Proximity proteomics reveals role of Abelson interactor 1 in the regulation of TAK1/RIPK1 signaling

Dysregulation of the adaptor protein Abelson interactor 1 (ABI1) is linked to malignant transformation. To interrogate the role of ABI1 in cancer development, we mapped the ABI1 interactome using proximity-dependent labeling (PDL) with biotin followed by mass spectrometry. Using a novel PDL data filtering strategy, considering both peptide spectral matches and peak areas of detected peptides, we identified 212 ABI1 proximal interactors. These included WAVE2 complex components such as CYFIP1, NCKAP1, or WASF1, confirming the known role of ABI1 in the regulation of actin-polymerization-dependent processes. We also identified proteins associated with the TAK1-IKK pathway, including TAK1, TAB2, and RIPK1, denoting a newly identified function of ABI1 in TAK1-NF-κB inflammatory signaling. Functional assays using TNFα-stimulated, ABI1-overexpressing or ABI1-deficient cells showed effects on the TAK1-NF-kB pathway-dependent signaling to RIPK1, with ABI1-knockout cells being less susceptible to TNFα-induced, RIPK1-mediated, TAK1-dependent apoptosis. In sum, our PDL-based strategy enabled mapping of the ABI1 proximal interactome, thus revealing a previously unknown role of this adaptor protein in TAK1/RIPK1-based regulation of cell death and survival.

NF-κB signaling in neoplastic transition from epithelial to mesenchymal phenotype

NF-κB transcription factors are critical regulators of innate and adaptive immunity and major mediators of inflammatory signaling. The NF-κB signaling is dysregulated in a significant number of cancers and drives malignant transformation through maintenance of constitutive pro-survival signaling and downregulation of apoptosis. Overactive NF-κB signaling results in overexpression of pro-inflammatory cytokines, chemokines and/or growth factors leading to accumulation of proliferative signals together with activation of innate and select adaptive immune cells. This state of chronic inflammation is now thought to be linked to induction of malignant transformation, angiogenesis, metastasis, subversion of adaptive immunity, and therapy resistance. Moreover, accumulating evidence indicates the involvement of NF-κB signaling in induction and maintenance of invasive phenotypes linked to epithelial to mesenchymal transition (EMT) and metastasis. In this review we summarize reported links of NF-κB signaling to sequential steps of transition from epithelial to mesenchymal phenotypes. Understanding the involvement of NF-κB in EMT regulation may contribute to formulating optimized therapeutic strategies in cancer. Video Abstract.

Transcriptomics of acute myeloid leukaemia core bone marrow biopsies reveals distinct therapy response-specific osteo-mesenchymal profiles

While the bone marrow (BM) microenvironment is significantly remodelled in acute myeloid leukaemia (AML), molecular insight into AML-specific alterations in the microenvironment has been historically limited by the analysis of liquid marrow aspirates rather than core biopsies that contain solid-phase BM stroma. We assessed the effect of anthracycline- and cytarabine-based induction chemotherapy on both haematopoietic and non-haematopoietic cells directly in core BM biopsies using RNA-seq and histological analysis. We compared matched human core BM biopsies at diagnosis and 2 weeks after cytarabine- and anthracycline-based induction therapy in responders (<5% blasts present after treatment) and non-responders (≥5% blasts present after treatment). Our data indicated enrichment in vimentin (VIM), platelet-derived growth factor receptor beta (PDGFRB) and Snail family transcriptional repressor 2 (SNAI2) transcripts in responders, consistent with the reactivation of the mesenchymal population in the BM stroma. Enrichment of osteoblast maturation-related transcripts of biglycan (BGN), osteopontin (SPP1) and osteonectin (SPARC) was observed in non-responders. To the best of our knowledge, this is the first report demonstrating distinct osteogenic and mesenchymal transcriptome profiles specific to AML response to induction chemotherapy assessed directly in core BM biopsies. Detailing treatment response-specific alterations in the BM stroma may inform optimised therapeutic strategies for AML.

Engraftment, Fate, and Function of HoxB8-Conditional Neutrophil Progenitors in the Unconditioned Murine Host

The development and use of murine myeloid progenitor cell lines that are conditionally immortalized through expression of HoxB8 has provided a valuable tool for studies of neutrophil biology. Recent work has extended the utility of HoxB8-conditional progenitors to the in vivo setting via their transplantation into irradiated mice. Here, we describe the isolation of HoxB8-conditional progenitor cell lines that are unique in their ability to engraft in the naïve host in the absence of conditioning of the hematopoietic niche. Our results indicate that HoxB8-conditional progenitors engraft in a β1 integrin-dependent manner and transiently generate donor-derived mature neutrophils. Furthermore, we show that neutrophils derived in vivo from transplanted HoxB8-conditional progenitors are mobilized to the periphery and recruited to sites of inflammation in a manner that depends on the C-X-C chemokine receptor 2 and β2 integrins, the same mechanisms that have been described for recruitment of endogenous primary neutrophils. Together, our studies advance the understanding of HoxB8-conditional neutrophil progenitors and describe an innovative tool that, by virtue of its ability to engraft in the naïve host, will facilitate mechanistic in vivo experimentation on neutrophils.

Murine Leukemia-Derived Extracellular Vesicles Elicit Antitumor Immune Response

Background

Extracellular vesicles (EVs) are heterogeneous lipid bilayer particles secreted by cells. EVs contain proteins, RNA, DNA and other cargo that can have immunomodulatory effects. Cancer-derived EVs have been described as having immunomodulating effects in vivo with immunosuppressive and pro-tumor growth capabilities. However, cancer-derived EVs have also been harnessed and utilized for anti-cancer potential.

Methods

To assess the immunomodulatory effect of EVs produced by acute myeloid leukemia (AML) cells, we isolated vesicles secreted by the murine AML cell line, C1498, and investigated their effect on in vitro and in vivo immune responses.

Results

These leukemia-derived EVs were found to induce increased proliferation of CD3+ cells and enhanced cytolytic activity of CD3+ cells directed toward leukemic cells in vitro. Injection of leukemia-derived EVs into syngeneic naïve mice induced T cell responses in vivo and resulted in enhanced immune responses upon T cell re-stimulation in vitro.

Conclusion

These findings indicate that C1498-derived EVs have immunomodulatory effects on cell-mediated immune responses that could potentially be utilized to facilitate anti-leukemia immune responses.

Abstract PO-27: Clonotypic cell-free DNA (cfDNA) in the cerebrospinal fluid (CSF) of patients with aggressive lymphomas

Current methods for detection of CNS involvement in lymphoma (CSF cytology, flow cytometry) have very limited sensitivity, particularly in cases of parenchymal brain involvement. Early detection is critical to institute CNS-directed therapy and avert dismal outcomes of overt CNS recurrence. Clonotype-specific cfDNA can be detected in the plasma of patients with lymphoma using next-generation sequencing (NGS), and cfDNA-based minimal residual disease (MRD) assay can predict impending recurrence (Roschewski, Lancet Oncol 2015). cfDNA has not been systematically evaluated in the CSF, yet it may hold promise as a sensitive and specific method to detect CNS invasion. To evaluate the ability of an NGS-MRD assay in CSF to detect CNS invasion, we examined CSF and plasma samples from patients with aggressive lymphomas who either had overt CNS disease or who were without known CNS invasion, but at high clinical risk. Genomic DNA from primary tumors was analyzed for tumor-specific clonotype using NGS of rearranged IGK, IGH (VJ or DJ), or IGL loci (Adaptive Biotechnologies; Carlson, Nat Commun 2013). Tumor-specific clonotypes from each case were selected for subsequent tracking by NGS-MRD in CSF and plasma samples. Clonotype copy numbers are expressed per mL for acellular CSF, and clonotype frequency per all B cells. NGS identified median 3 (range, 2-7) dominant immunoglobulin sequences in each primary lymphoma (N=16), with median dominant clonotype frequency 50.3% (range, 26.8-9.28%). In the CSF, the NGS-MRD assay detected the dominant clonotype in 9 out of 16 samples, including all (N=4) with overt CNS invasion (sensitivity=100%), of which 2 had parenchymal disease only with negative CSF cytology, flow cytometry, or IGH PCR. Median detectable cfDNA clonotype in the CSF was 1,077 copies per mL (range, 2-5,620), with median clonotype frequency of 28.4% (range, 0.1-98.5%). cfDNA copy counts were significantly higher in cases with positive CSF cytology than those with parenchymal or clinically occult disease (P=.0016). We observed no significant correlation between the red blood cell count in the CSF and the cfDNA clonotype concentration (P=0.73) or frequency (P=0.62), suggesting that the presence of cfDNA in the CSF was not due to contamination by blood plasma. There was also no evident correlation between cfDNA in plasma and CSF. Within median 11 months of follow-up, 1 of 4 patients (25%) with a positive CSF NGS-MRD assay and no CNS disease developed a fatal CNS recurrence. Our results suggest that NGS-MRD assay for cfDNA in the CSF can identify intraparenchymal or leptomeningeal CNS invasion with high sensitivity, including cases not identifiable by traditional methods. Prognostic significance of detecting lymphoma-specific cfDNA in the CSF of high-risk patients without overt CNS disease will be explored in a larger sample. Pretreatment NGS-MRD assay could be prospectively tested to predict the risk of CNS recurrence and potentially enable more accurate selection of patients for CNS prophylaxis therapy.

Citation Format: Adam J. Olszewski, Anna Chorzalska, Habibe Kurt, Thomas A. Ollila, Diana O. Treaba, Andrew Hsu, Adam Zayac, John L. Reagan, Ilyas Sahin, William Rafelson, Pamela C. Egan, Jordan Robison, John Vatkevich, Chelsea D. Mullins, Max Petersen, Patrycja M. Dubielecka. Clonotypic cell-free DNA (cfDNA) in the cerebrospinal fluid (CSF) of patients with aggressive lymphomas [abstract]. In: Proceedings of the AACR Virtual Meeting: Advances in Malignant Lymphoma; 2020 Aug 17-19. Philadelphia (PA): AACR; Blood Cancer Discov 2020;1(3_Suppl):Abstract nr PO-27.

Overexpression of Tpl2 is linked to imatinib resistance and activation of MEK-ERK and NF-κB pathways in a model of chronic myeloid leukemia

The introduction of tyrosine kinase inhibitors (TKI) has transformed chronic myeloid leukemia (CML) into a chronic disease with long-term survival exceeding 85%. However, resistance of CML stem cells to TKI may contribute to the 50% relapse rate observed after TKI discontinuation in molecular remission. We previously described a model of resistance to imatinib mesylate (IM), in which K562 cells cultured in high concentrations of imatinib mesylate showed reduced Bcr-Abl1 protein and activity levels while maintaining proliferative potential. Using quantitative phosphoproteomic analysis of these IM-resistant cells, we have now identified significant upregulation of tumor progression locus (Tpl2), also known as cancer Osaka thyroid (COT1) kinase or Map3k8. Overexpression of Tpl2 in IM-resistant cells was accompanied by elevated activities of Src family kinases (SFKs) and NF-κB, MEK-ERK signaling. CD34+ cells isolated from the bone marrow of patients with CML and exposed to IMin vitro showed increased MAP3K8 transcript levels. Dasatinib (SFK inhibitor), U0126 (MEK inhibitor), and PS-1145 (IκB kinase (IKK) inhibitor) used in combination resulted in elimination of 65% of IM-resistant cells and reduction in the colony-forming capacity of CML CD34+ cells in methylcellulose assays by 80%. In addition, CML CD34+ cells cultured with the combination of inhibitors showed reduced MAP3K8 transcript levels. Overall, our data indicate that elevated Tpl2 protein and transcript levels are associated with resistance to IM and that combined inhibition of SFK, MEK, and NF-κB signaling attenuates the survival of IM-resistant CML cells and CML CD34+ cells. Therefore, combination of SFK, MEK, and NF-κB inhibitors may offer a new therapeutic approach to overcome TKI resistance in CML patients.

Long-Term Exposure to Imatinib Mesylate Downregulates Hippo Pathway and Activates YAP in a Model of Chronic Myelogenous Leukemia

Despite the success of tyrosine kinase inhibitor (TKI) therapy in chronic myelogenous leukemia (CML), leukemic stem/progenitor cells remain detectable even in the state of deep molecular remission. Mechanisms that allow them to persist despite continued kinase inhibition remain unclear. We have previously shown that prolonged exposure to imatinib mesylate (IM) results in dysregulation of Akt/Erk 1/2 signaling, upregulation of miR-181a, enhanced adhesiveness, and resistance to high IM. To characterize the molecular basis and reversibility of those effects, we applied gene and protein expression analysis, quantitative phosphoproteomics, and direct miR-181a inhibition to our cellular model of CML cells subjected to prolonged exposure to IM. Those cells demonstrated upregulation of pluripotency markers (SOX2, SALL4) and adhesion receptors (CD44, VLA-4, CXCR4), as well as downregulation of Hippo signaling and upregulation of transcription coactivator YAP. Furthermore, inhibition of miR-181a using a microRNA sponge inhibitor resulted in decreased transcription of SOX2 and SALL4, decreased activation of YAP, and increased sensitivity to IM. Our findings indicate that long-term exposure to IM results in dysregulation of stem cell renewal-regulatory Hippo/YAP signaling, acquisition of expression of stem cell markers and that experimental interference with YAP activity may help to restore chemosensitivity to TKI.

PKC-θ is a negative regulator of TRAIL-induced and FADD-mediated apoptotic spectrin aggregation

INTRODUCTION

During studies on chemotherapy-induced apoptosis in lymphoid cells, we noted that aggregation of spectrin occurred early in apoptosis, i.e. before activation of initiator caspase(s) and prior to exposure of phosphatidylserine (PS). We also found that protein kinase C theta (PKC-θ) co-localized with spectrin in these aggregates. Our previously published studies indicated that in formation of early apoptotic spectrin aggregates, either PKC-θ or other apoptosis-related proteins are involved. Taking into consideration above data, we decided to test the effect of PKC-θ and Fas-associated death domain protein (FADD) on spectrin aggregation in these cells during tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis.

MATERIAL AND METHODS

For PKC-θ gene (PRKCQ) or FADD gene expression silencing in Jurkat T cells we used lentiviral particles containing shRNA and scrambled shRNA, respectively. Spectrin aggregates were detected by Western blotting after Triton-X 100 extraction in pellet and soluble fractions or by confocal imaging.

RESULTS

TRAIL-induced apoptosis results in spectrin aggregation and leads to translocation and aggregation of PKC-θ. We found that phorbol-myristate acetate, a PKC activator and translocation inducer, has only a small effect on spectrin aggregation. To further confirm this, we have also shown that knock down ofPRKCQin Jurkat T cells accelerates the formation of TRAIL-induced spectrin aggregates. Transient overexpression of theβ-spectrin C-terminal fragment, containing multiple S/T phosphorylation sites, potential substrate sites for PKC-θ, accelerated the formation of spectrin aggregates. Silencing of downstream TRAIL receptor effector gene,FADD, delayed aggregation of spectrin, but did not reduce PKC-θ localization to the plasma membrane.

CONCLUSIONS

In summary, our results show for the first time involvement of spectrin aggregation in TRAIL receptor-FADD apoptotic pathway and indicate that TRAIL-induced spectrin aggregate formation is mediated by FADD and negatively regulated by PKC-θ.

Abstract B08: New Abelson interactor-1(Abi-1)-driven mechanism of acquired drug resistance

In hematological malignancies, quiescent leukemic stem cells are responsible for persistence of minimal residual disease and relapse. We have recently identified a new signaling pathway that is significantly dysregulated in imatinib mesylate (IM) resistant leukemic cells (Chorzalska et all, Leukemia in press). A key player in this pathway is Abelson interactor-1 (Abi-1). Abi-1 was originally identified as Abl kinase associating protein that was later confirmed to be one of the Bcr-Abl interactors. Abi-1 was recently shown to interact directly with α4 integrin, which controls lodging of hematopoietic and leukemic stem cells (HSCs/LSCs) in the bone marrow microenvironment. We have recently obtained evidence that Abi-1 plays a role in signaling cross-talk between Bcr-Abl and α4 integrin. We have found that loss of Abi-1 leads to increased adhesion and quiescence, resulting in increased chemoresistance of leukemic CD34+ progenitor cells. Comparison of Abi-1 (ABI-1) and α4 integrin (ITGA4) gene expression in relapsing Bcr-Abl positive CD34+ progenitor cells demonstrated a reduction in Abi-1 and an increase in α4 integrin mRNA in the absence of Bcr-Abl mutations. This inverse correlation between Abi-1 and α4 integrin expression, as well as linkage to elevated phospho-Akt and phospho-Erk signaling, was confirmed in imatinib mesylate (IM) resistant leukemic cells. These results indicate that the α4-Abi-1 signaling pathway may mediate acquisition of the drug resistant phenotype of leukemic cells. Based on our findings, we hypothesize that chemoresistance arises as a consequence of dysregulation of a pathway involving α4 integrin and Abi-1, and is mediated through a previously unknown mechanism that is independent of oncogene activity.

Citation Format: Anna Chorzalska, Ibrahem Salloum, Philip Marjon, Diana Treaba, Christoph Schorl, Morgan John, Christine R. Bryke, John Reagan, Eric Winer, Adam J. Olszewski, Patrycja M. Dubielecka. New Abelson interactor-1(Abi-1)-driven mechanism of acquired drug resistance. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Drug Sensitivity and Resistance: Improving Cancer Therapy; Jun 18-21, 2014; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(4 Suppl): Abstract nr B08.

Abstract B06: Abi1 levels regulate prostate tumor progression in mice downstream from Pten inactivation

With over 200,000 new cases and nearly 30,000 deaths every year, prostate cancer remains one of the most critical healthcare issues in the United States. Prostate cancer is progressive, eventually leading to an aggressive and metastatic disease. Although indolent disease can be left untreated (watchful waiting or symptomatically treated), predicting which tumors will progress to the metastatic and lethal stage of the disease is problematic. More comprehensive knowledge of disease-progression mechanisms in prostate cancer treatment decisions would offer considerable saving to society in treatment costs and effort, and would likely improve patient quality of life by reducing the number of patients treated with radical therapies.

Mouse models recapitulate well many stages of human pathology associated with prostate tumor progression. Tumor invasiveness involves dysregulation of actin cytoskeleton. Abi1 is the key component of actin polymerization regulatory WAVE complex. WAVE complex plays important role in a variety of cellular processes, including protrusion formation during cell migration and the formation of adherens junctions, indicating the critical importance of Abi1 for cell-to-cell adhesion and cell motility. ABI1 is implicated in variety of human cancers including initiation of prostate cancer (Oncogenesis. 2012; 1:e26) but its role in tumor progression is unknown.

In a search for molecular mechanism of tumor progression here we modeled the effect of ABI1 inactivation in absence of PTEN gene, which is the most commonly mutated gene in human prostate cancer. Prostate specific inactivation of Pten and Abi1 genes in mice led to establishment of progression-specific prostate tumorigenesis models in mice. Preliminary data indicate that Abi1 controls tumor invasiveness resulting from Pten loss in a dose dependent manner. By modifying Abi1 and Pten gene dose using the double Abi1/Pten KO mouse, three models of prostate cancer progression were produced: Model 1, a model of invasive carcinoma (complete Pten and Abi1 loss, mice with the genotype: [Abi1(fl/fl); Pten(fl/fl); PbCre+]); Model 2, a model of changes consistent with high grade PIN with partial progression to invasive carcinoma (complete Pten loss, single copy of Abi1 present, mice with the genotype: [Abi1(wt/fl); Pten(fl/fl); PbCre+]); and, Model 3, a model of noninvasive prostate cancer with development of changes similar to low grade PIN (complete Abi1 loss, single copy of Pten present, mice with the genotype: [Abi1(fl/fl); Pten(wt/fl); PbCre+]). Histopathological changes observed in Abi1/Pten double KO are being compared to Pten KO alone to evaluate the influence of Abi1 on dynamics of tumor progression due to Pten loss.

Analysis of Abi1/Pten double KO mice indicates that activation of PI-3 kinase activity is coincident with abnormal regulation of actin cytoskeleton. Examination of molecular and biochemical changes indicate that Pten inactivation alone resulted in up-regulation of Abi1 levels. Hence, Abi1 inactivation-mediated abrogation of oncogenic effects due to Pten loss in the double Abi1/Pten KO mouse is consistent with Abi1's tumor suppressor function. We propose that Abi1 levels control tumor progression by controlling level of actin dysregulation associated with tumor invasion. As Abi1/WAVE complex and Pten dysregulation are observed in human pathology it is hoped that the analysis of Abi1/Pten KO mouse model will lead to better understanding of tumor progression in human prostate cancer and to translation of the findings from bench to bedside.

Citation Format: Anna Chorzalska, Xiaoling Xiong, Andrea Lunardi, Julie R. White, Janet A. Sawicki, Gennady Bratslavsky, Pier Paolo Pandolfi, Leszek Kotula. Abi1 levels regulate prostate tumor progression in mice downstream from Pten inactivation. [abstract]. In: Proceedings of the AACR Special Conference: The Translational Impact of Model Organisms in Cancer; Nov 5-8, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(11 Suppl):Abstract nr B06.

Low expression of Abelson interactor-1 is linked to acquired drug resistance in Bcr-Abl-induced leukemia

The basis for persistence of leukemic stem cells in the bone marrow microenvironment (BMME) remains poorly understood. We present evidence that signaling crosstalk between α4 integrin and Abelson interactor-1 (Abi-1) is involved in acquisition of an anchorage-dependent phenotype and drug resistance in Bcr-Abl positive leukemia cells. Comparison of Abi-1 (ABI-1) and α4 integrin (ITGA4) gene expression in relapsing Bcr-Abl positive CD34+ progenitor cells demonstrated a reduction in Abi-1 and an increase in α4 integrin mRNA in the absence of Bcr-Abl mutations. This inverse correlation between Abi-1 and α4 integrin expression, as well as linkage to elevated phospho-Akt and phospho-Erk signaling, was confirmed in imatinib mesylate (IM) resistant leukemic cells. These results indicate that the α4-Abi-1 signaling pathway may mediate acquisition of the drug resistant phenotype of leukemic cells.

Disruption of Abi1/Hssh3bp1 expression induces prostatic intraepithelial neoplasia in the conditional Abi1/Hssh3bp1 KO mice

Prostate cancer is one of the leading causes of cancer-related deaths in the United States and a leading diagnosed non-skin cancer in American men. Genetic mutations underlying prostate tumorigenesis include alterations of tumor suppressor genes. We tested the tumor suppressor hypothesis for ABI1/hSSH3BP1 by searching for gene mutations in primary prostate tumors from patients, and by analyzing the consequences of prostate-specific disruption of the mouse Abi1/Hssh3bp1 ortholog. We sequenced the ABI1/hSSH3BP1 gene and identified recurring mutations in 6 out of 35 prostate tumors. Moreover, complementation and anchorage-independent growth, proliferation, cellular adhesion and xenograft assays using the LNCaP cell line, which contains a loss-of-function Abi1 mutation, and a stably expressed wild-type or mutated ABI gene, were consistent with the tumor suppressor hypothesis. To test the hypothesis further, we disrupted the gene in the mouse prostate by breeding the Abi1 floxed strain with the probasin promoter-driven Cre recombinase strain. Histopathological evaluation of mice indicated development of prostatic intraepithelial neoplasia (PIN) in Abi1/Hssh3bp1 knockout mouse as early as the eighth month, but no progression beyond PIN was observed in mice as old as 12 months. Observed decreased levels of E-cadherin, β-catenin and WAVE2 in mouse prostate suggest abnormal cellular adhesion as the mechanism underlying PIN development owing to Abi1 disruption. Analysis of syngeneic cell lines point to the possibility that upregulation of phospho-Akt underlies the enhanced cellular proliferation phenotype of cells lacking Abi1. This study provides proof-of-concept for the hypothesis that Abi1 downregulation has a role in the development of prostate cancer.

Abstract A51: Disruption of Abi1/Hssh3bp1 expression induces prostatic intraepithelial neoplasia in the conditional Abi1/Hssh3bp1 KO mice

Prostate cancer is one of the leading causes of cancer-related deaths in the United States and a leading diagnosed non-skin cancer in American men. Genetic mutations underlying prostate cancer tumorigenesis include alterations of tumor suppressor genes. We previously proposed that ABI1/hSSH3BP1 acts as a tumor suppressor gene (Macoska, et al. 2001 Neoplasia 3, 99-104). Here, we tested this hypothesis by searching for ABI1 gene mutations in primary prostate tumors from patients, and by analyzing the consequences of prostate-specific disruption of the mouse Abi1/Hssh3bp1 orthologue. We sequenced the ABI1/hSSH3BP1 gene and identified mutations in 15 out of 44 prostate tumors. Moreover, complementation growth-, proliferation- and xenograft- assays using the LNCaP cell line, which contains the loss-of-function Abi1 mutation, and stably expressed wt ABI gene, were consistent with the tumor suppressor hypothesis. To test the hypothesis further, we disrupted the gene in the mouse prostate by breeding the Abi1 floxed strain with the probasin promoter-driven Cre recombinase strain. Histopathological evaluation of mice indicated development of prostatic intraepithelial neoplasia (PIN) in Abi1/Hssh3bp1 KO mouse as early as the 8th month, but no progression beyond PIN was observed in mice as old as 12 months. Observed decreased levels of E-cadherin, β-catenin, and WAVE2 in mouse prostate suggest abnormal cellular adhesion as the mechanism underlying PIN development due to Abi1 disruption. In summary, this study provides further evidence for the hypothesis that Abi1 down-regulation plays a role in the development of prostate cancer and warrants further investigations of Abi1's role in prostate cancer tumorigenesis.

Citation Format: Xiaoling Xiong, Leszek Kotula, Anna Chorzalska, Patrycja Dubielecka, Julie White, Yogindra Vedvyas, Cyrus V. Hedvat, Adriana Haimovitz-Friedman, Jason A. Koutcher, Janet A. Sawicki. Disruption of Abi1/Hssh3bp1 expression induces prostatic intraepithelial neoplasia in the conditional Abi1/Hssh3bp1 KO mice [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr A51.

Key amino acid residues of ankyrin-sensitive phosphatidylethanolamine/phosphatidylcholine-lipid binding site of βI-spectrin

It was shown previously that an ankyrin-sensitive, phosphatidylethanolamine/phosphatidylcholine (PE/PC) binding site maps to the N-terminal part of the ankyrin-binding domain of β-spectrin (ankBDn). Here we have identified the amino acid residues within this domain which are responsible for recognizing monolayers and bilayers composed of PE/PC mixtures. In vitro binding studies revealed that a quadruple mutant with substituted hydrophobic residues W1771, L1775, M1778 and W1779 not only failed to effectively bind PE/PC, but its residual PE/PC-binding activity was insensitive to inhibition with ankyrin. Structure prediction and analysis, supported by in vitro experiments, suggests that “opening” of the coiled-coil structure underlies the mechanism of this interaction. Experiments on red blood cells and HeLa cells supported the conclusions derived from the model and in vitro lipid-protein interaction results, and showed the potential physiological role of this binding. We postulate that direct interactions between spectrin ankBDn and PE-rich domains play an important role in stabilizing the structure of the spectrin-based membrane skeleton.

Expression, purification and functional characterization of recombinant human acyl-CoA-binding protein (ACBP) from erythroid cells

Fatty acyl-CoA esters are extremely important in cellular homeostasis. They are intermediates in both lipid metabolism and post-translational protein modifications. Among these modification events, protein palmitoylation seems to be unique by its reversibility which allows dynamic regulation of the protein hydrophobicity. The recent discovery of an enzyme family that catalyze protein palmitoylation has increased the understanding of the enzymology of the covalent attachment of fatty acids to proteins. Despite that, the molecular mechanism of supplying acyl-CoA esters to this reaction is yet to be established. Acyl-coenzyme A-binding proteins are known to bind long-chain acyl-CoA esters with very high affinity. Therefore, they play a significant role in intracellular acyl-CoA transport and pool formation. The purpose of this work is to explore the potential of one of the acyl-CoA-binding proteins to participate in the protein palmitoylation. In this study, a recombinant form of ACBP derived from human erythroid cells was expressed in E. coli, purified, and functionally characterized. We demonstrate that recombinant hACBP effectively binds palmitoyl-CoA in vitro, undergoing a shift from a monomeric to a dimeric state, and that this ligand-binding ability is involved in erythrocytic membrane phosphatidylcholine (PC) remodeling but not in protein acylation.

Expression, purification and functional characterization of recombinant human acyl-CoA-binding protein (ACBP) from erythroid cells

Fatty acyl-CoA esters are extremely important in cellular homeostasis. They are intermediates in both lipid metabolism and post-translational protein modifications. Among these modification events, protein palmitoylation seems to be unique by its reversibility which allows dynamic regulation of the protein hydrophobicity. The recent discovery of an enzyme family that catalyze protein palmitoylation has increased the understanding of the enzymology of the covalent attachment of fatty acids to proteins. Despite that, the molecular mechanism of supplying acyl-CoA esters to this reaction is yet to be established. Acyl-coenzyme A-binding proteins are known to bind long-chain acyl-CoA esters with very high affinity. Therefore, they play a significant role in intracellular acyl-CoA transport and pool formation. The purpose of this work is to explore the potential of one of the acyl-CoA-binding proteins to participate in the protein palmitoylation. In this study, a recombinant form of ACBP derived from human erythroid cells was expressed in E. coli, purified, and functionally characterized. We demonstrate that recombinant hACBP effectively binds palmitoyl-CoA in vitro, undergoing a shift from a monomeric to a dimeric state, and that this ligand-binding ability is involved in erythrocytic membrane phosphatidylcholine (PC) remodeling but not in protein acylation.

Fluorescence approach to evaluating conformational changes upon binding of beta-spectrin ankyrin-binding domain mutants with the lipid bilayer

The major component of the cell membrane skeleton, spectrin, is anchored in the cell membrane via interactions with membrane proteins. It has been previously shown that both erythroid and non-erythroid spectrin interact directly with membrane phospholipids (mainly aminophospholipids). One of the binding sites responsible for these interactions is located in the ankyrin-binding domain. In the present study, in order to better understand the character of binding, a more detailed investigation of the interactions between the beta-spectrin fragments corresponding to the truncated mutants of the ankyrin-binding domain (Frag1 and Frag3) and liposomes of different compositions were carried out. The obtained results suggest that the binding of both spectrin fragments with liposomes induces conformational changes within the protein. Analysis of the changes in intrinsic tryptophan fluorescence spectra upon binding with liposomes, together with quenching studies (from the water and membrane hydrocarbon environment), allows for qualitative description of changes in proteins conformation. Our results suggest that the largest conformational changes occur for Frag1 bound to PC : PE (2 : 3) liposomes what is consistent with previous studies on monolayers. They are also in good agreement with those obtained previously for native erythroid and nonerythroid spectrin molecules.

Mitoxantrone changes spectrin-aminophospholipid interactions

Understanding drug-membrane and drug-membrane protein interactions would be a crucial step towards understanding the action and biological properties of anthracyclines, as the cell membrane with its integral and peripheral proteins is the first barrier encountered by these drugs. In this paper, we briefly describe mitoxantrone-monolayer and mitoxantrone-bilayer interactions, focusing on the effect of mitoxantrone on the interactions between erythroid or nonerythroid spectrin with phosphatidylethanolamine-enriched mono- and bilayers. We found that mitoxantrone markedly modifies the interaction of erythroid and nonerythroid spectrins with phosphatidylethanolamine/phosphatidylcholine (PE/PC) monolayers. The change in delta pi induced by spectrins is several-fold larger in the presence of 72 nM mitoxantrone than in its absence: spectrin/mitoxantrone complexes induced a strong compression of the monolayer. Spin-labelling experiments showed that spectrin/mitoxantrone complexes caused significant changes in the order parameter measured using a 5'-doxyl stearate probe in the bilayer, but they practically did not affect the mobility of 16'-doxyl stearate. These results indicate close-to-surface interactions/penetrations without significant effect on the mid-region of the hydrophobic core of the bilayer. The obtained apparent equilibrium dissociation constants indicated relatively similar mitoxantrone-phospholipid and mitoxantrone-spectrin (erythroid and nonerythroid) binding affinities. These results might in part, explain the effect of mitoxantrone on spectrin distribution in the living cells.

The 22.5 kDa spectrin-binding domain of ankyrinR binds spectrin with high affinity and changes the spectrin distribution in cells in vivo

It was previously shown that ankyrins play a crucial role in the membrane skeleton arrangement. Purifying ankyrinR obtained from erythrocytes is a time-consuming process. Therefore, cloned and bacterially expressed ankyrinR-spectrin-binding domain (AnkSBD) is a demanded tool for studying spectrin-ankyrin interactions. In this communication, we report on the cloning and purification of AnkSBD and describe the results of binding experiments, in which we showed high-affinity interactions between the AnkSBD construct and isolated erythrocyte or non-erythroid spectrins. pEGFP-AnkSBD-transfected cells co-localised with non-erythroid spectrin in HeLa cells. The functional interactions of the AnkSBD construct in vivo and in vitro open many possibilities to study the structure and function of this domain, which has not yet been as extensively studied when compared to the aminoterminal domain of this protein.

Lipid-binding role of βII-spectrin ankyrin-binding domain

It is known that erythroid and non-erythroid spectrins binding of vesicles and monolayers containing PE proved sensitive to inhibition by red blood cell ankyrin. We now show that the bacterially-expressed recombinant peptides representing betaII(brain)-spectrin's ankyrin-binding domain and its truncated mutants showed lipid-binding activity, although only those containing a full-length amino terminal fragment showed high to moderate affinity towards phospholipid mono- and bilayers and a substantial sensitivity of this binding to inhibition by ankyrin. These results are in accordance with our published data on betaI-spectrin's ankyrin-binding domain [Hryniewicz-Jankowska A, et al. Mapping of ankyrin-sensitive, PE/PC mono- and bilayer binding site in erythroid beta-spectrin. Biochem J 2004;382:677-85]. Moreover, we tested also the effect of transient transfection of living cells of several cell-lines with vectors coding for GFP-conjugates including betaII and also betaI full-length ankyrin-binding domain and their truncated fragments on the membrane skeleton organization. The transfection with constructs encoding full-length ankyrin-binding domain of betaII and betaI spectrin resulted in increased aggregation of membrane skeleton and its punctate appearance in contrast to near normal appearance of membrane skeleton of cells transiently transfected with GFP control or construct encoding ankyrin-binding domain truncated at their N-terminal region. Our results therefore indicate the importance of N-terminal region for lipid-binding activity of the beta-spectrin ankyrin-binding domain and its substantial role in maintaining the spectrin-based skeleton distribution.

Spectrin-phospholipid interactions. Existence of multiple kinds of binding sites?

The object of this paper is to review briefly the studies on the interactions of erythroid and non-erythroid spectrins with lipids in model and natural membranes. An important progress on the identification of lipid-binding sites has recently been made although many questions remain still unanswered. In particular, our understanding of the physiological role of such interactions is still limited. Another important issue is the occurrence of spectrins in membrane rafts, how they are attached to the raft and what is their function in rafts.

Mapping of an ankyrin-sensitive, phosphatidylethanolamine/phosphatidylcholine mono- and bi-layer binding site in erythroid beta-spectrin

It has been shown previously that binding of vesicles and monolayers containing PE (phosphatidylethanolamine) by either erythroid or non-erythroid spectrin proved sensitive to inhibition by purified erythrocyte ankyrin. We tested the lipid-binding affinities of the purified ankyrin-binding domain of beta-spectrin and of its truncated mutants in four ways, by analysing: (1) penetration of 'loose' PE/PC (phosphatidylcholine) monolayers; (2) binding to liposomes in suspension; (3) competition with spectrin for liposomes; and (4) binding of a PE/PC monolayer in a surface plasmon resonance system. The results obtained indicated that the full-length ankyrin-binding domain bound PE/PC mono- and bi-layers with moderate affinity, penetrated monolayers and competed with spectrin for liposomes. Moreover, its truncated mutants that retained the N-terminal part, in contrast with those lacking eight or 38 N-terminal residues (which bound lipid mono- and bi-layers with lower affinity), bound PE/PC mono- and bi-layers with an affinity and capacity comparable with those of the full-length ankyrin-binding domain, and this activity was inhibited by purified erythrocyte ankyrin. The full-length domain, in contrast with the mutant lacking 38 N-terminal residues, induced a small increase in the fluidity of PE/PC membranes when probed with 5'-doxyl stearate, similar to the effect of purified spectrin. Therefore we conclude that the binding site for PE-rich lipids, which is sensitive to ankyrin inhibition, is located in a 38-residue N-terminal fragment of the beta-spectrin ankyrin-binding domain, and that the first eight residues play a key role in this activity.

The kinetics of haemolysis of spherocytic erythrocytes

Spherocytosis is a hereditary disease. It results from mutations in genes that encode proteins participating in the attachment of the membrane skeleton to the plasma membrane bilayer of the erythrocyte. In affected cells, interaction between the spectrin-actin meshwork and integral membrane proteins is altered. This results in the weakening of plasma membrane mechanical resistance and diminishing its elasticity. Since defective cells are prone to mechanical destruction and phagocytosis in the spleen, the fraction of morphologically-altered erythrocytes is rather small; this in turn means such an examination is prone to errors. In this paper, we describe a simple method which could be useful in the identification of red blood cells with altered osmotic properties. The method is based on the measurement of the amount of light scattered by a suspension of the red blood cells, during which cells are exposed to osmotic stress in the stopped-flow regime. The obtained plots are fitted to a mathematical formula, the parameters of which can be used as quantitative indicators of the changes in red blood cells' osmotic features. Two types of spherocytotic samples were examined: those with a proven deficiency in ankyrin and those with a decrease in the band 3 anion transporting protein. The presented data show that this method gives a reliable indication of altered osmotic properties of the spherocytic cells.

Hereditary spherocytosis: identification of several HS families with ankyrin and band 3 deficiency in a population of southwestern Poland

Red blood cells of 17 patients out of seven families diagnosed with HS from the southwest of Poland were studied. In six families a deficiency of ankyrin was detected, and in one family a band 3 (anion-exchanger protein) deficiency was detected. Patients from six families with the ankyrin deficiency had a 19-51% decrease in ankyrin 2.1, while the family with the band 3 deficiency showed a 33% decrease in this protein content. All changes were statistically significant, as analysed by the Student t test (P<0.05). Analysis of haemolysis kinetics gives a reliable indication of altered osmotic properties of the spherocytic cells.