpain 6 during tumorigenesis. We overexpressed calpain 6 or inhibited calpain 6 in human cervical cancer cells (HeLa cells) and human umbilical vein endothelial cells (HUVECs), and measured cisplatin-mediated apoptosis and VEGF-mediated angiogenesis. The results indicated that calpain 6 supported tumorigenesis by inhibiting apoptosis and facilitating angiogenesis. To our knowledge, this result is the first evidence implicating calpain 6 in tumorigenesis, and it reveals calpain 6 as a novel therapeutic target for certain types of cancers.     

Orphan receptor TR3 participates in cisplatin-induced apoptosis via Chk2 phosphorylation to repress intestinal tumorigenesis

Cisplatin is a widely used antitumor agent that induces aggressive cancer cell death via triggering cellular proteins involved in apoptosis. Here, we demonstrate that cisplatin effectively induces orphan nuclear receptor TR3 phosphorylation by activating Chk2 kinase activity and promoting cross talk between these two proteins, thereby contributing to the repression of intestinal tumorigenesis via apoptosis. Mechanistic analysis has demonstrated that Chk2-induced phosphorylation enables TR3 to bind to its response elements on the promoters of the BRE and RNF-7 genes, leading to the negative regulation of these two anti-apoptotic genes. Furthermore, the induction of apoptosis by cisplatin is mediated by TR3, and knockdown of TR3 reduces cisplatin-induced apoptosis in colon cancer cells by 27%. The role of TR3 in cisplatin chemotherapy is further clarified in mouse models. In Apc(min/+) mice, cisplatin inhibits intestinal tumorigenesis by 70% in a TR3 phosphorylation-dependent manner; however, the loss of TR3 function in Apc(min/+)/TR3(-/-) mice leads to the failure of cisplatin-induced repression of tumorigenesis. Consistently, xenografts derived from TR3 knockdown colon cancer cells are insensitive to cisplatin treatment, whereas a significant curative effect (50% inhibition) is observed in xenografts with functional TR3. Taken together, our study reveals a novel cross talk between Chk2 and TR3 and sheds light on the mechanism of cisplatin-induced apoptosis through TR3. Therefore, TR3 may be a new target of cisplatin for colon cancer therapy.     

Calmodulin antagonists promote TRA-8 therapy of resistant pancreatic cancer

Pancreatic cancer is highly malignant with limited therapy and a poor prognosis. TRAIL-activating therapy has been promising, however, clinical trials have shown resistance and limited responses of pancreatic cancers. We investigated the effects of calmodulin(CaM) antagonists, trifluoperazine(TFP) and tamoxifen(TMX), on TRA-8-induced apoptosis and tumorigenesis of TRA-8-resistant pancreatic cancer cells, and underlying mechanisms. TFP or TMX alone did not induce apoptosis of resistant PANC-1 cells, while they dose-dependently enhanced TRA-8-induced apoptosis. TMX treatment enhanced efficacy of TRA-8 therapy on tumorigenesis in vivo. Analysis of TRA-8-induced death-inducing-signaling-complex (DISC) identified recruitment of survival signals, CaM/Src, into DR5-associated DISC, which was inhibited by TMX/TFP. In contrast, TMX/TFP increased TRA-8-induced DISC recruitment/activation of caspase-8. Consistently, caspase-8 inhibition blocked the effects of TFP/TMX on TRA-8-induced apoptosis. Moreover, TFP/TMX induced DR5 expression. With a series of deletion/point mutants, we identified CaM antagonist-responsive region in the putative Sp1-binding domain between −295 to −300 base pairs of DR5 gene. Altogether, we have demonstrated that CaM antagonists enhance TRA-8-induced apoptosis of TRA-8-resistant pancreatic cancer cells by increasing DR5 expression and enhancing recruitment of apoptotic signal while decreasing survival signals in DR5-associated DISC. Our studies support the use of these readily available CaM antagonists combined with TRAIL-activating agents for pancreatic cancer therapy.     

Genomic and proteomic analysis reveals a threshold level of MYC required for tumor maintenance

MYC overexpression has been implicated in the pathogenesis of most types of human cancers. MYC is likely to contribute to tumorigenesis by its effects on global gene expression. Previously, we have shown that the loss of MYC overexpression is sufficient to reverse tumorigenesis. Here, we show that there is a precise threshold level of MYC expression required for maintaining the tumor phenotype, whereupon there is a switch from a gene expression program of proliferation to a state of proliferative arrest and apoptosis. Oligonucleotide microarray analysis and quantitative PCR were used to identify changes in expression in 3,921 genes, of which 2,348 were down-regulated and 1,573 were up-regulated. Critical changes in gene expression occurred at or near the MYC threshold, including genes implicated in the regulation of the G(1)-S and G(2)-M cell cycle checkpoints and death receptor/apoptosis signaling. Using two-dimensional protein analysis followed by mass spectrometry, phospho-flow fluorescence-activated cell sorting, and antibody arrays, we also identified changes at the protein level that contributed to MYC-dependent tumor regression. Proteins involved in mRNA translation decreased below threshold levels of MYC. Thus, at the MYC threshold, there is a loss of its ability to maintain tumorigenesis, with associated shifts in gene and protein expression that reestablish cell cycle checkpoints, halt protein translation, and promote apoptosis.     

肾癌中调节性细胞死亡的新动向和未来展望

肾癌是泌尿系统常见的恶性肿瘤之一。近年来,我国肾癌的发病率呈逐年上升的趋势,严重威胁着人们的健康。调节性细胞死亡是由一种细胞主动有序的死亡方式,普遍存在于生命活动过程中,在维系生命活动的平衡中发挥着至关重要的作用。近期Science杂志上报道了一种新的调节性细胞死亡方式即铜死亡,进一步强化了生命体中细胞死亡的重要性。随着对调节性细胞死亡认识的不断深入,越来越多的研究显示不同的调节性细胞死亡（如铁死亡、焦亡、自噬等）均与肾癌的发生、发展密切相关。如诱导细胞铁死亡将显著抑制肾癌的侵袭和转移、并与肾癌患者的更好预后密切相关;细胞焦亡不仅可以诱导肾癌细胞死亡还可以激活抗肾癌的免疫应答;自噬在肾癌中具有“双向”作用,增强自噬可抑制肾癌细胞生长,但也可能减弱联合用药治疗的效果;抑制细胞凋亡和坏死性凋亡可以显著促进肾癌细胞的增殖、侵袭等。本文将综述铁死亡、细胞焦亡、自噬、细胞凋亡和坏死性凋亡的分子机制和在肾癌发生、发展中作用的研究进展并进行展望,为探索肾癌的发病机制和潜在的治疗靶点提供新的视角。     

AHR与肿瘤发生发展相关性的研究进展

肿瘤发生发展的影响因素众多，其中芳香烃受体（Aryl hydrocarbon receptor,AHR）作为一种配体依赖性激活的转录因子在肿瘤细胞的增殖和凋亡中起着一定的调控作用，与肿瘤的发生发展具有密切关联。本文对近年来芳香烃受体在肿瘤发生发展中的相关研究做一综述，旨在为研究肿瘤发生机制提供一定的参考价值。     

Benzophenone-3 promotion of mammary tumorigenesis is diet-dependent

Benzophenone-3 is a putative endocrine disrupting chemical and common ingredient in sunscreens. The potential of endocrine disrupting chemicals to act as agonists or antagonists in critical hormonally regulated processes, such as mammary gland development and mammary tumorigenesis, demands evaluation of its potential in promoting breast cancer. This study identifies the effects of BP-3 on mammary tumorigenesis with high-fat diet during puberty versus adulthood in Trp53-null transplant BALB/c mice. Benzophenone-3 exposure yielded levels in urine similar to humans subjected to heavy topical sunscreen exposure. Benzophenone-3 was protective for epithelial tumorigenesis in mice fed lifelong low-fat diet, while promotional for epithelial tumorigenesis in mice fed adult high-fat diet. Benzophenone-3 increased tumor cell proliferation, decreased tumor cell apoptosis, and increased tumor vascularity dependent on specific dietary regimen and tumor histopathology. Even in instances of an ostensibly protective effect, other parameters suggest greater risk. Although benzophenone-3 seemed protective on low-fat diet, spindle cell tumors arising in these mice showed increased proliferation and decreased apoptosis. This points to a need for further studies of benzophenone-3 in both animal models and humans as a potential breast cancer risk factor, as well as a more general need to evaluate endocrine disrupting chemicals in varying dietary contexts.     

Conditional ablation of C/EBP beta demonstrates its keratinocyte-specific requirement for cell survival and mouse skin tumorigenesis

The CCAAT/enhancer binding protein beta (C/EBP beta) is implicated in the regulation of many different molecular and physiological processes. Mice with a germline deletion of C/EBP beta (C/EBP beta(-/-)) display phenotypes in a multitude of cell types and organ systems, including skin where C/EBP beta(-/-) mice exhibit increased apoptosis in epidermal keratinocytes in response to carcinogen treatment and are completely resistant to carcinogen-induced skin tumorigenesis. To determine the contribution of systemic versus cell autonomous functions of C/EBP beta to specific phenotypes, mice with a conditional 'floxed' C/EBP beta null allele were generated. Epidermal-specific deletion of C/EBP beta was achieved by Cre recombinase expression from a keratin 5 (K5) promoter. Similar to C/EBP beta(-/-) mice, K5-Cre;C/EBP beta(fl/fl) mice were completely refractory to 7,12 dimethylbenz[a]anthracene (DMBA)-induced skin tumorigenesis and these mice displayed increased DMBA-induced apoptosis in epidermal keratinocytes compared to wild-type mice. In contrast, mice lacking the related gene, C/EBP delta, were not resistant to DMBA-induced skin tumorigenesis, indicating a unique role of C/EBP beta in skin tumor development. Our findings demonstrate that C/EBP beta exerts an essential, keratinocyte-intrinsic role in cell survival in response to carcinogen treatment and the elimination of C/EBP beta in keratinocytes is sufficient to confer complete resistance of the skin to chemical carcinogenesis.