The overall prognosis of acute myeloid leukemia (AML) remains dismal, largely because of the inability of current therapies to kill leukemia stem cells (LSCs) with intrinsic resistance. Loss of the stress sensor growth arrest and DNA damage-inducible 45 alpha (GADD45A) is implicated in poor clinical outcomes, but its role in LSCs and AML pathogenesis is unknown. Here, we define GADD45A as a key downstream target of G protein-coupled receptor (LGR)4 pathway and discover a regulatory role for GADD45A loss in promoting leukemia-initiating activity and oxidative resistance in LGR4/HOXA9-dependent AML, a poor prognosis subset of leukemia. Knockout of GADD45A enhances AML progression in murine and patient-derived xenograft (PDX) mouse models. Deletion of GADD45A induces substantial mutations, increases LSC self-renewal and stemness in vivo, and reduces levels of reactive oxygen species (ROS), accompanied by a decreased response to ROS-associated genotoxic agents (eg, ferroptosis inducer RSL3) and acquisition of an increasingly aggressive phenotype on serial transplantation in mice. Our single-cell cellular indexing of transcriptomes and epitopes by sequencing analysis on patient-derived LSCs in PDX mice and subsequent functional studies in murine LSCs and primary AML patient cells show that loss of GADD45A is associated with resistance to ferroptosis (an iron-dependent oxidative cell death caused by ROS accumulation) through aberrant activation of antioxidant pathways related to iron and ROS detoxification, such as FTH1 and PRDX1, upregulation of which correlates with unfavorable outcomes in patients with AML. These results reveal a therapy resistance mechanism contributing to poor prognosis and support a role for GADD45A loss as a critical step for leukemia-initiating activity and as a target to overcome resistance in aggressive leukemia.

Supplementary Figures 1-7 from Gadd45a Functions as a Promoter or Suppressor of Breast Cancer Dependent on the Oncogenic Stress

Gadd45a, Gadd45b, and Gadd45g have been implicated in cell cycle arrest, DNA repair, apoptosis, innate immunity, genomic stability, and modulation of normal blood cell development and leukemia. Each of the Gadd45 genes was shown to be regulated independently in myeloid cells in response to cytokine stimulation modulating blood cell survival and differentiation, including maintaining the quiescent stem cell pool. Gadd45a and Gadd45b were also shown to mediate the protective effects from UV in hematopoietic cells by separate signaling pathways involving either p38 activation or JNK inhibition. Furthermore, it was shown that gadd45a methylation in AML is predictive of poor survival. It was also shown that loss of Gadd45b accelerates the development of BCR-ABL driven CML in mice and leads to decreased median survival. The Gadd45b-deficient CML progenitors exhibited increased proliferation and decreased apoptosis, and this was associated with hyper-activation of c-Jun NH2-terminal kinase and Stat5. Moreover, loss of Gadd45a also accelerated the development of BCR-ABL driven CML, and this was associated with enhanced PI3K-AKT-mTOR-4E-BP1 signaling, upregulation of p30C/EBPα expression, and hyper-activation of p38 and Stat5. In human patients with chronic phase CML, gadd45a expression is up-regulated, whereas in accelerated and blast crisis phase patients, gadd45a is downregulated. Collectively, these results provide novel evidence that Gadd45a functions as a suppressor of BCR/ABL driven leukemia and may serve as a unique prognostic marker of CML progression. Thus Gadd45 proteins provide excellent targets for leukemia therapy.

Gadd45a, Gadd45b, and Gadd45g have been implicated in cell cycle arrest, DNA repair, apoptosis, innate immunity, genomic stability, and more recently in senescence. Evidence has accumulated that Gadd45a deficiency results in escape of mouse embryo fibroblasts from senescence, whereas Gadd45b deficiency promotes premature senescence and skin aging. Moreover, recently Gadd45b deficiency was found to promote senescence and attenuate liver fibrosis, whereas Gadd45a was observed to exert a protective effect against hepatic fibrosis. These findings indicate that the Gadd45 stress response proteins play important roles in modulating cellular responses to senescence. Thus, exploring how Gadd45 proteins modulate cellular senescence has the potential to provide new and innovative tools to treat cancer as well as liver disease.

While Ras/mitogen-activated protein kinase (MAPK) signaling is activated in most human cancers, attempts to target this pathway using kinase active site inhibitors have not typically led to durable, clinical benefit. To address this shortcoming, we sought to test the feasibility of an alternative targeting strategy, focused on the ERK2 substrate binding domains, D and DBP. We found that disabling the ERK2-DBP domain in mice caused baseline erythrocytosis. Consequently, we investigated the role of the ERK2-D and -DBP domains in disease, using a JAK2-dependent model of polycythemia vera (PV). Importantly, inactivation of the ERK2-DBP domain promoted the progression of disease from PV to myelofibrosis (MF), suggesting that the ERK2-DBP domain normally opposes progression. ERK2-DBP inactivation also prevented oncogenic JAK2 kinase (JAK2V617F) from promoting oncogene-induced senescence (OIS) in vitro. The ERK2-DBP mutation attenuated JAK2-mediated OIS by preventing the physical interaction of ERK2 with the transcription factor, Egr1. Because inactivation of the ERK2-DBP created a functional ERK2 kinase limited to binding substrates through its D-domain, these data suggested that the D-domain substrates were responsible for promoting oncogene-induced progenitor growth and tumor progression, and that pharmacologic targeting of the ERK2-D domain might attenuate cancer cell growth. Indeed, pharmacologic agents targeting the ERK2-D domain were effective in attenuating the growth of JAK2-dependent myeloproliferative neoplasm cell lines. Taken together, these data indicate that the ERK-D and -DBP domains can play distinct roles in the progression of neoplasms and that the D-domain has the potential to be potent therapeutic target in Ras/MAPK dependent cancers.

Signals driving aberrant self-renewal in the heterogeneous leukemia stem cell (LSC) pool determine aggressiveness of acute myeloid leukemia (AML). We report that a positive modulator of canonical WNT signaling pathway, RSPO-LGR4, upregulates key self-renewal genes and is essential for LSC self-renewal in a subset of AML. RSPO2/3 serve as stem cell growth factors to block differentiation and promote proliferation of primary AML patient blasts. RSPO receptor, LGR4, is epigenetically upregulated and works through cooperation with HOXA9, a poor prognostic predictor. Blocking the RSPO3-LGR4 interaction by clinical-grade anti-RSPO3 antibody (OMP-131R10/rosmantuzumab) impairs self-renewal and induces differentiation in AML patient-derived xenografts but does not affect normal hematopoietic stem cells, providing a therapeutic opportunity for HOXA9-dependent leukemia.

Evidence for reduced expression of cyclin G associated kinase (GAK) in glomeruli of patients with chronic kidney disease was observed in the Nephroseq human database, and GAK was found to be associated with the decline in kidney function. To examine the role of GAK, a protein that functions to uncoat clathrin during endocytosis, we generated podocyte-specific Gak-knockout mice (Gak-KO), which developed progressive proteinuria and kidney failure with global glomerulosclerosis. We isolated glomeruli from the mice carrying the mutation to perform messenger RNA profiling and unearthed evidence for dysregulated podocyte calpain protease activity as an important contributor to progressive podocyte damage. Treatment with calpain inhibitor III specifically inhibited calpain-1/-2 activities, mitigated the degree of proteinuria and glomerulosclerosis, and led to a striking increase in survival in the Gak-KO mice. Podocyte-specific deletion of Capns1, essential for calpain-1 and calpain-2 activities, also improved proteinuria and glomerulosclerosis in Gak-KO mice. Increased podocyte calpain activity–mediated proteolysis of IκBα resulted in increased NF-κB p65–induced expression of growth arrest and DNA-damage-inducible 45 beta in the Gak-KO mice. Our results suggest that loss of podocyte-associated Gak induces glomerular injury secondary to calcium dysregulation and aberrant calpain activation, which when inhibited, can provide a protective role.

Gadd45b is a member of Gadd45 stress sensor protein family that also includes Gadd45a & Gadd45g. To investigate the effect of Gadd45b in bcr-abl oncogene driven chronic myeloid leukemia (CML) development, syngeneic wild type lethally irradiated mice were reconstituted with either wild type or Gadd45b null myeloid progenitors transduced with a retroviral vector expressing BCR-ABL. Loss of Gadd45b was observed to accelerate BCR-ABL driven CML development with shortened median mouse survival time. BCR-ABL Gadd45b deficient CML progenitors exhibited increased proliferation and decreased apoptosis, associated with hyper-activation of c-Jun NH2-terminal kinase and Stat5. These results provide novel evidence that gadd45b, like gadd45a, functions as a suppressor of BCR-ABL driven leukemia, albeit via a different mechanism.

The Gadd45a stress sensor gene is a member in the Gadd45 family of genes that includes Gadd45b & Gadd45g. To investigate the effect of GADD45A in the development of CML, syngeneic wild type lethally irradiated mice were reconstituted with either wild type or Gadd45a null myeloid progenitors transduced with a retroviral vector expressing the 210-kD BCR-ABL fusion oncoprotein. Loss of Gadd45a was observed to accelerate BCR-ABL driven CML resulting in the development of a more aggressive disease, a significantly shortened median mice survival time, and increased BCR-ABL expressing leukemic stem/progenitor cells (GFP+Lin- cKit+Sca+). GADD45A deficient progenitors expressing BCR-ABL exhibited increased proliferation and decreased apoptosis relative to WT counterparts, which was associated with enhanced PI3K-AKT-mTOR-4E-BP1 signaling, upregulation of p30C/EBPa expression, and hyper-activation of p38 and Stat5. Furthermore, Gadd45a expression in samples obtained from CML patients was upregulated in more indolent chronic phase CML samples and down regulated in aggressive accelerated phase CML and blast crisis CML. These results provide novel evidence that Gadd45a functions as a suppressor of BCR/ABL driven leukemia and may provide a unique prognostic marker of CML progression.

There is substantial evidence that early growth response-1 (Egr1) gene, a zinc-finger transcription factor, behaves as a tumor suppressor in leukemia. This includes reports from this laboratory that constitutive Egr1 overrides leukemia conferred by deregulated c-Myc or E2F-1 in the M1 myeloid leukemic cell line by promoting differentiation. To investigate the effect of Egr1 on the initiation and progression of Chronic Myelogenous Leukemia (CML), lethally irradiated syngeneic wild type mice were reconstituted with bone marrow (BM) from either wild type or Egr1 null mice transduced with a 210-kD BCR-ABL-expressing MSCV-retrovirus (bone marrow transplantation {BMT}). Loss of Egr1 was observed to accelerate the development of BCR-ABL driven leukemia in recipient mice, resulting in the development of a more aggressive disease, a significantly shortened median survival time, and increased BCR-ABL expressing leukemic stem/progenitor cells (GFP+Lin-cKit+Sca+). Egr1 deficient progenitors expressing BCR-ABL exhibited decreased apoptosis, and increased cell viability and proliferation relative to WT counterparts. Secondary BMT of BCR-ABL BM revealed that loss of Egr1 resulted in enrichment of LSCs, consistent with shorter survival time and more aggressive disease of these mice compared to WT counterparts. Furthermore, serial re-plating colony assays indicated that loss of Egr1 increased self-renewal ability of BCR-ABL expressing BM. These novel findings on the tumor suppressor role of Egr1 in CML provide the impetus to study the effect of altering Egr1 expression in AML, where the overall five year survival rate remains low. The effect of loss of Egr1 in CML could reflect its established functions in normal hematopoiesis, maintaining quiescence of HSCs and driving terminal differentiation to the monocyte/macrophage lineage. Gain of function studies should validate these conclusions and provide further rationale for increased Egr1 as a therapeutic target in AML.

ObjectiveThis study was aimed to evaluate whether maternal dried blood spots could be a potential source for the noninvasive fetal RHD genotyping, serving as a combined one-step test for both the First Trimester Screen and the fetal RHD genotyping.MethodBoth the maternal dried blood spots and the peripheral blood samples from 19 RhD-negative pregnant women were obtained during the First Trimester Screen. DNA was extracted and sequential real-time PCRs were performed to determine the fetal RHD genotypes. Fetal RhD serological types were obtained after delivery. This study was approved by the Institutional Review Board, and informed consents were obtained.ResultsA total of 19/19 fetal RHD genotyping with maternal DBS were consistent with the follow-up serological RhD test results after birth. Eleven were RhD positive, and eight were RhD negative (RHD deletion or RHD-CE-D=6, RHD pseudogene=1, RHDVI=1). Sensitivity=100%, specificity=100%, positive predictive value=100%, negative predictive value=100%. A total of 18/19 fetal gender were determined correctly with maternal DBS. One female fetus was falsely determined as male. Sensitivity=100%, specificity=91.6%, positive predictive value=87.5%, negative predictive value=100%.ConclusionMaternal dried blood spots, with the benefits of flexible sample transportation and processing, could be utilized for the noninvasive prenatal fetal RHD genotyping and potentially be incorporated into the routine First Trimester Screen. Larger scale study is in progress to implement fetal RHD genotyping in routine prenatal care. (c) 2017 John Wiley & Sons, Ltd.

The GADD45 family of proteins functions as stress sensors in response to various physiological and environmental stressors. Here we show that primary mouse embryo fibroblasts (MEFs) from Gadd45b null mice proliferate slowly, accumulate increased levels of DNA damage, and senesce prematurely. The impaired proliferation and increased senescence in Gadd45b null MEFs is partially reversed by culturing at physiological oxygen levels, indicating that Gadd45b deficiency leads to decreased ability to cope with oxidative stress. Interestingly, Gadd45b null MEFs arrest at the G2/M phase of cell cycle, in contrast to other senescent MEFs, which arrest at G1. FACS analysis of phospho-histone H3 staining showed that Gadd45b null MEFs are arrested in G2 phase rather than M phase. H2O2 and UV irradiation, known to increase oxidative stress, also triggered increased senescence in Gadd45b null MEFs compared to wild type MEFs. In vivo evidence for increased senescence in Gadd45b null mice includes the observation that embryos from Gadd45b null mice exhibit increased senescence staining compared to wild type embryos. Furthermore, it is shown that Gadd45b deficiency promotes senescence and aging phenotypes in mouse skin. Together, these results highlight a novel role for Gadd45b in stress-induced senescence and in tissue aging.

The transcription factor early growth response 1 (Egr-1) gene was identified as a macrophage differentiation primary response gene, shown to be essential for and to restrict differentiation along the macrophage lineage. There’s evidence consistent with Egr-1 behaving as a tumor suppressor of leukemia, both in vivo and in vitro, including (1) loss of Egr-1 associated with therapy derived MDS and AML; (2) deregulated Egr-1 overriding blocks in myeloid differentiation, and (3) haplo-insufficiency of Egr-1 in mice leading to increased development of myeloid disorders following treatment with the potent DNA alkylating agent, N- ethyl-nitrosourea (ENU). BCR-ABL driven leukemia (Chronic Myelogenous Leukemia [CML]) was chosen as a model system to investigate the role of Egr-1 as a tumor suppressor for leukemia. CML is a disease resulting from the neoplastic transformation of hematopoietic stem cells (HSC) with the BCR-ABL oncogene. To assess the effect of Egr-1 on BCR-ABL driven leukemia, lethally irradiated syngeneic wild type mice were reconstituted with bone marrow (BM) from either wild type or Egr-1 null mice transduced with a 210-kD BCR-ABL-expressing MSCV-GFP retrovirus (bone marrow transplantation {BMT}). It was observed that loss of Egr-1 accelerated the development of BCR-ABL driven leukemia in recipient mice. Analysis of hematopoietic organs is consistent with loss of Egr-1 accelerating development of CML but not altering the nature of the disease. Cells expressing BCR-ABL that are null for Egr-1 exhibit increased survival and proliferation, which can account for some of the above observations. Substantial evidence is available that loss of Egr1 increases the leukemia initiating cell population, which can account for the more rapid development of disease. An increased population of lineage negative BM cells was observed in Egr-1-/- BCR-ABL recipient mice compared to animals transplanted with WT BCR-ABL BM. Serial BMT has shown that Egr-1-/- BCR-ABL BM has an increased leukemic burden compared to the WT counterpart. Furthermore, data from serial colony transfer experiments confirmed that loss of Egr-1 increases leukemia initiating cells. Preliminary studies on the effect of gain of Egr-1 function are consistent with the tumor suppressor behavior of Egr-1. These data as well as analysis of human CML samples will be presented. Further investigation could result in novel targets for diagnosis, prognosis, and targeted therapeutics, including strategies for activating Egr-1 expression that can be used to treat CML, as well as other leukemic diseases. Disclosures No relevant conflicts of interest to declare.

The BCR-ABL fusion oncogene which encodes a fused deregulated tyrosine kinase causes chronic myelogenous leukemia (CML) in humans. Imatinib, a small molecule ABL kinase inhibitor has been highly effective in treating chronic phase (CP) CML patients. However, a substantial number of patients undergo relapse due to development of resistance to imatinib therapy that leads to blast crisis (BC-CML), which is invariably fatal within weeks to months. Additional genetic aberrations assist in progression and identification of key players that are responsible for transformation is of utmost importance from a therapeutic point of view. Growth arrest DNA damage 45a (Gadd45a) gene, a member in the gadd45 family of genes including Gadd45b & Gadd45g, was identified as a myeloid differentiation primary response gene. There is evidence consistent with it’s involvement in G2/M cell cycle arrest and apoptosis in response to multiple stressors, including genotoxic and oncogenic stress. To investigate the effect of Gadd45a in the development of CML, adaptive bone marrow transplantation experiments with either wild type or Gadd45a null myeloid progenitors expressing 210-kD BCR-ABL fusion oncoprotein revealed that loss of Gadd45a accelerated BCR-ABL driven CML resulting in the development of a more aggressive AML/BC like disease. Recent newly obtained data indicate that number of Gadd45a deficient Leukemic stem cells (LSC) harboring BCR-ABL increased as disease progressed confirming Gadd45a as a crucial tumor suppressor in CML. Recent data also indicate, that transformed Gadd45a deficient progenitors exhibit increased proliferation and decreased apoptosis, associated with enhanced PI3K-AKT-mTOR-4E-BP1 signaling and upregulated oncogenic p30C/EBPα. More importantly, newly obtained data indicate that Gadd45a transcript levels in peripheral blood of human blast crisis (BC-CML) samples was found to be reduced compared to accelerated phase (AP-CML), chronic phase (CP-CML) and normal controls, assessed by Quantitative real time PCR analysis. Collectivly these data strongly suggest that Gadd45a expression is a novel prognostic indicator of CML progression, implicating Gadd45a as a downregulated target of BCR-ABL associated with progression to more aggressive stages. To conclude, our findings provide novel evidence that Gadd45a functions as a suppressor of BCR/ABL driven myeloid leukemogenesis, & that suppresion of Gadd45a is associated with CML progression. These data provide the impetus to further elucidate the role Gadd45a plays in suppressing the development of CML, and explore how its loss contributes to the progression of CML to more aggressive leukemic phenotypes. Disclosures: No relevant conflicts of interest to declare.

Abstract Gadd45a, Gadd45b, and Gadd45g encode for small (18 kD), evolutionarily conserved proteins that play a pivotal role in diverse cellular functions such as cell cycle arrest, DNA repair, and are regulated by the nature of the stress stimulus encountered, its magnitude, and the cell type. Here, we show that Gadd45b negatively regulates stress-induced senescence. By using the 3T3 growth protocol to study tissue culture-induced senescence; we observed that Gadd45b KO MEFs display reduced growth rates at early passages (by passage 5) compared to wild type (WT) MEFs. Notably, this is in contrast with Gadd45a KO MEFs that show enhanced growth rate and escape senescence. Furthermore, senescence associated (SA) βgal staining showed increased blue stained cells at earlier passages in Gadd45b KO MEFs compared to WT MEFs. When MEFs were cultured at 3% oxygen, Gadd45b KO MEFs at 3% oxygen showed increased growth rate compared to MEFs at 21% oxygen, but growth was still retarded compared to WT MEFs at 21%, indicating that Gadd45b KO MEFs have increased sensitivity to oxidative stress leading to increased senescence. Additionally, we also observed that Gadd45b levels in WT MEFs increased with increasing passage number. Propidium Iodide staining and FACS analysis showed that Gadd45b KO MEFs arrest at the G2M phase of cell cycle. At passage 7, the majority (75%) of Gadd45b KO MEFs were observed to arrest at the G2M phase, whereas only 15% of WT MEFs arrested at G2M. This finding is in striking contrast to other senescent MEFs, which normally arrest at G1. Furthermore, FACS analysis of phospho-histone H3 (ser10) stained cells (mitotic) showed that, Gadd45b KO MEFs have less phospho-histone H3-positive cells than WT MEFs indicating that Gadd45b KO MEFs are arrested in G2 phase rather than M phase. Recent data also indicate that Gadd45b KO MEFs show increased phospho-histone H2Ax and phospho-p53 staining compared to WT MEFs, suggesting that loss of Gadd45b leads to increased DNA damage signaling. Interestingly, other stressors such as sub-lethal H2O2 as well as UV irradiation, known to increase oxidative stress, were observed to trigger increased premature senescence in Gadd45b KO MEFs compared to WT MEFs. Notably, staining embryos for SA βgal, we show that embryos from Gadd45b KO mice exhibit increased SA βgal staining compared to WT embryos, thus providing in vivo evidence for increased senescence in Gadd45b KO mice. Taken together, these data provide the impetus to further elucidate the role of Gadd45b in G2 arrest and premature senescence. Note: This abstract was not presented at the meeting. Citation Format: Andrew Magimaidas, Barbara Hoffman, Dan Liebermann. Gadd45b deficiency impairs G2/M cell cycle progression leading to premature senescence. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2252. doi:10.1158/1538-7445.AM2014-2252

Background Gadd45a is a member of the Gadd45 family of genes that are known stress sensors. Gadd45a has been shown to serve as an effector in oncogenic stress in breast carcinogenesis in murine models. The present study was aimed at clarifying the expression of Gadd45a in human breast cancer and its correlation with clinicopathologic features. Methods The expression levels of Gadd45a in breast tissue samples of female breast surgery cases were examined by immunohistochemistry (IHC) using a Gadd45a antibody. Percent staining was determined and statistical analyses were applied to determine prognostic correlations. Results 56 female breast surgery cases were studied: Normal (11), Luminal A (9), Luminal B (11), HER2+ (10), Triple Negative (15). There was a highly significant difference in percent Gadd45a staining between groups [Mean]: Normal 16.3%; Luminal A 65.3%; Luminal B 80.7%; HER2+ 40.5%; TN 32%, P < 0.001, ANOVA. Gadd45a IHC levels for Normal cases found 82% negative/low. Luminal A breast cancer cases were found to be 67% high. Luminal B breast cancers were 100% high. Her2+ cases were 50% negative/low. Triple Negative cases were 67% negative/low. This difference in distribution of Gadd45a levels across breast cancer receptor subtypes was significant, P = 0.0009. Conclusions Gadd45a levels are significantly associated with hormone receptor status in human breast cancer. Normal breast tissue displays low Gadd45a levels. High Gadd45a levels are associated with Luminal A and Luminal B subtypes. Absence of hormone receptors in Triple Negative subtype is associated with Negative/Low levels of Gadd45a. Further studies are indicated to elucidate the role of Gadd45a in breast cancer as a potential prognosticator or target for treatment.

Emerging evidence indicates that the Gadd45 family of genes play a unique and critical role as sensors of stress, including genotoxic, physiological and oncogenic stress. The stress response Gadd45 fa