Copper chelation suppresses epithelial-mesenchymal transition by inhibition of canonical and non-canonical TGF-β signaling pathways in cancer

BACKGROUND

Metastatic cancer cells exploit Epithelial-mesenchymal-transition (EMT) to enhance their migration, invasion, and resistance to treatments. Recent studies highlight that elevated levels of copper are implicated in cancer progression and metastasis. Clinical trials using copper chelators are associated with improved patient survival; however, the molecular mechanisms by which copper depletion inhibits tumor progression and metastasis are poorly understood. This remains a major hurdle to the clinical translation of copper chelators. Here, we propose that copper chelation inhibits metastasis by reducing TGF-β levels and EMT signaling. Given that many drugs targeting TGF-β have failed in clinical trials, partly because of severe side effects arising in patients, we hypothesized that copper chelation therapy might be a less toxic alternative to target the TGF-β/EMT axis.

RESULTS

Our cytokine array and RNA-seq data suggested a link between copper homeostasis, TGF-β and EMT process. To validate this hypothesis, we performed single-cell imaging, protein assays, and in vivo studies. Here, we used the copper chelating agent TEPA to block copper trafficking. Our in vivo study showed a reduction of TGF-β levels and metastasis to the lung in the TNBC mouse model. Mechanistically, TEPA significantly downregulated canonical (TGF-β/SMAD2&3) and non-canonical (TGF-β/PI3K/AKT, TGF-β/RAS/RAF/MEK/ERK, and TGF-β/WNT/β-catenin) TGF-β signaling pathways. Additionally, EMT markers of MMP-9, MMP-14, Vimentin, β-catenin, ZEB1, and p-SMAD2 were downregulated, and EMT transcription factors of SNAI1, ZEB1, and p-SMAD2 accumulated in the cytoplasm after treatment.

CONCLUSIONS

Our study suggests that copper chelation therapy represents a potentially effective therapeutic approach for targeting TGF-β and inhibiting EMT in a diverse range of cancers.

Abstract 2127: SSB1 is essential for embryogenesis and maintenance of genomic stability in mice

Single-stranded DNA binding proteins (SSBs) are essential for multiple DNA transactions, including regulation of DNA damage checkpoints and repair of DNA damage. Previously, we reported the functional characterization of these proteins in human cells using specific siRNA and provided the initial evidence that both SSBs are essential for efficient repair of DNA double strand breaks by the homologous recombinational repair pathway, and for efficient initiation of the ATM/ATR dependent signaling pathway (Richard et al., 2008). However cellular model systems have inherent limitations. To decipher the role of these newly identified proteins at the organismal level, we have generated conditional SSB1 and SSB2 knockout (KO) mouse models. The constitutive SSB1 KO mice show late embryonic lethality and die perinatally. The conditional inactivation of SSB1 in adult mice is associated with testicular atrophy, reduced fertility and increased genomic instability. We also find compensatory up-regulation of SSB2 protein levels in multiple tissues of conditional SSB1 KO mice. In addition, we report increased radiosensitiity of SSB1-/- mice in response to ionizing radiation, and increased genomic instability, which manifests as a broad spectrum of tumours at approximately 1 year of age. T cells isolated from these animals exhibited mild G1/S and G2/M checkpoint defects, and a persistence of DNA damage as seen by increased gamma-H2AX and 53BP1 foci in response to α-irradiation. Collectively, these results demonstrate an essential role of SSB1 in the maintenance of genomic stability in-vivo. Reference Richard, DJ., Bolderson, E., —et al. Khanna KK (2008). Single-stranded DNA binding protein is critical for genomic stability. Nature 453: 677-681

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2127. doi:1538-7445.AM2012-2127

No evidence for association of ataxia-telangiectasia mutated gene T2119C and C3161G amino acid substitution variants with risk of breast cancer

BACKGROUND

There is evidence that certain mutations in the double-strand break repair pathway ataxia-telangiectasia mutated gene act in a dominant-negative manner to increase the risk of breast cancer. There are also some reports to suggest that the amino acid substitution variants T2119C Ser707Pro and C3161G Pro1054Arg may be associated with breast cancer risk. We investigate the breast cancer risk associated with these two nonconservative amino acid substitution variants using a large Australian population-based case-control study.

METHODS

The polymorphisms were genotyped in more than 1300 cases and 600 controls using 5' exonuclease assays. Case-control analyses and genotype distributions were compared by logistic regression.

RESULTS

The 2119C variant was rare, occurring at frequencies of 1.4 and 1.3% in cases and controls, respectively (P = 0.8). There was no difference in genotype distribution between cases and controls (P = 0.8), and the TC genotype was not associated with increased risk of breast cancer (adjusted odds ratio = 1.08, 95% confidence interval = 0.59-1.97, P = 0.8). Similarly, the 3161G variant was no more common in cases than in controls (2.9% versus 2.2%, P = 0.2), there was no difference in genotype distribution between cases and controls (P = 0.1), and the CG genotype was not associated with an increased risk of breast cancer (adjusted odds ratio = 1.30, 95% confidence interval = 0.85-1.98, P = 0.2). This lack of evidence for an association persisted within groups defined by the family history of breast cancer or by age.

CONCLUSION

The 2119C and 3161G amino acid substitution variants are not associated with moderate or high risks of breast cancer in Australian women.

Chk2 activation dependence on Nbs1 after DNA damage

The checkpoint kinase Chk2 has a key role in delaying cell cycle progression in response to DNA damage. Upon activation by low-dose ionizing radiation (IR), which occurs in an ataxia telangiectasia mutated (ATM)-dependent manner, Chk2 can phosphorylate the mitosis-inducing phosphatase Cdc25C on an inhibitory site, blocking entry into mitosis, and p53 on a regulatory site, causing G(1) arrest. Here we show that the ATM-dependent activation of Chk2 by gamma- radiation requires Nbs1, the gene product involved in the Nijmegen breakage syndrome (NBS), a disorder that shares with AT a variety of phenotypic defects including chromosome fragility, radiosensitivity, and radioresistant DNA synthesis. Thus, whereas in normal cells Chk2 undergoes a time-dependent increased phosphorylation and induction of catalytic activity against Cdc25C, in NBS cells null for Nbs1 protein, Chk2 phosphorylation and activation are both defective. Importantly, these defects in NBS cells can be complemented by reintroduction of wild-type Nbs1, but neither by a carboxy-terminal deletion mutant of Nbs1 at amino acid 590, unable to form a complex with and to transport Mre11 and Rad50 in the nucleus, nor by an Nbs1 mutated at Ser343 (S343A), the ATM phosphorylation site. Chk2 nuclear expression is unaffected in NBS cells, hence excluding a mislocalization as the cause of failed Chk2 activation in Nbs1-null cells. Interestingly, the impaired Chk2 function in NBS cells correlates with the inability, unlike normal cells, to stop entry into mitosis immediately after irradiation, a checkpoint abnormality that can be corrected by introduction of the wild-type but not the S343A mutant form of Nbs1. Altogether, these findings underscore the crucial role of a functional Nbs1 complex in Chk2 activation and suggest that checkpoint defects in NBS cells may result from the inability to activate Chk2.

ATM-dependent phosphorylation of nibrin in response to radiation exposure

Mutations in the gene ATM are responsible for the genetic disorder ataxia-telangiectasia (A-T), which is characterized by cerebellar dysfunction, radiosensitivity, chromosomal instability and cancer predisposition. Both the A-T phenotype and the similarity of the ATM protein to other DNA-damage sensors suggests a role for ATM in biochemical pathways involved in the recognition, signalling and repair of DNA double-strand breaks (DSBs). There are strong parallels between the pattern of radiosensitivity, chromosomal instability and cancer predisposition in A-T patients and that in patients with Nijmegen breakage syndrome (NBS). The protein defective in NBS, nibrin (encoded by NBS1), forms a complex with MRE11 and RAD50 (refs 1,2). This complex localizes to DSBs within 30 minutes after cellular exposure to ionizing radiation (IR) and is observed in brightly staining nuclear foci after a longer period of time. The overlap between clinical and cellular phenotypes in A-T and NBS suggests that ATM and nibrin may function in the same biochemical pathway. Here we demonstrate that nibrin is phosphorylated within one hour of treatment of cells with IR. This response is abrogated in A-T cells that either do not express ATM protein or express near full-length mutant protein. We also show that ATM physically interacts with and phosphorylates nibrin on serine 343 both in vivo and in vitro. Phosphorylation of this site appears to be functionally important because mutated nibrin (S343A) does not completely complement radiosensitivity in NBS cells. ATM phosphorylation of nibrin does not affect nibrin-MRE11-RAD50 association as revealed by radiation-induced foci formation. Our data provide a biochemical explanation for the similarity in phenotype between A-T and NBS.

Cup feeding: an alternative to bottle feeding in a neonatal intensive care unit

Cup feeding has been suggested as an alternative to bottle feeding to help promote breastfeeding by avoiding nipple confusion. To demonstrate the possibility and utility of cup feeding, records of 59 preterm and low birthweight babies (born before 37 weeks' gestation) admitted to a neonatal intensive care unit (NICU) from May 1995 to April 1996 were analyzed. Feeding was initiated on cup if swallowing was present and cup feeding was possible as early as 29 weeks' gestational age with a birthweight of 900 g. In the case of five infants (38 per cent) in the gestational age group 28-30 weeks, 19 infants (52 per cent) in the 31-34 weeks' gestation group, and six (56 per cent) in the 35-37 weeks' gestation group, feeding could be commenced directly with a cup. Out of 59 infants, 33 infants (56 per cent) could be discharged on exclusive breastfeeding. It was concluded that cup feeding is a useful alternative to bottle feeding and an effective method of feeding preterm and small infants in NICU. Cup feeding allows successful breastfeeding without causing 'nipple confusion'.

Calpain activation is upstream of caspases in radiation-induced apoptosis

The molecular events involved in apoptosis induced by ionizing radiation remain unresolved. In this paper we show that the cleavage of fodrin to a 150 kDa fragment is an early proteolytic event in radiation-induced apoptosis in the Burkitts' Lymphoma cell line BL30A and requires 100 microM zVAD-fmk for inhibition. Caspases-1, -3, -6 and -7 were shown to cleave fodrin to the 150 kDa fragment in vitro and all were inhibited by 10 microM zVAD-fmk. We also show that the in vitro cleavage of fodrin by calpain is inhibited by 100 microM zVAD-fmk as was the calpain-mediated hydrolysis of casein. We demonstrate that calpain is activated within 15 min after radiation exposure, concomitant with the cleavage of fodrin to the 150 kDa fragment whereas caspase-3 is activated at 2 h correlating with the cleavage of fodrin to the 120 kDa fragment. These results support a role for calpain in the early phases of the radiation-induced apoptosis pathway, upstream of the caspases.

Mineralocorticoid blockade reduces vascular injury in stroke-prone hypertensive rats

Chronic treatment of saline-drinking stroke-prone spontaneously hypertensive rats (SHRSP) with agents that interfere with the formation or actions of angiotensin II (Ang II) prevents the development of stroke and renal vascular damage. Ang II, in addition to its direct vascular effects, stimulates the synthesis and release of aldosterone. To assess the role of aldosterone in the development of pathologic changes in these rats, we implanted time-release pellets containing 200 mg of the mineralocorticoid receptor antagonist, spironolactone, into 14 SHRSP at 7.5 weeks of age. Eight SHRSP littermates received placebo pellets. Over the period of study (3 to 4 weeks), systolic blood pressure (SBP) was not different between the groups. Spironolactone did not enhance water and electrolyte excretion. All placebo-treated SHRSP developed marked proteinuria (150+/-6 mg/d) whereas in spironolactone-treated SHRSP, urinary protein excretion (UPE) averaged 39+/-9 mg/d (P<.0001). In a second study to assess effects on survival, 6 SHRSP received spironolactone (10 mg/kg/d) and 6 received vehicle. All but one of the control rats displayed signs of stroke and died by 16 weeks of age, while the spironolactone-treated SHRSP remained asymptomatic through 19 weeks of age (P<.03). At 16 weeks of age, spironolactone-treated SHRSP were severely hypertensive (247+/-3 mm Hg), yet UPE remained at baseline levels. In contrast, preterminal UPE averaged 136+/-13 mg/d in control rats (P<.0001). In both studies, histopathologic examination revealed a marked protective effect of spironolactone against the development of malignant nephrosclerotic and cerebrovascular lesions. These observations indicate a vascular and end organ protective effect of spironolactone in the absence of lowered blood pressure in saline-drinking SHRSP and are consistent with a major role for mineralocorticoids as hormonal mediators of vascular injury.

Distinct genetic groups of Giardia intestinalis distinguished by restriction fragment length polymorphisms

The taxonomic status of the parasitic protozoal species Giardia intestinalis depends on the morphological similarity of all Giardia isolated from humans and the presumption that Giardia are host-specific. On the basis of electrophoretic data derived from examination of 26 enzyme loci in Australian isolates, it has been proposed that G. intestinalis is a species complex comprising three or four genetically distinct (but morphologically cryptic) species. These received the tentative designations of genetic groups I-IV (R. H. Andrews, M. Adams, P. F. L. Boreham, G. Mayrhofer & B. P. Meloni. International Journal for Parasitology 19, 183-190, 1989). In the present study, two unrelated DNA probes (one specific for a gene encoding a trophozoite surface protein, the other detecting a non-coding repetitive sequence within the G. intestinalis genome) were used in Southern hybridization analyses to examine 10 axenic isolates of G. intestinalis, established from diverse geographical regions in Australia, together with the Portland-1 isolate from the USA. Both probes identified every isolate unambiguously as belonging to one or other of two genetic clusters. Electrophoretic analysis of the same samples indicated that these clusters correspond to the previously defined genetic groups I and II. No heterogeneity was apparent within the seven group I isolates using either probe. However, when probed with the repetitive sequence, the four isolates belonging to group II exhibited small differences in banding patterns, suggesting that this group may be less homogeneous than group I.(ABSTRACT TRUNCATED AT 250 WORDS)

Wheat germ agglutinin specifically inhibits formyl peptide-induced polymorphonuclear leukocyte chemotaxis

Evidence that surface membrane glycoproteins of polymorphonuclear leukocytes (PMN) are involved in stimulus-response coupling prompted us to examine effects on these cells of various plant lectins. We have found that wheat germ agglutinin (WGA) (1.0 microgram/ml) completely, specifically, and irreversibly inhibits directed migration (chemotaxis) of human PMN toward the synthetic peptide, N-formylmethionyl-leucyl-phenylalanine (FMLP) (0.1 to 100 nM). This effect of WGA was not shared by subagglutinating concentrations of either concanavalin A or Bandeirea simplicifolia lectin. In contrast to its effects on FMLP-induced chemotaxis, WGA did not influence other FMLP-induced PMN responses (i.e., selective discharge of lysosomal enzymes from cytochalasin B-treated cells, generation of superoxide anion radical(s). WGA also did not influence PMN chemotactic responses to either the complement-derived peptide, C5a, or the lipoxygenase product, leukotriene B4. Inhibition of FMLP-induced chemotaxis by WGA was not reversed by washing WGA-treated cells, but was reversed (and prevented) by N-acetyl-D-glucosamine (not by N-acetyl-D-galactosamine or mannosamine). WGA did not affect either orientation or stimulated random motility of PMN, and did not interfere with specific binding to PMN of (3H)-FMLP. A derivative of WGA with 10-fold less agglutinating activity for human erythrocytes was prepared by treating the native lectin with cyanogen bromide and formic acid. The derivative also inhibited FMLP-induced PMN chemotaxis specifically and selectively. These data suggest that WGA specifically inhibits FMLP-induced PMN chemotaxis by attaching to N-acetyl-D-glucosamine residues at a locus on the PMN plasma membrane that is distinct from the binding site of the FMLP receptor.

Wheat germ agglutinin specifically inhibits formyl peptide-induced polymorphonuclear leukocyte chemotaxis

Evidence that surface membrane glycoproteins of polymorphonuclear leukocytes (PMN) are involved in stimulus-response coupling prompted us to examine effects on these cells of various plant lectins. We have found that wheat germ agglutinin (WGA) (1.0 microgram/ml) completely, specifically, and irreversibly inhibits directed migration (chemotaxis) of human PMN toward the synthetic peptide, N-formylmethionyl-leucyl-phenylalanine (FMLP) (0.1 to 100 nM). This effect of WGA was not shared by subagglutinating concentrations of either concanavalin A or Bandeirea simplicifolia lectin. In contrast to its effects on FMLP-induced chemotaxis, WGA did not influence other FMLP-induced PMN responses (i.e., selective discharge of lysosomal enzymes from cytochalasin B-treated cells, generation of superoxide anion radical(s). WGA also did not influence PMN chemotactic responses to either the complement-derived peptide, C5a, or the lipoxygenase product, leukotriene B4. Inhibition of FMLP-induced chemotaxis by WGA was not reversed by washing WGA-treated cells, but was reversed (and prevented) by N-acetyl-D-glucosamine (not by N-acetyl-D-galactosamine or mannosamine). WGA did not affect either orientation or stimulated random motility of PMN, and did not interfere with specific binding to PMN of (3H)-FMLP. A derivative of WGA with 10-fold less agglutinating activity for human erythrocytes was prepared by treating the native lectin with cyanogen bromide and formic acid. The derivative also inhibited FMLP-induced PMN chemotaxis specifically and selectively. These data suggest that WGA specifically inhibits FMLP-induced PMN chemotaxis by attaching to N-acetyl-D-glucosamine residues at a locus on the PMN plasma membrane that is distinct from the binding site of the FMLP receptor.