MUC1 oncoprotein regulates Bcr-Abl stability and pathogenesis in chronic myelogenous leukemia cells

Integrating Clinical Cancer and PTM Proteomics Data Identifies a Mechanism of ACK1 Kinase Activation

Beyond the most common oncogenes activated by mutation (mut-drivers), there likely exists a variety of low-frequency mut-drivers, each of which is a possible frontier for targeted therapy. To identify new and understudied mut-drivers, we developed a machine learning (ML) model that integrates curated clinical cancer data and posttranslational modification (PTM) proteomics databases. We applied the approach to 62,746 patient cancers spanning 84 cancer types and predicted 3,964 oncogenic mutations across 1,148 genes, many of which disrupt PTMs of known and unknown function. The list of putative mut-drivers includes established drivers and others with poorly understood roles in cancer. This ML model is available as a web application. As a case study, we focused the approach on nonreceptor tyrosine kinases (NRTK) and found a recurrent mutation in activated CDC42 kinase-1 (ACK1) that disrupts the Mig6 homology region (MHR) and ubiquitin-association (UBA) domains on the ACK1 C-terminus. By studying these domains in cultured cells, we found that disruption of the MHR domain helps activate the kinase while disruption of the UBA increases kinase stability by blocking its lysosomal degradation. This ACK1 mutation is analogous to lymphoma-associated mutations in its sister kinase, TNK1, which also disrupt a C-terminal inhibitory motif and UBA domain. This study establishes a mut-driver discovery tool for the research community and identifies a mechanism of ACK1 hyperactivation shared among ACK family kinases.

IMPLICATIONS

This research identifies a potentially targetable activating mutation in ACK1 and other possible oncogenic mutations, including PTM-disrupting mutations, for further study.

Amsacrine downregulates BCL2L1 expression and triggers apoptosis in human chronic myeloid leukemia cells through the SIDT2/NOX4/ERK/HuR pathway

Accumulating evidence indicates that the anticancer activity of acridine derivatives is mediated through the regulation of anti-apoptotic and pro-apoptotic BCL2 protein expression. Therefore, we investigated whether the cytotoxicity of amsacrine with an acridine structural scaffold in human chronic myeloid leukemia (CML) K562 cells was mediated by BCL2 family proteins. Amsacrine induced apoptosis, mitochondrial depolarization, and BCL2L1 (also known as BCL-XL) downregulation in K562 cells. BCL2L1 overexpression inhibited amsacrine-induced cell death and mitochondrial depolarization. Amsacrine treatment triggered SIDT2-mediated miR-25 downregulation, leading to increased NOX4-mediated ROS production. ROS-mediated inactivation of ERK triggered miR-22 expression, leading to increased HuR mRNA decay. As HuR is involved in stabilizing BCL2L1 mRNA, downregulation of BCL2L1 was noted in K562 cells after amsacrine treatment. In contrast, amsacrine-induced BCL2L1 downregulation was alleviated by restoring ERK phosphorylation and HuR expression. Altogether, the results of this study suggest that amsacrine triggers apoptosis in K562 cells by inhibiting BCL2L1 expression through the SIDT2/NOX4/ERK-mediated downregulation of HuR. Furthermore, a similar pathway also explains the cytotoxicity of amsacrine in CML MEG-01 and KU812 cells.

Mucin 4 (MUC4) Protein is Expressed in B-Acute Lymphoblastic Leukemia (B-ALL) and is restricted to BCR::ABL1 Positive and BCR::ABL-like Subtypes

Mucin 4 (MUC4) is a transmembrane mucin that, like most mucins, is not expressed in normal hematopoietic cells but little is known about its expression in malignant hematopoiesis. B-Acute Lymphoblastic Leukemia (B-ALL) consists of genetically distinct disease subtypes with similarities and differences in gene expression most frequently studied at the mRNA level, which is less amenable to widespread routine clinical use. Here, we demonstrate using immunohistochemistry (IHC) that MUC4 protein is expressed in less than 10% of B-ALL with expression restricted to BCR::ABL1+ and BCR::ABL1-like (CRLF2 rearranged) subtypes of B-ALL (4/13, 31%). None (0/36, 0%) of the remaining B-ALL subtypes expressed MUC4. We compare clinical and pathologic features of MUC4+ and MUC4- BCR::ABL1+/like cases and most significantly report a possible shorter time to relapse for MUC4+ BCR::ABL1 B-ALL that would need to be validated in larger studies. In conclusion, MUC4 is a specific, albeit insensitive, marker for these high-risk subtypes of B-ALL. We propose that MUC4 IHC may be employed diagnostically to rapidly identify these B-ALL subtypes particularly in resource limited settings or when an aspirate sample is not available for ancillary genetic studies.

AMPK inhibition induces MCL1 mRNA destabilization via the p38 MAPK/miR-22/HuR axis in chronic myeloid leukemia cells

The oncogenic and tumor-suppressive roles of AMPK in chronic myeloid leukemia (CML) are controvertible. This study aimed to investigate the cytotoxic effects of the AMPK inhibitor Compound C in the CML cell lines K562, KU812, and MEG-01. Compared to K562 cells, KU812 and MEG-01 cells were more sensitive to Compound C-mediated cytotoxicity. Moreover, Compound C induced SIRT3 upregulation in K562 cells but not in KU812 or MEG-01 cells. SIRT3 silencing increased the sensitivity of K562 cells to Compound C. Additionally; Compound C-induced autophagy attenuated its induced apoptosis in KU812 and MEG-01 cells. Compound C-induced ROS-mediated AMPKα inactivation resulted in the downregulation of apoptotic regulator MCL1 in KU812 and MEG-01 cells. Mechanistically, AMPK inhibition activated p38 MAPK-mediated miR-22 expression, which in turn inhibited HuR expression, thereby reducing MCL1 mRNA stability. Overexpression of constitutively active AMPKα1 and abolishment of the activation of p38 MAPK inhibited Compound C-induced cell death and MCL1 downregulation. Furthermore, Compound C synergistically enhanced the cytotoxicity of BCR-ABL inhibitors and the BCL2 inhibitor ABT-199. Collectively, this study indicates that Compound C induces MCL1 downregulation through the AMPK/p38 MAPK/miR-22/HuR pathway, thereby inducing apoptosis of KU812 and MEG-01 cells. Furthermore, our findings suggest that AMPK inhibition is a promising strategy for improving CML therapy.

MUC4 expression by immunohistochemistry is a specific marker for BCR-ABL1+ and BCR-ABL1-like B-lymphoblastic leukemia

BCR-ABL1-like B-acute lymphoblastic leukemia (B-ALL) is a genetically heterogeneous group of high-risk B-ALL that benefits from targeted tyrosine kinase inhibitor (TKI) therapy. The incidence of this high-risk B-ALL is relatively low and screening with surrogate markers will be useful to identify patients for further genetic testing. Here we demonstrate that widely available MUC4 protein immunohistochemistry (IHC) is predictive of a BCR-ABL1-like genotype for a subset of patients. Overall, MUC4 expression was observed in 36% (9/25) BCR-ABL1-like, 43% (3/7) BCR-ABL1+ and 9% (2/22) B-ALL other cases (p=.019 for BCR-ABL1 like and BCR-ABL1+ versus B-ALL others). Furthermore, 83% (5/6) of patients with ABL class fusions showed MUC4 expression when compared to 25% (4/16, p=.006) patients with JAK class fusions. Overall, the study demonstrates that MUC4 expression is highly specific (90.9%) for BCR-ABL1+ and BCR-ABL1-like B-ALL with high sensitivity for cases with ABL class fusions.

p19INK4d inhibits proliferation and enhances imatinib efficacy through BCR-ABL signaling pathway in chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a kind of myeloproliferative disorder caused by a constitutively active BCR-ABL tyrosine kinase. Tyrosine kinase inhibitors (TKIs), imatinib and its derivatives, have achieved great progress in the treatment of CML. However, many CML patients do not respond to TKIs alone. p19^INK4d, a cyclin-dependent kinase inhibitor, plays important roles in proliferation, DNA damage repair, apoptosis and cell differentiation, but its role in CML is unknown. Herein, we found that the expression of p19^INK4d in CML patients was significantly lower than that in healthy controls. p19^INK4d overexpression inhibits cell proliferation through cell cycle arrest, and cooperates with imatinib to inhibit CML more effectively in vitro and in vivo. Mechanistically, p19^INK4d decreased the expression of BCR-ABL and its downstream molecules p-Mek1/2, moreover, the expression of Gli-1, c-myc, MUC1, Shh and TC48 also reduced significantly. Collectively, p19^INK4d inhibits proliferation and enhances imatinib efficacy in the treatment of CML. These findings maybe have implications for developing potential targets to increase imatinib sensitivity for CML.

Regulatory Molecules and Corresponding Processes of BCR-ABL Protein Degradation

The BCR-ABL fusion protein with strong tyrosine kinase activity is one of the molecular biological bases of leukemia. Imatinib (Gleevec), a specific targeted drug for the treatment of chronic myeloid leukemia (CML), was developed for inhibiting the kinase activity of the BCR-ABL fusion protein. Despite the positive clinical efficacy of imatinib, the proportion of imatinib resistance has gradually increased. The main reason for the resistance is a decrease in sensitivity to imatinib caused by mutation or amplification of the BCR-ABL gene. In response to this phenomenon, the new generation of tyrosine kinase inhibitors (TKIs) targeting the BCR-ABL fusion protein was developed to solve the problem. However this strategy only selectively inhibits the tyrosine kinase activity of the BCR-ABL protein without eliminating the BCR-ABL protein, it does not fundamentally cure the BCR-ABL-positive leukemia patients. With the accumulation of the knowledge of cellular molecular biology, it has become possible to specifically eliminate certain proteins by cellular proteases in a specific way. Therefore, the therapeutic strategy to induce the degradation of the BCR-ABL fusion protein is superior to the strategy of inhibiting its activity. The protein degradation strategy is also a solution to the TKI resistance caused by different BCR-ABL gene point mutations. In order to provide possible exploration directions and clues for eliminating the BCR-ABL fusion protein in tumor cells, we summarize the significant molecules involved in the degradation pathway of the BCR-ABL protein, as well as the reported potent compounds that can target the BCR-ABL protein for degradation.

CD69 partially inhibits apoptosis and erythroid differentiation via CD24, and their knockdown increase imatinib sensitivity in BCR-ABL-positive cells

Chronic myeloid leukemia (CML) is caused by a constitutively active BCR-ABL tyrosine kinase. Tyrosine kinase inhibitors (TKIs) imatinib and its derivatives represent a breakthrough for CML therapy, but the use of TKI alone is ineffective for many CML patients. CD69, an early activation marker of lymphocytes, participates in immune and inflammatory responses. Previous studies revealed that BCR-ABL upregulates CD69 expression; however, the role of CD69 in CML cells is unknown. Here, we demonstrate that BCR-ABL induced CD69 promoter activity and mRNA and protein expression via the NF-κB pathway. CD69 knockdown partially increased apoptosis and expression of erythroid differentiation markers, α-globin, ζ-globin, and glycophorin A, and increased imatinib sensitivity in K562 and KU812 CML cells. Gene microarray analysis and quantitative real-time PCR verified that CD24, an oncogenic gene, downregulated in K562 cells upon CD69 knockdown. CD69 overexpression increased, whereas CD69 knockdown inhibited CD24 promoter activity and mRNA and protein levels. CD24 knockdown also partially increased apoptosis, erythroid differentiation, and imatinib sensitivity in K562 cells, whereas its overexpression inhibited the effects of CD69 knockdown on apoptosis, erythroid differentiation, and imatinib sensitivity in K562 cells. Imatinib-induced apoptosis and erythroid differentiation were also inhibited by CD69 or CD24 overexpression in BCR-ABL-expressing CML cell lines and CD34⁺ cells. Taken together, CD24 is a downstream effector of CD69. CD69 and CD24 partially inhibit apoptosis and erythroid differentiation in CML cells; thus, they may be potential targets to increase imatinib sensitivity.

Mucins: Structural diversity, biosynthesis, its role in pathogenesis and as possible therapeutic targets

Mucins are the main structural components of mucus that create a selective protective barrier for epithelial surface and also execute wide range of other physiological functions. Mucins can be classified into two types, namely secreted mucins and membrane bounded mucins. Alterations in mucin expression or glycosylation and mislocalization have been seen in various types of pathological conditions such as cancers, inflammatory bowel disease and ocular disease, which highlight the importance of mucin in maintaining homeostasis. Hence mucins can be used as attractive target for therapeutic intervention. In this review, we discuss in detail about the structural diversity of mucins; their biosynthesis; its role in pathogenesis; regulation and as possible therapeutic targets.

Novel Antigen Targets for Immunotherapy of Acute Myeloid Leukemia

Acute myeloid leukemia (AML) was the first malignancy for which immunotherapy, in the form of allogeneic hematopoietic stem cell transplantation (allo-HSCT), was integrated into the standard of care. Allo-HSCT however is an imperfect therapy associated with significant morbidity and mortality while offering only incomplete prevention of AML clinical relapse. These limitations have motivated the search for AML-related antigens that might be used as more specific and effective targets of immunotherapy. While historically such investigations have focused on protein targets expressed uniquely in AML or at significantly higher levels than in normal tissues, this article will review recent discoveries which have identified a novel selection of potential antigen targets for AML immunotherapy, such as non-protein targets including lipids and carbohydrates, neo-antigens created from genetic somatic mutations or altered splicing and post-translational modification of protein targets, together with innovative ways to target overexpressed protein targets presented by cell surface peptide-MHC complexes. These novel antigens represent promising candidates for further development as targets of AML immunotherapy.

The generation and analyses of a novel combination of recombinant adenovirus vaccines targeting three tumor antigens as an immunotherapeutic

Phenotypic heterogeneity of human carcinoma lesions, including heterogeneity in expression of tumor-associated antigens (TAAs), is a well-established phenomenon. Carcinoembryonic antigen (CEA), MUC1, and brachyury are diverse TAAs, each of which is expressed on a wide range of human tumors. We have previously reported on a novel adenovirus serotype 5 (Ad5) vector gene delivery platform (Ad5 [E1-, E2b-]) in which regions of the early 1 (E1), early 2 (E2b), and early 3 (E3) genes have been deleted. The unique deletions in this platform result in a dramatic decrease in late gene expression, leading to a marked reduction in host immune response to the vector. Ad5 [E1-, E2b-]-CEA vaccine (ETBX-011) has been employed in clinical studies as an active vaccine to induce immune responses to CEA in metastatic colorectal cancer patients. We report here the development of novel recombinant Ad5 [E1-, E2b-]-brachyury and-MUC1 vaccine constructs, each capable of activating antigen-specific human T cells in vitro and inducing antigen-specific CD4⁺ and CD8⁺ T cells in vaccinated mice. We also describe the use of a combination of the three vaccines (designated Tri-Ad5) of Ad5 [E1-, E2b-]-CEA, Ad5 [E1-, E2b-]-brachyury and Ad5 [E1-, E2b-]-MUC1, and demonstrate that there is minimal to no “antigenic competition” in in vitro studies of human dendritic cells, or in murine vaccination studies. The studies reported herein support the rationale for the application of Tri-Ad5 as a therapeutic modality to induce immune responses to a diverse range of human TAAs for potential clinical studies.

Reflections on MUC1 glycoprotein: the hidden potential of isoforms in carcinogenesis

Mucin 1 (MUC1) has been described as the renaissance molecule due to the large set of functions it displays in both normal and neoplastic cells. This membrane-tethered glycoprotein is overexpressed and aberrantly glycosylated in most epithelial cancers, being involved in several processes related with malignant phenotype acquisition. With a highly polymorphic structure, both in the polypeptide and glycan counterparts, MUC1 variability has been associated with susceptibility to several diseases, including cancer. Biochemical features and biological functions have been characterized upon the full-length MUC1 protein, remaining to clarify the real impact on cell dynamics of the plethora of MUC1 isoforms. This review aims to encompass a detailed characterization of MUC1 role in carcinogenesis, highlighting recent findings in cell differentiation and uncovering new evidences of MUC1 isoforms involvement in malignant phenotype.

MUC1 in hematological malignancies

Mucin1 (MUC1) is a transmembrane oncogenic protein that plays a central role in malignant transformation and disease evolution, including cell proliferation, survival, self-renewal, and metastatic invasion. MUC1 has been shown to interact with diverse effectors such as β-catenin, receptor tyrosine kinases, and c-Abl, which are of importance in the pathogenesis of various hematological malignancies. In myeloid leukemia, MUC1 has been shown to have an essential role in leukemia stem-cell function, the induction of reactive oxygen species (ROS), and the promotion of terminal myeloid differentiation. As such, MUC1 is an attractive therapeutic target in hematologic malignancies. Targeting MUC1 has been shown to be an effective approach for inducing cell death in tumor in in vivo and in vitro models. Furthermore, MUC1 inhibition is synergistic with other therapeutic agents in the treatment of hematologic disorders. This review will explore the role of MUC1 in hematological malignancies, and strategies for targeting this oncoprotein.

Enhancing potency of siRNA targeting fusion genes by optimization outside of target sequence

Canonical siRNA design algorithms have become remarkably effective at predicting favorable binding regions within a target mRNA, but in some cases (e.g., a fusion junction site) region choice is restricted. In these instances, alternative approaches are necessary to obtain a highly potent silencing molecule. Here we focus on strategies for rational optimization of two siRNAs that target the junction sites of fusion oncogenes BCR-ABL and TMPRSS2-ERG. We demonstrate that modifying the termini of these siRNAs with a terminal G-U wobble pair or a carefully selected pair of terminal asymmetry-enhancing mismatches can result in an increase in potency at low doses. Importantly, we observed that improvements in silencing at the mRNA level do not necessarily translate to reductions in protein level and/or cell death. Decline in protein level is also heavily influenced by targeted protein half-life, and delivery vehicle toxicity can confound measures of cell death due to silencing. Therefore, for BCR-ABL, which has a long protein half-life that is difficult to overcome using siRNA, we also developed a nontoxic transfection vector: poly(lactic-coglycolic acid) nanoparticles that release siRNA over many days. We show that this system can achieve effective killing of leukemic cells. These findings provide insights into the implications of siRNA sequence for potency and suggest strategies for the design of more effective therapeutic siRNA molecules. Furthermore, this work points to the importance of integrating studies of siRNA design and delivery, while heeding and addressing potential limitations such as restricted targetable mRNA regions, long protein half-lives, and nonspecific toxicities.

Stat5 Exerts Distinct, Vital Functions in the Cytoplasm and Nucleus of Bcr-Abl+ K562 and Jak2(V617F)+ HEL Leukemia Cells

Signal transducers and activators of transcription (Stats) play central roles in the conversion of extracellular signals, e.g., cytokines, hormones and growth factors, into tissue and cell type specific gene expression patterns. In normal cells, their signaling potential is strictly limited in extent and duration. The persistent activation of Stat3 or Stat5 is found in many human tumor cells and contributes to their growth and survival. Stat5 activation plays a pivotal role in nearly all hematological malignancies and occurs downstream of oncogenic kinases, e.g., Bcr-Abl in chronic myeloid leukemias (CML) and Jak2(V617F) in other myeloproliferative diseases (MPD). We defined the mechanisms through which Stat5 affects growth and survival of K562 cells, representative of Bcr-Abl positive CML, and HEL cells, representative for Jak2(V617F) positive acute erythroid leukemia. In our experiments we suppressed the protein expression levels of Stat5a and Stat5b through shRNA mediated downregulation and demonstrated the dependence of cell survival on the presence of Stat5. Alternatively, we interfered with the functional capacities of the Stat5 protein through the interaction with a Stat5 specific peptide ligand. This ligand is a Stat5 specific peptide aptamer construct which comprises a 12mer peptide integrated into a modified thioredoxin scaffold, S5-DBD-PA. The peptide sequence specifically recognizes the DNA binding domain (DBD) of Stat5. Complex formation of S5-DBD-PA with Stat5 causes a strong reduction of P-Stat5 in the nuclear fraction of Bcr-Abl-transformed K562 cells and a suppression of Stat5 target genes. Distinct Stat5 mediated survival mechanisms were detected in K562 and Jak2(V617F)-transformed HEL cells. Stat5 is activated in the nuclear and cytosolic compartments of K562 cells and the S5-DBD-PA inhibitor most likely affects the viability of Bcr-Abl⁺ K562 cells through the inhibition of canonical Stat5 induced target gene transcription. In HEL cells, Stat5 is predominantly present in the cytoplasm and the survival of the Jak2(V617F)⁺ HEL cells is impeded through the inhibition of the cytoplasmic functions of Stat5.

Protein mislocalization: mechanisms, functions and clinical applications in cancer

The changes from normal cells to cancer cells are primarily regulated by genome instability, which foster hallmark functions of cancer through multiple mechanisms including protein mislocalization. Mislocalization of these proteins, including oncoproteins, tumor suppressors, and other cancer-related proteins, can interfere with normal cellular function and cooperatively drive tumor development and metastasis. This review describes the cancer-related effects of protein subcellular mislocalization, the related mislocalization mechanisms, and the potential application of this knowledge to cancer diagnosis, prognosis, and therapy.

The adenocarcinoma cell surface mucin receptor for alpha-fetoprotein: is the same receptor present on circulating monocytes and macrophages? A commentary

The mucin family of proteins is largely expressed on sedentary epithelial cells lining the gastrointestinal, pulmonary, and reproductive tracts and their associated organs and malignant tumors. It is less well-known that mucins are also expressed on circulatory cells of the immune and inflammatory systems, such as monocytes, macrophages, leukemic, and lymphoma cells. The epithelial mucins function in (a) protection and lubrication of mucosal linings, (b) cell adhesion and cell-to-cell contact, (c) cell migration and metastasis, and (d) signal transduction. It would be logical to presume that mucins expressed on circulating mononuclear cells could perform similar functions. Recently, it was proposed that the alpha-fetoprotein (AFP) receptor, known to be present on solid epithelial-derived malignant tumor cells, can be identified as a mucin glycoprotein. Interestingly, it was also reported that AFP binds to a receptor on circulating cells and sedentary tumor cells of lymphoreticular origin, especially monocytes associated with lymphomas and leukemias. The primary objective of the present commentary is to present literature-based evidence that some of the cell surface mucins on sedentary epithelial tumor cells and certain mucins expressed on circulating monocytes/macrophages are identical to the AFP receptor. The secondary objective is to discuss the role of AFP and its derived peptides in the growth suppression of adenocarcinomas and lymphomas using the AFP-mucin receptor concept as a key to the mechanism of tumor growth inhibition.

MUC1 and maltose‑binding protein recombinant fusion protein combined with Bacillus Calmette‑Guerin induces MUC1‑specific and nonspecific anti‑tumor immunity in mice

Human mucin 1 (MUC1) is a target for immunotherapy. The major problem associated with MUC1‑based cancer vaccines is the weakness of the immunogenicity of MUC1. The present study aimed to develop an efficient cancer vaccine through generating a recombinant fusion protein consisting of MUC1 and maltose‑binding protein (MBP) by inserting seven tandem repeats encoding the human MUC1 gene into the pMAL‑c2 expression vector. Bacillus Calmette‑Guerin (BCG) was used as an adjuvant. MUC1 was found to predominantly induce T helper type 2 (Th2) cell responses. MUC1/BCG and MUC1‑MBP were found to generate T helper (Th) type 1 and 2 responses, while MUC1‑MBP/BCG induced a Th1 immune profile and stimulated MUC1‑specific cytotoxic T lymphocyte killing activity. MUC1‑MBP, as well as MBP and BCG alone were found to induce natural killer (NK) cell activity, with MUC1‑MBP/BCG observed to synergistically induce NK cell activity. Furthermore, MUC1‑MBP/BCG significantly inhibited MUC1+ B16 cell growth in mice. These findings show that MBP augments the immunogenicity of MUC1 and that BCG enhances the efficacy of the MUC1‑MBP vaccine. Thus, MUC1‑MBP/BCG may have potential as a cancer vaccine for clinical application.

Identification and characterization of agonist epitopes of the MUC1-C oncoprotein

The MUC1 tumor-associated antigen is overexpressed in the majority of human carcinomas and several hematologic malignancies. Much attention has been paid to the hypoglycosylated variable number of tandem repeats (VNTR) region of the N-terminus of MUC1 as a vaccine target, and recombinant viral vector vaccines are also being evaluated that express the entire MUC1 transgene. While previous studies have described MUC1 as a tumor-associated tissue differentiation antigen, studies have now determined that the C-terminus of MUC1 (MUC1-C) is an oncoprotein, and its expression is an indication of poor prognosis in numerous tumor types. We report here the identification of nine potential CD8⁺ cytotoxic T lymphocyte epitopes of MUC1, seven in the C-terminus and two in the VNTR region, and have identified enhancer agonist peptides for each of these epitopes. These epitopes span HLA-A2, HLA-A3, and HLA-A24 major histocompatibility complex (MHC) class I alleles, which encompass the majority of the population. The agonist peptides, compared to the native peptides, more efficiently (a) generate T-cell lines from the peripheral blood mononuclear cells of cancer patients, (b) enhance the production of IFN-γ by peptide-activated human T cells, and (c) lyse human tumor cell targets in an MHC-restricted manner. The agonist epitopes described here can be incorporated into various vaccine platforms and for the ex vivo generation of human T cells. These studies provide the rationale for the T-cell-mediated targeting of the oncogenic MUC1-C, which has been shown to be an important factor in both drug resistance and poor prognosis for numerous tumor types.

Disrupting BCR-ABL in combination with secondary leukemia-specific pathways in CML cells leads to enhanced apoptosis and decreased proliferation

Chronic myeloid leukemia (CML) is a myeloproliferative disorder caused by expression of the fusion gene BCR-ABL following a chromosomal translocation in the hematopoietic stem cell. Therapeutic management of CML uses tyrosine kinase inhibitors (TKIs), which block ABL-signaling and effectively kill peripheral cells with BCR-ABL. However, TKIs are not curative, and chronic use is required in order to treat CML. The primary failure for TKIs is through the development of a resistant population due to mutations in the TKI binding regions. This led us to develop the mutant coiled-coil, CC(mut2), an alternative method for BCR-ABL signaling inhibition by targeting the N-terminal oligomerization domain of BCR, necessary for ABL activation. In this article, we explore additional pathways that are important for leukemic stem cell survival in K562 cells. Using a candidate-based approach, we test the combination of CC(mut2) and inhibitors of unique secondary pathways in leukemic cells. Transformative potential was reduced following silencing of the leukemic stem cell factor Alox5 by RNA interference. Furthermore, blockade of the oncogenic protein MUC-1 by the novel peptide GO-201 yielded reductions in proliferation and increased cell death. Finally, we found that inhibiting macroautophagy using chloroquine in addition to blocking BCR-ABL signaling with the CC(mut2) was most effective in limiting cell survival and proliferation. This study has elucidated possible combination therapies for CML using novel blockade of BCR-ABL and secondary leukemia-specific pathways.

MUC1c regulates cell survival in pancreatic cancer by preventing lysosomal permeabilization

BACKGROUND

MUC1 is a type I transmembrane glycoprotein aberrantly overexpressed in various cancer cells including pancreatic cancer. The cytosolic end of MUC1 (MUC1-c) is extensively involved in a number of signaling pathways. MUC1-c is reported to inhibit apoptosis in a number of cancer cells, but the mechanism of inhibition is unclear.

METHOD

Expression of MUC1-c was studied in the pancreatic cancer cell line MIAPaCa-2 at the RNA level by using qRTPCR and at the protein level by Western blotting. MUC1-c expression was inhibited either by siRNA or by a specific peptide inhibitor, GO-201. Effect of MUC1-c inhibition on viability and proliferation and lysosomal permeabilization were studied. Association of MUC1-c with HSP70 was detected by co-immunoprecipitation of MUC1-c and HSP70. Localization of MUC1-c in cellular organelles was monitored by immunofluorescence and with immuno- blotting by MUC1-c antibody after subcellular fractionation.

RESULTS

Inhibition of MUC1-c by an inhibitor (GO-201) or siRNA resulted in reduced viability and reduced proliferation of pancreatic cancer cells. Furthermore, GO-201, the peptide inhibitor of MUC1-c, was effective in reducing tumor burden in pancreatic cancer mouse model. MUC1-c was also found to be associated with HSP70 in the cytosol, although a significant amount of MUC1 was also seen to be present in the lysosomes. Inhibition of MUC1 expression or activity showed an enhanced Cathepsin B activity in the cytosol, indicating lysosomal permeabilization. Therefore this study indicates that MUC1-c interacted with HSP70 in the cytosol of pancreatic cancer cells and localized to the lysosomes in these cells. Further, our results showed that MUC1-c protects pancreatic cancer cells from cell death by stabilizing lysosomes and preventing release of Cathepsin B in the cytosol.

MUC1-C Oncoprotein Blocks Terminal Differentiation of Chronic Myelogenous Leukemia Cells by a ROS-Mediated Mechanism

Chronic myelogenous leukemia (CML) inevitably progresses to a blast phase by mechanisms that are not well understood. The MUC1-C oncoprotein is expressed in CML blasts but not chronic phase cells. The present studies demonstrate that treatment of KU812 and K562 CML cells with a cell-penetrating MUC1-C inhibitor, designated GO-203, is associated with increases in reactive oxygen species (ROS) and depletion of glutathione. GO-203 treatment resulted in the complete downregulation of Bcr-Abl expression and induced cell cycle arrest by a ROS-mediated mechanism that was blocked by the antioxidant N-acetylcysteine. Progression of CML to blast crisis has been linked to dysregulation of Wnt/β-catenin signaling and an arrest of differentiation. The present results show that inhibition of MUC1-C induces ROS-mediated suppression of β-catenin expression and induction of a differentiated myeloid phenotype. Our studies also show that GO-203 treatment is associated with ROS-induced decreases in ATP and loss of survival by late apoptosis/necrosis. These findings demonstrate that inhibition of the MUC1-C oncoprotein in CML cells disrupts redox balance and thereby 1) downregulates expression of both Bcr-Abl and β-catenin and 2) induces terminal myeloid differentiation by ROS-mediated mechanisms.

MUC1-C oncoprotein suppresses reactive oxygen species-induced terminal differentiation of acute myelogenous leukemia cells

Acute myeloid leukemia (AML) cells are characterized by unlimited self-renewal and an impaired capacity to undergo terminal differentiation. The MUC1 oncoprotein is aberrantly expressed in AML cells; however, there has been no evidence for involvement of MUC1 in myeloid leukemogenesis. Cell-penetrating peptide inhibitors of the MUC1-C subunit block its oligomerization and thereby oncogenic function. The present results demonstrate that treatment of human MOLM-14 and MV4-11 AML cells with these inhibitors is associated with arrest of growth, induction of late apoptosis/necrosis, and loss of self-renewal capacity. Similar results were obtained with primary blasts from patients with AML. Inhibition of MUC1-C was associated with increases in reactive oxygen species (ROS) and depletion of glutathione. Increases in ROS have been linked to induction of hematopoietic cell differentiation along the myeloid lineage. In this regard, inhibition of MUC1-C was associated with induction of a terminally differentiated myeloid phenotype in AML cell lines and primary blasts by an ROS-dependent mechanism. These findings indicate that MUC1-C function is of importance to AML cell self-renewal and that inhibition of MUC1-C represents a potential therapeutic approach to induce terminal differentiation of AML cells.

MUC1-C oncoprotein promotes STAT3 activation in an autoinductive regulatory loop

Signal transducer and activator of transcription 3 (STAT3) is activated in human breast cancer and other malignancies. Mucin 1 (MUC1) is a heterodimeric cell surface glycoprotein that is overexpressed in human carcinomas and, like STAT3, promotes cell survival and induces transformation. We found that in breast cancer cells, the MUC1 carboxyl-terminal receptor subunit (MUC1-C) associates with the gp130-Janus-activated kinase 1 (JAK1)-STAT3 complex. The MUC1-C cytoplasmic domain interacted directly with JAK1 and STAT3, and MUC1-C was necessary for JAK1-mediated STAT3 activation. In turn, MUC1-C and activated STAT3 occupied the promoter of MUC1, and MUC1-C contributed to STAT3-mediated activation of MUC1 transcription. The MUC1-C inhibitor GO-201 blocked the MUC1-C interaction with STAT3, thereby decreasing MUC1-C and STAT3 occupancy on the MUC1 and STAT3 promoters and activation of STAT3 target genes, including MUC1 itself. These findings indicate that MUC1-C promotes STAT3 activation and that MUC1-C and STAT3 function in an autoinductive loop that may play a role in cancer cell survival.

ABL fusion oncogene transformation and inhibitor sensitivity are mediated by the cellular regulator RIN1

ABL gene translocations create constitutively active tyrosine kinases that are causative in chronic myeloid leukemia, acute lymphocytic leukemia and other hematopoietic malignancies. Consistent retention of ABL SH3/SH2 autoinhibitory domains, however, suggests that these leukemogenic tyrosine kinase fusion proteins remain subject to regulation. We resolve this paradox, demonstrating that BCR-ABL1 kinase activity is regulated by RIN1, an ABL SH3/SH2 binding protein. BCR-ABL1 activity was increased by RIN1 overexpression and decreased by RIN1 silencing. Moreover, Rin1(-/-) bone marrow cells were not transformed by BCR-ABL1, ETV6-ABL1 or BCR-ABL1(T315I), a patient-derived drug-resistant mutant, as judged by growth factor independence. Rescue by ectopic RIN1 verified a cell autonomous mechanism of collaboration with BCR-ABL1 during transformation. Sensitivity to the ABL kinase inhibitor imatinib was increased by RIN1 silencing, consistent with RIN1 stabilization of an activated BCR-ABL1 conformation having reduced drug affinity. The dependence on activation by RIN1 to unleash full catalytic and cell transformation potential reveals a previously unknown vulnerability that could be exploited for treatment of leukemic cases driven by ABL translocations. The findings suggest that RIN1 targeting could be efficacious for imatinib-resistant disease and might complement ABL kinase inhibitors in first-line therapy.

Terminal differentiation of chronic myelogenous leukemia cells is induced by targeting of the MUC1-C oncoprotein

Chronic myelogenous leukemia (CML) is caused by expression of the Bcr-Abl fusion protein in hematopoietic stem cells. The MUC1-C oncoprotein is expressed in CML blasts and stabilizes Bcr-Abl. The present studies demonstrate that treatment of KU812 and K562 CML cells with GO-201, a cell-penetrating peptide inhibitor of MUC1-C oligomerization, downregulates Bcr-Abl expression and inhibits cell growth. In concert with decreases in Bcr-Abl levels, KU812 and K562 cells responded to GO-201 with induction of a differentiated myeloid phenotype as evidenced by increased expression of CD11b, CD11c and CD14. The results also show that the GO-201-treated cells undergo a late apoptotic/necrotic response, consistent with induction of terminal differentiation. Primary CML blasts expressing MUC1 similarly responded to GO-201 with induction of a more differentiated phenotype and late apoptosis/necrosis. In addition, treatment of KU812 xenografts in nude mice was associated with upregulation of CD11 and tumor regression. These findings indicate that CML blasts respond to targeting of the MUC1-C oncoprotein with induction of terminal differentiation.

Expression of a Src family kinase in chronic myelogenous leukemia cells induces resistance to imatinib in a kinase-dependent manner

The Bcr-Abl kinase inhibitor imatinib is remarkably effective in chronic myelogenous leukemia (CML), although drug resistance is an emerging problem. Myeloid Src family kinases such as Hck and Lyn are often overexpressed in imatinib-resistant CML cells that lack Bcr-Abl mutations. Here we tested whether Hck overexpression is sufficient to induce imatinib resistance using both wild-type Hck and a mutant (Hck-T338A) that is uniquely sensitive to the pyrazolo-pyrimidine inhibitor, NaPP1. Expression of either kinase in K562 CML cells caused resistance to imatinib-induced apoptosis and inhibition of soft-agar colony formation. Treatment with NaPP1 restored sensitivity to imatinib in cells expressing T338A but not wild-type Hck, demonstrating that resistance requires Hck kinase activity. NaPP1 also reduced Hck-mediated phosphorylation of Bcr-Abl at sites that may affect imatinib sensitivity exclusively in cells expressing Hck-T338A. These data show that elevated Src family kinase activity is sufficient to induce imatinib resistance through a mechanism that may involve phosphorylation of Bcr-Abl.

Mucins in cancer: function, prognosis and therapy

Epithelia are protected from adverse conditions by a mucous barrier. The secreted and transmembrane mucins that constitute the mucous barrier are largely unrecognized as effectors of carcinogenesis. However, both types of mucins are intimately involved in inflammation and cancer. Moreover, diverse human malignancies overexpress transmembrane mucins to exploit their role in signalling cell growth and survival. Mucins have thus been identified as markers of adverse prognosis and as attractive therapeutic targets. Notably, the findings that certain transmembrane mucins induce transformation and promote tumour progression have provided the experimental basis for demonstrating that inhibitors of their function are effective as anti-tumour agents in preclinical models.

14-3-3 ligand prevents nuclear import of c-ABL protein in chronic myeloid leukemia

Here we demonstrated that the 'loss of function' of not-rearranged c-ABL in chronic myeloid leukemia (CML) is promoted by its cytoplasmic compartmentalization bound to 14-3-3 sigma scaffolding protein. In particular, constitutive tyrosine kinase (TK) activity of p210 BCR-ABL blocks c-Jun N-terminal kinase (JNK) phosphorylation leading to 14-3-3 sigma phosphorylation at a critical residue (Ser(186)) for c-ABL binding in response to DNA damage. Moreover, it is associated with 14-3-3 sigma over-expression arising from epigenetic mechanisms (promoter hyper-acetylation). Accordingly, p210 BCR-ABL TK inhibition by the TK inhibitor Imatinib mesylate (IM) evokes multiple events, including JNK phosphorylation at Thr(183), p38 mitogen-activated protein kinase (MAPK) phosphorylation at Thr(180), c-ABL de-phosphorylation at Ser residues involved in 14-3-3 binding and reduction of 14-3-3 sigma expression, that let c-ABL release from 14-3-3 sigma and nuclear import, and address BCR-ABL-expressing cells towards apoptotic death. Informational spectrum method (ISM), a virtual spectroscopy method for analysis of protein interactions based on their structure, and mathematical filtering in cross spectrum (CS) analysis identified 14-3-3 sigma/c-ABL binding sites. Further investigation on CS profiles of c-ABL- and p210 BCR-ABL-containing complexes revealed the mechanism likely involved 14-3-3 precluded phosphorylation in CML cells.

The cytoplasmic tail of MUC1: a very busy place

The role of mucin 1 (MUC1) in protecting epithelia from microbial infection, enzymatic digestion, and other irritants has been appreciated for some time. In addition, MUC1 serves as a barrier to embryo implantation. MUC1 is highly abundant in many tumors in which its role in barrier function may serve to protect cells from the host immune system, whereas MUC1 is less abundant in certain other cells-for example, in trophoblasts and hematopoietic cells. Most of the functions of MUC1 depend upon its large, extracellular ectodomain. Nonetheless, a series of studies have demonstrated a surprisingly diverse role for the small, highly conserved cytoplasmic domain of MUC1 in intracellular signaling. These intracellular activities have potential roles in the physiology of both malignant and nonmalignant cells.

Transcriptional control of the expression of MUC1

MUC1 is a multifunctional cell surface glycoprotein that modulates cell adhesion, protects mucosa from infection and enzymatic attack, lubricates cell surfaces, participates in multiple signal-transduction pathways and is overexpressed by many tumors. MUC1 levels change dynamically in various cellular contexts. The primary mechanism for controlling MUC1 expression appears to be transcriptional through a complex combination of often overlapping regulatory motifs that control both tissue specificity and overall rate of transcription. This review will summarize the current knowledge of the factors known to control MUC1 transcriptional regulation, including cytokines, steroid hormones and the growth factors they stimulate, as well as suggest how this information may be exploited in the future to control MUC1 expression in specific biological contexts.

Nuclear trafficking of pro-apoptotic kinases in response to DNA damage

The cellular response to genotoxic stress includes cell-cycle arrest, activation of DNA repair and induction of apoptosis. However, the signals that determine cell fate are largely unknown. Recent studies have shown that several pro-apoptotic kinases, including protein kinase C (PKC)delta, Abelson murine leukemia viral oncogene homolog 1 (c-Abl) and dual-specificity tyrosine-phosphorylation-regulated kinase 2 (DYRK2), undergo nuclear-cytoplasmic shuttling in response to DNA damage. Importantly, whereas precise regulation for the shuttling of these kinases remains uncertain, this mechanism has consequences for induction of apoptosis and implies that proper localization is central to the function of pro-apoptotic kinases. This review highlights recent progress demonstrating that the nuclear targeting of kinases is a novel and essential regulatory mechanism that directly influences the induction of apoptosis in response to DNA damage. The potential implications for novel therapies are also discussed.

MUC1 oncoprotein promotes growth and survival of human multiple myeloma cells

The MUC1 oncoprotein is aberrantly expressed in human multiple myeloma cells by mechanisms that are not understood. Moreover, the functional role of MUC1 in multiple myeloma is not known. The present studies demonstrate that the MUC1 gene locus is amplified in multiple myeloma cell lines and in primary cells from patients. The KMS28PE multiple myeloma cell line, which was found to have MUC1 gene amplification, was stably silenced for MUC1 using different siRNAs. Silencing MUC1 was associated with a decrease in nuclear beta-catenin levels, consistent with the function of MUC1 in stabilizing beta-catenin. MUC1 is also known to activate the IKKbeta-->NF-kappaB pathway and KMS28PE cells silenced for MUC1 were found to have downregulation of IKKbeta and IkappaBalpha phosphorylation, and decreased nuclear targeting of NF-kappaB p65. The results also demonstrate that MUC1: i) contributes to KMS28PE cell proliferation, and ii) protects against apoptosis and loss of self-renewal in the response to melphalan and dexamethasone. These findings indicate that MUC1 activates the beta-catenin and NF-kappaB pathways in multiple myeloma cells and contributes to their growth and survival.