Hypoxia activates SREBP2 through Golgi disassembly in bone marrow-derived monocytes for enhanced tumor growth.

Bone marrow-derived cells (BMDCs) infiltrate hypoxic tumors at a pre-angiogenic state and differentiate into mature macrophages, thereby inducing pro-tumorigenic immunity. A critical factor regulating this differentiation is activation of SREBP2-a well-known transcription factor participating in tumorigenesis progression-through unknown cellular mechanisms. Here, we show that hypoxia-induced Golgi disassembly and Golgi-ER fusion in monocytic myeloid cells result in nuclear translocation and activation of SREBP2 in a SCAP-independent manner. Notably, hypoxia-induced SREBP2 activation was only observed in an immature lineage of bone marrow-derived cells. Single-cell RNA-seq analysis revealed that SREBP2-mediated cholesterol biosynthesis was upregulated in HSCs and monocytes but not in macrophages in the hypoxic bone marrow niche. Moreover, inhibition of cholesterol biosynthesis impaired tumor growth through suppression of pro-tumorigenic immunity and angiogenesis. Thus, our findings indicate that Golgi-ER fusion regulates SREBP2-mediated metabolic alteration in lineage-specific BMDCs under hypoxia for tumor progression.

Increased expression of histone demethylase JHDM1D under nutrient starvation suppresses tumor growth via down-regulating angiogenesis.

Histone demethylase JHDM1D (also known as KDM7A) modifies the level of methylation in histone and participates in epigenetic gene regulation; however, the role of JHDM1D in tumor progression is unknown. Here, we show that JHDM1D plays a tumor-suppressive role by regulating angiogenesis. Expression of JHDM1D was increased in mouse and human cancer cells under long-term nutrient starvation in vitro. Expression of JHDM1D mRNA was increased within avascular tumor tissue at the preangiogenic switch, along with increased expression of angiogenesis-regulating genes such as Vegf-A. Stable expression of JHDM1D cDNA or siRNA silencing of JHDM1D in cancer cells did not affect cell proliferation, anchorage-independent cell growth, or cell cycle progression in vitro. Notably, JHDM1D-expressing mouse melanoma (B16) and human cervical carcinoma (HeLa) cells exhibited significantly slower tumor growth in vivo compared with the original cells. This reduction in tumor growth was associated with decreased formation of CD31(+) blood vessels and reduced infiltration of CD11b(+) macrophage linage cells into tumor tissues. Expression of multiple angiogenic factors such as VEGF-B and angiopoietins was decreased in tumor xenografts of JHDM1D-expressing B16 and HeLa cells. Our results provide evidence that increased JHDM1D expression suppressed tumor growth by down-regulating angiogenesis under nutrient starvation.

HIF-2α suppresses p53 to enhance the stemness and regenerative potential of human embryonic stem cells.

Human embryonic stem cells (hESCs) have been reported to exert cytoprotective activity in the area of tissue injury. However, hypoxia/oxidative stress prevailing in the area of injury could activate p53, leading to death and differentiation of hESCs. Here we report that when exposed to hypoxia/oxidative stress, a small fraction of hESCs, namely the SSEA3+/ABCG2+ fraction undergoes a transient state of reprogramming to a low p53 and high hypoxia inducible factor (HIF)-2α state of transcriptional activity. This state can be sustained for a period of 2 weeks and is associated with enhanced transcriptional activity of Oct-4 and Nanog, concomitant with high teratomagenic potential. Conditioned medium obtained from the post-hypoxia SSEA3+/ABCG2+ hESCs showed cytoprotection both in vitro and in vivo. We termed this phenotype as the "enhanced stemness" state. We then demonstrated that the underlying molecular mechanism of this transient phenotype of enhanced stemness involved high Bcl-2, fibroblast growth factor (FGF)-2, and MDM2 expression and an altered state of the p53/MDM2 oscillation system. Specific silencing of HIF-2α and p53 resisted the reprogramming of SSEA3+/ABCG2+ to the enhanced stemness phenotype. Thus, our studies have uncovered a unique transient reprogramming activity in hESCs, the enhanced stemness reprogramming where a highly cytoprotective and undifferentiated state is achieved by transiently suppressing p53 activity. We suggest that this transient reprogramming is a form of stem cell altruism that benefits the surrounding tissues during the process of tissue regeneration.

Acidic extracellular pH drives accumulation of N1-acetylspermidine and recruitment of protumor neutrophils.

An acidic tumor microenvironment plays a critical role in tumor progression. However, understanding of metabolic reprogramming of tumors in response to acidic extracellular pH has remained elusive. Using comprehensive metabolomic analyses, we demonstrated that acidic extracellular pH (pH 6.8) leads to the accumulation of N1-acetylspermidine, a protumor metabolite, through up-regulation of the expression of spermidine/spermine acetyltransferase 1 (SAT1). Inhibition of SAT1 expression suppressed the accumulation of intra- and extracellular N1-acetylspermidine at acidic pH. Conversely, overexpression of SAT1 increased intra- and extracellular N1-acetylspermidine levels, supporting the proposal that SAT1 is responsible for accumulation of N1-acetylspermidine. While inhibition of SAT1 expression only had a minor effect on cancer cell growth in vitro, SAT1 knockdown significantly decreased tumor growth in vivo, supporting a contribution of the SAT1-N1-acetylspermidine axis to protumor immunity. Immune cell profiling revealed that inhibition of SAT1 expression decreased neutrophil recruitment to the tumor, resulting in impaired angiogenesis and tumor growth. We showed that antineutrophil-neutralizing antibodies suppressed growth in control tumors to a similar extent to that seen in SAT1 knockdown tumors in vivo. Further, a SAT1 signature was found to be correlated with poor patient prognosis. Our findings demonstrate that extracellular acidity stimulates recruitment of protumor neutrophils via the SAT1-N1-acetylspermidine axis, which may represent a metabolic target for antitumor immune therapy.

RACK1 regulates VEGF/Flt1-mediated cell migration via activation of a PI3K/Akt pathway.

Vascular endothelial growth factor (VEGF) is vital to physiological as well as pathological angiogenesis, and regulates a variety of cellular functions, largely by activating its 2 receptors, fms-like tyrosine kinase (Flt1) and kinase domain receptor (KDR). KDR plays a critical role in the proliferation of endothelial cells by controlling VEGF-induced phospholipase Cγ-protein kinase C (PLCγ-PKC) signaling. The function of Flt1, however, remains to be clarified. Recent evidence has indicated that Flt1 regulates the VEGF-triggered migration of endothelial cells and macrophages. Here, we show that RACK1, a ubiquitously expressed scaffolding protein, functions as an important regulator of this process. We found that RACK1 (receptor for activated protein kinase C 1) binds to Flt1 in vitro. When the endogenous expression of RACK1 was attenuated by RNA interference, the VEGF-driven migration was remarkably suppressed whereas the proliferation was unaffected in a stable Flt1-expressing cell line, AG1-G1-Flt1. Further, we demonstrated that the VEGF/Flt-mediated migration of AG1-G1-Flt1 cells occurred mainly via the activation of the PI3 kinase (PI3K)/Akt and Rac1 pathways, and that RACK1 plays a crucial regulatory role in promoting PI3K/Akt-Rac1 activation.

Downregulation of receptor for activated C-kinase 1 (RACK1) suppresses tumor growth by inhibiting tumor cell proliferation and tumor-associated angiogenesis.

By behaving as molecular hubs, scaffold proteins can assemble a large number of signaling molecules and organize complicated intracellular signaling networks in time and space. Owing to their crucial role in mediating intracellular signaling related to tumor cell growth and migration, recent studies have highlighted the relevance of scaffold proteins in human cancers and indicated that interfering with their expression and/or their ability to bind effector proteins can inhibit cancer progression. Here, we show that receptor for activated C-kinase 1 (RACK1), a ubiquitously expressed scaffolding protein, plays a crucial regulatory role in tumor growth. Using an RNA silencing approach, we found that downregulation of RACK1 expression in HeLa and A673 tumor cells markedly suppressed the proliferation and invasion of these cells in vitro and tumor development in vivo. Consequently, we found that significant suppression of constitutive phosphorylation of Akt and MAPK by RACK1 silencing may contribute to the inhibition of tumor growth. Moreover, RACK1 silencing significantly attenuated tumor-associated angiogenesis by, at least in part, inhibiting the expression of two critical angiogenic factors, namely vascular endothelial growth factor-B and fibroblast growth factor 2. The results of the present study show that RACK1 is a potent enhancer of tumor growth and, thus, a potential anti-cancer therapeutic target.

Hypoxia enhances tumor stemness by increasing the invasive and tumorigenic side population fraction.

Although advances have been made in understanding the role of hypoxia in the stem cell niche, almost nothing is known about a potentially similar role of hypoxia in maintaining the tumor stem cell (TSC) niche. Here we show that a highly tumorigenic fraction of side population (SP) cells is localized in the hypoxic zones of solid tumors in vivo. We first identified a highly migratory, invasive, and tumorigenic fraction of post-hypoxic side population cells (SPm([hox]) fraction) in a diverse group of solid tumor cell lines, including neuroblastoma, rhabdomyosarcoma, and small-cell lung carcinoma. To identify the SPm((hox)) fraction, we used an "injured conditioned medium" derived from bone marrow stromal cells treated with hypoxia and oxidative stress. We found that a highly tumorigenic SP fraction migrates to the injured conditioned medium in a Boyden chamber. We show that as few as 100 SPm((hox)) cells form rapidly growing tumors in vivo. In vitro exposure to hypoxia increases the SPm((hox)) fraction significantly. Quantitative real-time polymerase chain reaction and immunofluorescence studies showed that SPm((hox)) cells expressed Oct-4, a "stemness" gene having a potential role in TSC maintenance. In nude mice xenografts, SPm((hox)) cells were localized to the hypoxic zones, as demonstrated after quantum dot labeling. These results suggest that a highly tumorigenic SP fraction migrates to the area of hypoxia; this migration is similar to the migration of normal bone marrow SP fraction to the area of injury/hypoxia. Furthermore, the hypoxic microenvironment may serve as a niche for the highly tumorigenic fraction of SP cells.

Phosphoethanolamine Accumulation Protects Cancer Cells under Glutamine Starvation through Downregulation of PCYT2.

Tolerance to severe tumor microenvironments, including hypoxia and nutrient starvation, is a common feature of aggressive cancer cells and can be targeted. However, metabolic alterations that support cancer cells upon nutrient starvation are not well understood. Here, by comprehensive metabolome analyses, we show that glutamine deprivation leads to phosphoethanolamine (PEtn) accumulation in cancer cells via the downregulation of PEtn cytidylyltransferase (PCYT2), a rate-limiting enzyme of phosphatidylethanolamine biosynthesis. PEtn accumulation correlated with tumor growth under nutrient starvation. PCYT2 suppression was partially mediated by downregulation of the transcription factor ELF3. Furthermore, PCYT2 overexpression reduced PEtn levels and tumor growth. In addition, PEtn accumulation and PCYT2 downregulation in human breast tumors correlated with poor prognosis. Thus, we show that glutamine deprivation leads to tumor progression by regulating PE biosynthesis via the ELF3-PCYT2 axis. Furthermore, manipulating glutamine-responsive genes could be a therapeutic approach to limit cancer progression.

A hypoxia-driven vascular endothelial growth factor/Flt1 autocrine loop interacts with hypoxia-inducible factor-1alpha through mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2 pathway in neuroblastoma.

Flt1, an "fms-like tyrosine kinase" receptor, has been suggested to play an active role in vascular endothelial growth factor (VEGF)-mediated autocrine signaling of tumor growth and angiogenesis. Here, we used a neuroblastoma model to investigate the role of VEGF/Flt1 signaling in hypoxia-mediated tumor cell survival, drug resistance, and in vivo angiogenesis. SK-N-BE2, a highly malignant neuroblastoma cell line resistant to hypoxia-induced apoptosis expresses active Flt1 but lacks VEGFR2 expression. We found that 24-hour hypoxia (<0.1% O2) alone (no serum deprivation) showed sustained activation of extracellular signal-regulated kinase 1/2 (ERK1/2) associated with bcl-2 up-regulation and resistance to etoposide-induced (5 mumol/L) apoptosis. Treatment with anti-VEGF and anti-Flt1 antibodies inhibited ERK1/2 activation, down-regulated bcl-2, and reversed the hypoxia-mediated drug resistance to etoposide. Similar results were obtained with U0126 and ursolic acid, specific and nonspecific inhibitors of ERK1/2, respectively. We confirmed the protective role of Flt1 receptor by small interfering RNA knockout and Flt1 overexpression studies. Subsequently, we found that inhibition of VEGF/Flt1 autocrine signaling led to reduced hypoxia-inducible factor-1alpha (HIF-1alpha) phosphorylation. Furthermore, the reduced phosphorylation was associated with down-regulation of basic fibroblast growth factor, a downstream target of the HIF-1alpha and VEGF pathways. Our findings suggested an expanded autocrine loop between VEGF/Flt1 signaling and HIF-1alpha. We investigated the angiogenic activity of the loop in an in vivo Matrigel plug assay. The hypoxia-treated conditioned medium induced a strong angiogenic response, as well as the cooption of surrounding vessels into the plugs; ursolic acid inhibited the angiogenesis process. We also found that three other Flt1-expressing neuroblastoma cell lines show hypoxia-mediated drug resistance to etoposide, melphalan, doxorubicin, and cyclophosphamide. Taken together, we conclude that a hypoxia-driven VEGF/Flt1 autocrine loop interacts with HIF-1alpha through a mitogen-activated protein kinase/ERK1/2 pathway in neuroblastoma. The interaction, in the form of an autocrine loop, is required for the hypoxia-driven cell survival, drug resistance, and angiogenesis in neuroblastoma.

Loss of DNA Damage Response in Neuroblastoma and Utility of a PARP Inhibitor.

Background: Neuroblastoma (NB) is the most common solid tumor found in children, and deletions within the 11q region are observed in 11% to 48% of these tumors. Notably, such tumors are associated with poor prognosis; however, little is known regarding the molecular targets located in 11q. Methods: Genomic alterations of ATM , DNA damage response (DDR)-associated genes located in 11q ( MRE11A, H2AFX , and CHEK1 ), and BRCA1, BARD1, CHEK2, MDM2 , and TP53 were investigated in 45 NB-derived cell lines and 237 fresh tumor samples. PARP (poly [ADP-ribose] polymerase) inhibitor sensitivity of NB was investigated in in vitro and invivo xenograft models. All statistical tests were two-sided. Results: Among 237 fresh tumor samples, ATM, MRE11A, H2AFX , and/or CHEK1 loss or imbalance in 11q was detected in 20.7% of NBs, 89.8% of which were stage III or IV. An additional 7.2% contained ATM rare single nucleotide variants (SNVs). Rare SNVs in DDR-associated genes other than ATM were detected in 26.4% and were mutually exclusive. Overall, samples with SNVs and/or copy number alterations in these genes accounted for 48.4%. ATM-defective cells are known to exhibit dysfunctions in homologous recombination repair, suggesting a potential for synthetic lethality by PARP inhibition. Indeed, 83.3% NB-derived cell lines exhibited sensitivity to PARP inhibition. In addition, NB growth was markedly attenuated in the xenograft group receiving PARP inhibitors (sham-treated vs olaprib-treated group; mean [SD] tumor volume of sham-treated vs olaprib-treated groups = 7377 [1451] m 3 vs 298 [312] m 3 , P = .001, n = 4). Conclusions: Genomic alterations of DDR-associated genes including ATM, which regulates homologous recombination repair, were observed in almost half of NBs, suggesting that synthetic lethality could be induced by treatment with a PARP inhibitor. Indeed, DDR-defective NB cell lines were sensitive to PARP inhibitors. Thus, PARP inhibitors represent candidate NB therapeutics.

Vascular endothelial growth factor acts in an autocrine manner in rhabdomyosarcoma cell lines and can be inhibited with all-trans-retinoic acid.

Vascular endothelial growth factor (VEGF) is a potent signalling molecule that acts through two tyrosine kinase receptors, VEGFR1 and VEGFR2. The upregulation of VEGF and its receptors is important in tumour-associated angiogenesis; however, recent studies suggest that several tumour cells express VEGF receptors and may be influenced by autocrine VEGF signalling. Rhabdomyosarcoma (RMS) is the most common paediatric soft-tissue sarcoma, and is dependent on autocrine signalling for its growth. The alveolar subtype of RMS is often characterized by the presence of a PAX3-FKHR translocation, and when introduced into non-RMS cells, the resultant fusion protein induces expression of VEGFR1. In our study, we examined the expression of VEGF and its receptors in RMS, and autocrine effects of VEGF on cell growth. VEGF and receptor mRNA and protein were found to be expressed in RMS cells. Exogenous VEGF addition resulted in extracellular signal-regulated kinase-1/2 phosphorylation and cell proliferation, and both were reduced by VEGFR1 blockade. Growth was also slowed by VEGFR1 inhibitor alone. Treatment of RMS cells with all-trans-retinoic acid decreased VEGF secretion and slowed cell growth, which was rescued by VEGF. These data suggest that autocrine VEGF signalling likely influences RMS growth and its inhibition may be an effective treatment for RMS.

Detection of ATM gene mutation in human glioma cell line M059J by a rapid frameshift/stop codon assay in yeast.

A yeast-based frameshift/stop codon assay for examining ATM (ataxia telangiectasia mutated) mutations was established. Each of six fragments of a PCR-amplified coding sequence for ATM is inserted in frame by homologous recombination into a yeast URA3 fusion protein gene, and the transformants are assayed for growth in the absence of uracil. The usefulness of this assay was verified in a panel of cell lines derived from individuals with homozygous and heterozygous ATM mutations. The assay was also shown to distinguish between specimens with wild-type alleles and those with truncating mutations: a frameshift mutation or an inserted stop codon. Using this assay M059J cells, which fail to express the catalytic subunit of DNA-dependent protein kinase (PRKDC, also known as DNA-PKcs) and are hypersensitive to ionizing radiation, were found to express two different aberrant ATM transcripts: one characterized by 4776 del 133, which corresponds to the deletion of exon 33, and the other by 4909 ins 116. Subsequent analysis of the intron sequences revealed that 4909 ins 116 is comprised of a nucleotide sequence corresponding to 84013-84128 in intron 33 with a cryptic splice site. Thus the radiosensitive phenotype of M059J cells appears to be due to a defect in PRKDC and a truncating ATM mutation.

Inhibition of histone demethylase JMJD1A improves anti-angiogenic therapy and reduces tumor-associated macrophages.

Antiangiogenic strategies can be effective for cancer therapy, but like all therapies resistance poses a major clinical challenge. Hypoxia and nutrient starvation select for aggressive qualities that may render tumors resistant to antiangiogenic attack. Here, we show that hypoxia and nutrient starvation cooperate to drive tumor aggressiveness through epigenetic regulation of the histone demethylase JMJD1A (JHDM2A; KDM3A). In cancer cells rendered resistant to long-term hypoxia and nutrient starvation, we documented a stimulation of AKT phosphorylation, cell morphologic changes, cell migration, invasion, and anchorage-independent growth in culture. These qualities associated in vivo with increased angiogenesis and infiltration of macrophages into tumor tissues. Through expression microarray analysis, we identified a cluster of functional drivers such as VEGFA, FGF18, and JMJD1A, the latter which was upregulated in vitro under conditions of hypoxia and nutrient starvation and in vivo before activation of the angiogenic switch or the prerefractory phase of antiangiogenic therapy. JMJD1A inhibition suppressed tumor growth by downregulating angiogenesis and macrophage infiltration, by suppressing expression of FGF2, HGF, and ANG2. Notably, JMJD1A inhibition enhanced the antitumor effects of the anti-VEGF compound bevacizumab and the VEGFR/KDR inhibitor sunitinib. Our results form the foundation of a strategy to attack hypoxia- and nutrient starvation-resistant cancer cells as an approach to leverage antiangiogenic treatments and limit resistance to them.

Squalene selectively protects mouse bone marrow progenitors against cisplatin and carboplatin-induced cytotoxicity in vivo without protecting tumor growth.

Squalene, an isoprenoid antioxidant is a potential cytoprotective agent against chemotherapy-induced toxicity. We have previously published that squalene protects light-density bone marrow cells against cis-diamminedichloroplatinum( II) (cisplatin)-induced toxicity without protecting tumor cells in vitro. Here, we developed an in vivo mouse model of cisplatin and cis-diammine (cyclobutane-1,1-dicarboxylato) platinum(II) (carboplatin)-induced toxicity to further investigate squalene-mediated LD-BM cytoprotection including the molecular mechanism behind selective cytoprotection. We found that squalene significantly reduced the body weight loss of cisplatin and carboplatin-treated mice. Light-density bone marrow cells from squalene-treated mice exhibited improved formation of hematopoietic colonies (colony-forming unit-granulocyte macrophage). Furthermore, squalene also protected mesenchymal stem cell colonies (colony-forming unit-fibroblast) from cisplatin and carboplatin-induced toxicity. Squalene-induced protection was associated with decreased reactive oxygen species and increased levels of glutathione and glutathione peroxidase/glutathione-S-transferase. Importantly, squalene did not protect neuroblastoma, small cell carcinoma, or medulloblastoma xenografts against cisplatin-induced toxicity. These results suggest that squalene is a potential candidate for future development as a cytoprotective agent against chemotherapeutic toxicity.

Expression of cyclin-dependent kinase inhibitor p27/Kip1 and AP-1 coactivator p38/Jab1 correlates with differentiation of embryonal rhabdomyosarcoma.

Cyclin-dependent kinase (CDK) inhibitor p27/Kip1 (p27) is a diagnostic and prognostic marker of various malignancies. Low expression of p27 reflects poor differentiation and poor prognosis, and an inverse correlation between the expression of p27 and degree of tumor malignancy has been reported. Because p27 mutation is extremely rare in human tumors, it is important to study the expression of p27 and its inactivator, p38/Jab1 (JAB1). Here we analyzed the expression of p27 and JAB1 by immunohistochemistry in embryonal rhabdomyosarcoma (E-RMS). We first confirmed the expression of p27 and JAB1 in normal human tonsillar epithelium, and observed a coordinated expression pattern depending on cell differentiation. Subsequently, specimens of eight poorly- and three well-differentiated E-RMS were examined for the expression of p27 and JAB1. The analyses revealed that four out of eight poorly-differentiated E-RMS were negative for p27, with positivity for nuclear JAB (NJAB) (- / + for p27/NJAB) in three and negativity for any JAB-1 expression ( - / -) in one. The remaining four poorly-differentiated E-RMS expressed p27 in the nuclei, together with predominant NJAB (+ / +). In three well-differentiated E-RMS, only one expressed nuclear p27 and all of these three expressed no NJAB (+ / - for p27/NJAB), but expressed predominant cytoplasmic JAB1 (CJAB). These findings suggest that JAB1 may play an important role in determining the differentiation stage of rhabdomyosarcoma cells by modulating the activity of CDK inhibitor p27.

Immunohistochemical study of Skp2 and Jab1, two key molecules in the degradation of P27, in lung adenocarcinoma.

To clarify the association of the P27 degradation pathway proteins, Skp2 and Jab1, with the development and progression of lung adenocarcinoma (AD), we immunohistochemically investigated Skp2 and Jab1 expression together with P27- and Ki-67-labeling in 110 lung AD and 11 atypical adenomatous hyperplasia (AAH) and analyzed the relationship between the expression of these proteins and the clinicopathological factors. High Skp2 or Jab1 expression was frequent in lung AD (52/110, 47%, and 59/110, 54%, respectively), and high expression of Jab1 was also frequent in AAH (4/11, 36%), while it was not observed in normal bronchiolar epithelium. The P27 labeling index (LI) was reciprocally correlated with high Skp2 and Jab1 expression, and a higher Ki-67 LI was significantly correlated with high Skp2 and Jab1 expression. However, low P27 expression did not correlate with a higher Ki-67 LI. High Skp2 lung AD showed significant correlation with blood and lymphatic vessel invasion, which low P27 expression did not correlate with. Furthermore, high Skp2 expression in lung AD was significantly correlated with a poor outcome for patients. Thus, Skp2 and Jab1 regulate P27 degradation, and might contribute to the development and progression of lung AD through P27-mediated and -unmediated mechanisms.

Missense mutation and defective function of ATM in a childhood acute leukemia patient with MLL gene rearrangement.

The possible involvement of germline mutation of the ataxia telangiectasia mutated (ATM) gene in childhood acute leukemia with mixed lineage leukemia (MLL) gene rearrangement (MLL(+)) was investigated. Of the 7 patients studied, 1 showed a germline missense ATM mutation (8921C>T; Pro2974Leu), located in the phosphatidylinositol-3 (PI-3) kinase domain. In reconstitution assays, the ATM mutant 8921T could only partially rescue the radiosensitive phenotype of AT fibroblasts, and in an in vitro kinase assay, it showed a defective phosphorylation of p53-Ser15. Furthermore, the introduction of 8921T in U2OS cells, characterized by a normal ATM/p53 signal transduction, caused a significant reduction of in vivo p53-Ser15 phosphorylation, suggesting a dominant-negative effect of the mutant ATM over the wild-type protein. Our finding in this patient suggests that altered function of ATM plays some pathogenic roles in the development of MLL(+) leukemia.

Identification and characterization of polymorphic variations of the ataxia telangiectasia mutated (ATM) gene in childhood Hodgkin disease.

There are conflicting reports about the involvement of single nucleotide polymorphisms (SNPs) of the ataxia telangiectasia mutated (ATM) gene with cancer, and the consequences of these SNPs for ATM function remain unclear. We therefore sought to identify SNPs of the ATM gene in pediatric Hodgkin disease (HD) and to analyze ATM function in cells from patients with these SNPs. We have identified SNPs of the ATM gene in 5 of 14 children (S1455R, n = 1; H1380Y, n = 1; N1650S, n = 2; and I709I, n = 1). One patient had nonsense-associated altered splicing of the ATM gene. Lymphoblastoid cell lines expressing the S1455R and N1650S exhibited defective ATM-mediated p53 phosphorylation and Chk2 activation; cells expressing the H1380Y exhibited defective c-Abl activation after X-irradiation. Expression of the N1650S in ATM-null fibroblasts conferred only partial hyperradiosensitivity. Furthermore, the introduction of N1650S ATM into U2OS cells, which express wild-type ATM, showed reduced p53-Ser15 phosphorylation, suggesting a dominant-negative effect of the N1650S over the wild-type ATM protein. We conclude that the rare polymorphic variants of the ATM gene that we identified in children with HD encode functionally abnormal proteins, and we discuss the possible genetic risk factors for childhood HD.