Bin1 ablation in mammary gland delays tissue remodeling and drives cancer progression

BIN1 inhibited tumor growth, metastasis and stemness by ALDH1/NOTCH pathway in bladder carcinoma

BACKGROUND

Bladder cancer (BLCA) represents one of the most prevalent urological malignancies worldwide. Bridging integrator 1 (BIN1), a well-characterized tumor suppressor that interacts with and inhibits oncogenic Myc transcription factors, has demonstrated crucial roles in various cancer types. However, its specific functions and underlying molecular mechanisms in BLCA development and progression remain poorly understood. This study aims to elucidate the role of BIN1 in regulating BLCA cell proliferation, metastasis, and cancer stem cell properties.

METHODS

Using urinary proteomics analysis, we identified BIN1 as a significantly dysregulated protein in BLCA. The clinical significance of BIN1 was further validated through comprehensive analyses of public databases. BIN1 expression levels defined distinct molecular and immunological subtypes of BLCA. Through proteomic profiling of BIN1-overexpressing UMUC3 cells and corresponding controls, we identified ALDH1 as a key downstream effector in the BIN1-regulated ALDH1/NOTCH signaling axis. We employed multiple experimental approaches, including Western blot analysis, quantitative RT-PCR, immunofluorescence staining, wound healing assays, transwell migration assays, colony formation assays, tumor sphere formation assays, flow cytometry, CCK8 proliferation assays, and cell transfection experiments.

RESULTS

We observed significant downregulation of BIN1 in both BLCA tissues and cell lines compared to normal adjacent tissues and SV-HUC-1 cells, respectively. BIN1 overexpression inhibited cancer cell proliferation by promoting apoptosis and suppressed epithelial-mesenchymal transition (EMT), thereby reducing local invasion and distant metastasis. Additionally, BIN1 regulated cancer stem cell properties through modulation of ALDH1 expression, with NOTCH2 acting as a crucial downstream mediator of ALDH1 signaling.

CONCLUSION

Our findings demonstrate that BIN1 functions as a tumor suppressor in BLCA and suggest its potential utility as both a diagnostic biomarker and therapeutic target for BLCA treatment.

BIN1 in cancer: biomarker and therapeutic target

BACKGROUND

The bridging integrator 1 (BIN1) protein was originally identified as a pro-apoptotic tumor suppressor that binds to and inhibits oncogenic MYC transcription factors. BIN1 has complex physiological functions participating in endocytosis, membrane cycling, cytoskeletal regulation, DNA repair deficiency, cell-cycle arrest, and apoptosis. The expression of BIN1 is closely related to the development of various diseases such as cancer, Alzheimer's disease, myopathy, heart failure, and inflammation.

PURPOSE

Because BIN1 is commonly expressed in terminally differentiated normal tissues and is usually undetectable in refractory or metastatic cancer tissues, this differential expression has led us to focus on human cancers associated with BIN1. In this review, we discuss the potential pathological mechanisms of BIN1 during cancer development and its feasibility as a prognostic marker and therapeutic target for related diseases based on recent findings on its molecular, cellular, and physiological roles.

CONCLUSION

BIN1 is a tumor suppressor that regulates cancer development through a series of signals in tumor progression and microenvironment. It also makes BIN1 a feasible early diagnostic or prognostic marker for cancer.

Gut-brain connections in neurodegenerative disease: immunotherapeutic targeting of Bin1 in inflammatory bowel disease and Alzheimer's disease

Longer lifespan produces risks of age-associated neurodegenerative disorders such as Alzheimer's disease (AD), which is characterized by declines in memory and cognitive function. The pathogenic causes of AD are thought to reflect a progressive aggregation in the brain of amyloid plaques composed of beta-amyloid (Aß) peptides and neurofibrillary tangles composed of phosphorylated tau protein. Recently, long-standing investigations of the Aß disease hypothesis gained support via a passive immunotherapy targeting soluble Aß protein. Tau-targeting approaches using antibodies are also being pursued as a therapeutic approach to AD. In genome-wide association studies, the disease modifier gene Bin1 has been identified as a top risk factor for late-onset AD in human populations, with recent studies suggesting that Bin1 binds tau and influences its extracellular deposition. Interestingly, before AD emerges in the brain, tau levels rise in the colon, where Bin1-a modifier of tissue barrier function and inflammation-acts to promote inflammatory bowel disease (IBD). This connection is provocative given clinical evidence of gut-brain communication in age-associated neurodegenerative disorders, including AD. In this review, we discuss a Bin1-targeting passive immunotherapy developed in our laboratory to treat IBD that may offer a strategy to indirectly reduce tau deposition and limit AD onset or progression.

Trial watch: IDO inhibitors in cancer therapy

Indoleamine 2,3-dioxygenase 1 (IDO1) catalyzes the first, rate-limiting step of the so-called “kynurenine pathway”, which converts the essential amino acid L-tryptophan (Trp) into the immunosuppressive metabolite L-kynurenine (Kyn). While expressed constitutively by some tissues, IDO1 can also be induced in specific subsets of antigen-presenting cells that ultimately favor the establishment of immune tolerance to tumor antigens. At least in part, the immunomodulatory functions of IDO1 can be explained by depletion of Trp and accumulation of Kyn and its derivatives. In animal tumor models, genetic or pharmacological IDO1 inhibition can cause the (re)activation of anticancer immune responses. Similarly, neoplasms expressing high levels of IDO1 may elude anticancer immunosurveillance. Therefore, IDO1 inhibitors represent promising therapeutic candidates for cancer therapy, and some of them have already entered clinical evaluation. Here, we summarize preclinical and clinical studies testing IDO1-targeting interventions for oncologic indications.

Cardiac-specific disruption of Bin1 in mice enables a model of stress- and age-associated dilated cardiomyopathy

Non-compensated dilated cardiomyopathy (DCM) leading to death from heart failure is rising rapidly in developed countries due to aging demographics, and there is a need for informative preclinical models to guide the development of effective therapeutic strategies to prevent or delay disease onset. In this study, we describe a novel model of heart failure based on cardiac-specific deletion of the prototypical mammalian BAR adapter-encoding gene Bin1, a modifier of age-associated disease. Bin1 deletion during embryonic development causes hypertrophic cardiomyopathy and neonatal lethality, but there is little information on how Bin1 affects cardiac function in adult animals. Here we report that cardiomyocyte-specific loss of Bin1 causes age-associated dilated cardiomyopathy (DCM) beginning by 8-10 months of age. Echocardiographic analysis showed that Bin1 loss caused a 45% reduction in ejection fraction during aging. Younger animals rapidly developed DCM if cardiac pressure overload was created by transverse aortic constriction. Heterozygotes exhibited an intermediate phenotype indicating Bin1 is haplo-insufficient to sustain normal heart function. Bin1 loss increased left ventricle (LV) volume and diameter during aging, but it did not alter LV volume or diameter in hearts from heterozygous mice nor did it affect LV mass. Bin1 loss increased interstitial fibrosis and mislocalization of the voltage-dependent calcium channel Cav 1.2, and the lipid raft scaffold protein caveolin-3, which normally complexes with Bin1 and Cav 1.2 in cardiomyocyte membranes. Our findings show how cardiac deficiency in Bin1 function causes age- and stress-associated heart failure, and they establish a new preclinical model of this terminal cardiac disease.

BIN1 regulates BACE1 intracellular trafficking and amyloid-β production

BIN1 is a genetic risk factor of late-onset Alzheimer disease (AD), which was identified in multiple genome-wide association studies. BIN1 is a member of the amphiphysin family of proteins, and contains N-terminal Bin-Amphiphysin-Rvs and C-terminal Src homology 3 domains. BIN1 is widely expressed in the mouse and human brains, and has been reported to function in the endocytosis and the endosomal sorting of membrane proteins. BACE1 is a type 1 transmembrane aspartyl protease expressed predominantly in neurons of the brain and responsible for the production of amyloid-β peptide (Aβ). Here we report that the depletion of BIN1 increases cellular BACE1 levels through impaired endosomal trafficking and reduces BACE1 lysosomal degradation, resulting in increased Aβ production. Our findings provide a mechanistic role of BIN1 in the pathogenesis of AD as a novel genetic regulator of BACE1 levels and Aβ production.

Elevated NIBP/TRAPPC9 mediates tumorigenesis of cancer cells through NFκB signaling

Regulatory mechanisms underlying constitutive and inducible NFκB activation in cancer remain largely unknown. Here we investigated whether a novel NIK- and IKK2-binding protein (NIBP) is required for maintaining malignancy of cancer cells in an NFκB-dependent manner. Real-time polymerase chain reaction analysis of a human cancer survey tissue-scan cDNA array, immunostaining of a human frozen tumor tissue array and immunoblotting of a high-density reverse-phase cancer protein lysate array showed that NIBP is extensively expressed in most tumor tissues, particularly in breast and colon cancer. Lentivirus-mediated NIBP shRNA knockdown significantly inhibited the growth/proliferation, invasion/migration, colony formation and xenograft tumorigenesis of breast (MDA-MB-231) or colon (HCT116) cancer cells. NIBP overexpression in HCT116 cells promoted cell proliferation, migration and colony formation. Mechanistically, NIBP knockdown in cancer cells inhibited cytokine-induced activation of NFκB luciferase reporter, thus sensitizing the cells to TNFα-induced apoptosis. Endogenous NIBP bound specifically to the phosphorylated IKK2 in a TNFα-dependent manner. NIBP knockdown transiently attenuated TNFα-stimulated phosphorylation of IKK2/p65 and degradation of IκBα. In contrast, NIBP overexpression enhanced TNFα-induced NFκB activation, thus inhibiting constitutive and TNFα-induced apoptosis. Collectively, our data identified important roles of NIBP in promoting tumorigenesis via NFκΒ signaling, spotlighting NIBP as a promising target in cancer therapeutic intervention.

Isoproterenol Promotes Rapid Ryanodine Receptor Movement to Bridging Integrator 1 (BIN1)-Organized Dyads

BACKGROUND

The key pathophysiology of human acquired heart failure is impaired calcium transient, which is initiated at dyads consisting of ryanodine receptors (RyRs) at sarcoplasmic reticulum apposing CaV1.2 channels at t-tubules. Sympathetic tone regulates myocardial calcium transients through β-adrenergic receptor (β-AR)-mediated phosphorylation of dyadic proteins. Phosphorylated RyRs (P-RyR) have increased calcium sensitivity and open probability, amplifying calcium transient at a cost of receptor instability. Given that bridging integrator 1 (BIN1) organizes t-tubule microfolds and facilitates CaV1.2 delivery, we explored whether β-AR-regulated RyRs are also affected by BIN1.

METHODS AND RESULTS

Isolated adult mouse hearts or cardiomyocytes were perfused for 5 minutes with the β-AR agonist isoproterenol (1 µmol/L) or the blockers CGP+ICI (baseline). Using biochemistry and superresolution fluorescent imaging, we identified that BIN1 clusters P-RyR and CaV1.2. Acute β-AR activation increases coimmunoprecipitation between P-RyR and cardiac spliced BIN1+13+17 (with exons 13 and 17). Isoproterenol redistributes BIN1 to t-tubules, recruiting P-RyRs and improving the calcium transient. In cardiac-specific Bin1 heterozygote mice, isoproterenol fails to concentrate BIN1 to t-tubules, impairing P-RyR recruitment. The resultant accumulation of uncoupled P-RyRs increases the incidence of spontaneous calcium release. In human hearts with end-stage ischemic cardiomyopathy, we find that BIN1 is also 50% reduced, with diminished P-RyR association with BIN1.

CONCLUSIONS

On β-AR activation, reorganization of BIN1-induced microdomains recruits P-RyR into dyads, increasing the calcium transient while preserving electric stability. When BIN1 is reduced as in human acquired heart failure, acute stress impairs microdomain formation, limiting contractility and promoting arrhythmias.

Trial watch: IDO inhibitors in cancer therapy

Indoleamine 2,3-dioxigenase 1 (IDO1) is the main enzyme that catalyzes the first, rate-limiting step of the so-called "kynurenine pathway", i.e., the metabolic cascade that converts the essential amino acid L-tryptophan (Trp) into L-kynurenine (Kyn). IDO1, which is expressed constitutively by some tissues and in an inducible manner by specific subsets of antigen-presenting cells, has been shown to play a role in the establishment and maintenance of peripheral tolerance. At least in part, this reflects the capacity of IDO1 to restrict the microenvironmental availability of Trp and to favor the accumulation of Kyn and some of its derivatives. Also, several neoplastic lesions express IDO1, providing them with a means to evade anticancer immunosurveillance. This consideration has driven the development of several IDO1 inhibitors, some of which (including 1-methyltryptophan) have nowadays entered clinical evaluation. In animal tumor models, the inhibition of IDO1 by chemical or genetic interventions is indeed associated with the (re)activation of therapeutically relevant anticancer immune responses. This said, several immunotherapeutic regimens exert robust clinical activity in spite of their ability to promote the expression of IDO1. Moreover, 1-methyltryptophan has recently been shown to exert IDO1-independent immunostimulatory effects. Here, we summarize the preclinical and clinical studies testing the antineoplastic activity of IDO1-targeting interventions.

Regulation of E2F1-induced apoptosis by poly(ADP-ribosyl)ation

The transcription factor adenovirus E2 promoter-binding factor (E2F)-1 normally enhances cell-cycle progression, but it also induces apoptosis under certain conditions, including DNA damage and serum deprivation. Although DNA damage facilitates the phosphorylation and stabilization of E2F1 to trigger apoptosis, how serum starvation renders cells vulnerable to E2F1-induced apoptosis remains unclear. Because poly(ADP-ribose) polymerase 1 (PARP1), a nuclear enzyme essential for genomic stability and chromatin remodeling, interacts directly with E2F1, we investigated the effects of PARP1 on E2F1-mediated functions in the presence and absence of serum. PARP1 attenuation, which increased E2F1 transactivation, induced G2/M cell-cycle arrest under normal growth conditions, but enhanced E2F1-induced apoptosis in serum-starved cells. Interestingly, basal PARP1 activity was sufficient to modify E2F1 by poly(ADP-ribosyl)ation, which stabilized the interaction between E2F1 and the BIN1 tumor suppressor in the nucleus. Accordingly, BIN1 acted as an RB1-independent E2F1 corepressor. Because E2F1 directly activates the BIN1 gene promoter, BIN1 curbed E2F1 activity through a negative-feedback mechanism. Conversely, when the BIN1-E2F1 interaction was abolished by PARP1 suppression, E2F1 continuously increased BIN1 levels. This is functionally germane, as PARP1-depletion-associated G2/M arrest was reversed by the transfection of BIN1 siRNA. Moreover, PARP-inhibitor-associated anti-transformation activity was compromised by the coexpression of dominant-negative BIN1. Because serum starvation massively reduced the E2F1 poly(ADP-ribosyl)ation, we conclude that the release of BIN1 from hypo-poly(ADP-ribosyl)ated E2F1 is a mechanism by which serum starvation promotes E2F1-induced apoptosis.

Cardiac BIN1 folds T-tubule membrane, controlling ion flux and limiting arrhythmia

Cardiomyocyte T tubules are important for regulating ion flux. Bridging integrator 1 (BIN1) is a T-tubule protein associated with calcium channel trafficking that is downregulated in failing hearts. Here we find that cardiac T tubules normally contain dense protective inner membrane folds that are formed by a cardiac isoform of BIN1. In mice with cardiac Bin1 deletion, T-tubule folding is decreased, which does not change overall cardiomyocyte morphology but leads to free diffusion of local extracellular calcium and potassium ions, prolonging action-potential duration and increasing susceptibility to ventricular arrhythmias. We also found that T-tubule inner folds are rescued by expression of the BIN1 isoform BIN1+13+17, which promotes N-WASP-dependent actin polymerization to stabilize the T-tubule membrane at cardiac Z discs. BIN1+13+17 recruits actin to fold the T-tubule membrane, creating a 'fuzzy space' that protectively restricts ion flux. When the amount of the BIN1+13+17 isoform is decreased, as occurs in acquired cardiomyopathy, T-tubule morphology is altered, and arrhythmia can result.

Epigenetic inactivation of the tumor suppressor BIN1 drives proliferation of SNF5-deficient tumors

Emerging evidence demonstrates that subunits of the SWI/SNF chromatin remodeling complex are specifically mutated at high frequency in a variety of human cancer types. SNF5 (SMARCB1/INI1/BAF47), a core subunit of the SWI/SNF complex, is inactivated in the vast majority of rhabdoid tumors (RT), an aggressive type of pediatric cancer. SNF5-deficient cancers are diploid and genomically stable, suggesting that epigenetically based changes in transcription are key drivers of tumor formation caused by SNF5 loss. However, there is limited understanding of the target genes that drive cancer formation following SNF5 loss. Here we performed comparative expression analyses upon three independent SNF5-deficient cancer data sets from both human and mouse and identify downregulation of the BIN1 tumor suppressor as a conserved event in primary SNF5-deficient cancers. We show that SNF5 recruits the SWI/SNF complex to the BIN1 promoter, and that the marked reduction of BIN1 expression in RT correlates with decreased SWI/SNF occupancy. Functionally, we demonstrate that re-expression of BIN1 specifically compromises the proliferation of SNF5-deficient RT cell lines. Identification of BIN1 as a SNF5 target gene reveals a novel tumor suppressive regulatory mechanism whose disruption can drive cancer formation.

Characterization of bridging integrator 1 (BIN1) as a potential tumor suppressor and prognostic marker in hepatocellular carcinoma

It has been shown that bridging integrator 1 (BIN1) can interact with c-myelocytomatosis (c-Myc) oncoprotein in cancer. However, the role of BIN1 in hepatocellular carcinoma (HCC) is not clear. In the present study, we investigated the expression and prognostic role of BIN1 in primary HCC and evaluated the function of BIN1 in hepatocarcinogenesis. Using real-time polymerase chain reaction and Western blot analysis, we found significantly decreased expression of BIN1 in primary HCC tumor tissues (n = 42) compared with adjacent normal tissues and in HCC cell lines. Immunohistochemistry analysis also found decreased BIN1 expression in HCC tumor tissues (n = 117). In clinicopathological analysis, loss of BIN1 expression correlated significantly (P < 0.05) with differentiation scores and tumor size. Importantly, decreased expression of BIN1 in tumors was found to be closely associated with a poor prognosis, and we conclude that BIN1 was an independent prognostic factor in a multivariate analysis. In mechanistic studies, restoring BIN1 expression in BIN1-null HCC cells significantly inhibited cell proliferation and colony formation and induced apoptosis of HCC cells. Furthermore, we found that BIN1 overexpression could significantly suppress the motility and invasion of HCC cells in vitro. Our results indicate that BIN1 may function as a potential tumor suppressor and serve as a novel prognostic marker in HCC patients. The BIN1 molecule might play an important role in tumor growth, cell motility and invasion. Modulation of BIN1 expression may lead to clinical applications of this critical molecule in the control of hepatocellular carcinoma as well as in early and effective diagnosis of this aggressive tumor.

c-MYC suppresses BIN1 to release poly(ADP-ribose) polymerase 1: a mechanism by which cancer cells acquire cisplatin resistance

Cancer cells acquire resistance to DNA-damaging therapeutic agents, such as cisplatin, but the genetic mechanisms through which this occurs remain unclear. We show that the c-MYC oncoprotein increases cisplatin resistance by decreasing production of the c-MYC inhibitor BIN1 (bridging integrator 1). The sensitivity of cancer cells to cisplatin depended on BIN1 abundance, regardless of the p53 gene status. BIN1 bound to the automodification domain of and suppressed the catalytic activity of poly(ADP-ribose) polymerase 1 (PARP1, EC 2.4.2.30), an enzyme essential for DNA repair, thereby reducing the stability of the genome. The inhibition of PARP1 activity was sufficient for BIN1 to suppress c-MYC-mediated transactivation, the G(2)-M transition, and cisplatin resistance. Conversely, overexpressed c-MYC repressed BIN1 expression by blocking its activation by the MYC-interacting zinc finger transcription factor 1 (MIZ1) and thereby released PARP1 activity. Thus, a c-MYC-mediated positive feedback loop may contribute to cancer cell resistance to cisplatin.

Non-hematopoietic expression of IDO is integrally required for inflammatory tumor promotion

Indoleamine 2,3-dioxygenase (IDO) is generally considered to be immunosuppressive but recent findings suggest this characterization oversimplifies its role in disease pathogenesis. Recently, we showed that IDO is essential for tumor outgrowth in the classical two-stage model of inflammatory skin carcinogenesis. Here, we report that IDO loss did not exacerbate classical inflammatory responses. Rather, IDO induction could be elicited by environmental signals and tumor promoters as an integral component of the inflammatory tissue microenvironment even in the absence of cancer. IDO loss had limited impact on tumor outgrowth in carcinogenesis models that lacked an explicit inflammatory tumor promoter. In the context of inflammatory carcinogenesis where IDO was critical to tumor development, the most important source of IDO was radiation-resistant non-hematopoietic cells, consistent with evidence that loss of the IDO regulatory tumor suppressor gene Bin1 in transformed skin cells facilitates IDO-mediated immune escape by a cell autonomous mechanism. Taken together, our results identify IDO as an integral component of 'cancer-associated' inflammation that tilts the immune system toward tumor support. More generally, they promote the concept that mediators of immune escape and cancer-associated inflammation may be genetically synonymous.

Bin1 is linked to metastatic potential and chemosensitivity in neuroblastoma

BACKGROUND

Neuroblastoma (NB) is the most common extracranial solid tumor in children. At the time of diagnosis, the tumor has metastasized in as many as 7 of 10 cases, and survival in high-risk patients remains poor. Accurate classification of high-risk patients is very important since this determines treatment plan, and although a consensus risk classification system has been established for NB, it contains few specific molecular markers that account for aggressive nature and metastatic potential of the tumor. Bin1 expression is reduced in breast, NB, and other cancer types and the reduction correlates with high-risk clinical features. Here we hypothesize that Bin1 has an inhibitory role in metastasis, and therefore decrease in its expression may be a marker of high-risk NB.

PROCEDURE

Initially, breast cancer and NB cell lines derived from metastasis were examined for Bin1 expression. Then, a stable Bin1-overexpressing NB cell line was created and evaluated for in vitro metastatic behaviors using anoikis, invasion, and migration assays, and chemoresponsiveness using MTT assay.

RESULTS

Reduced Bin1 was detected in all cancer cell lines examined, and forced Bin1 overexpression increased NB cell anoikis and enhanced the cell killing by doxorubicin. However, Bin1 overexpression did not significantly affect cell invasion, motility, or proliferation.

CONCLUSIONS

Bin1 appears to function as a metastasis suppressor and chemosensitizer in NB, and resistance to anoikis may be an important metastatic mechanism. Thus, Bin1 expression status could serve as a marker for metastatic potential and chemosensitivity thereby allowing for more accurate classifications of high-risk NB patients.

Bin1 SRC homology 3 domain acts as a scaffold for myofiber sarcomere assembly

In skeletal muscle development, the genes and regulatory factors that govern the specification of myocytes are well described. Despite this knowledge, the mechanisms that regulate the coordinated assembly of myofiber proteins into the functional contractile unit or sarcomere remain undefined. Here we explored the hypothesis that modular domain proteins such as Bin1 coordinate protein interactions to promote sarcomere formation. We demonstrate that Bin1 facilitates sarcomere organization through protein-protein interactions as mediated by the Src homology 3 (SH3) domain. We observed a profound disorder in myofiber size and structural organization in a murine model expressing the Bin1 SH3 region. In addition, satellite cell-derived myogenesis was limited despite the accumulation of skeletal muscle-specific proteins. Our experiments revealed that the Bin1 SH3 domain formed transient protein complexes with both actin and myosin filaments and the pro-myogenic kinase Cdk5. Bin1 also associated with a Cdk5 phosphorylation domain of titin. Collectively, these observations suggest that Bin1 displays protein scaffold-like properties and binds with sarcomeric factors important in directing sarcomere protein assembly and myofiber maturation.

The c-MYC-interacting proapoptotic tumor suppressor BIN1 is a transcriptional target for E2F1 in response to DNA damage

The E2F1 transcription factor, which was originally identified as a cell-cycle initiator, mediates apoptosis in response to DNA damage. As E2F1-induced apoptosis is an attractive mechanism for cancer therapy, it is critical to fully elucidate its effector pathways. Here, we show that the c-MYC-interacting proapoptotic tumor suppressor, BIN1, is transcriptionally activated by E2F1 and mediates E2F1-induced apoptosis in response to DNA damage. Acting through the DNA-binding and transactivation domains, ectopically expressed E2F1 activated the human BIN1 promoter, which contains canonical E2F-recognition sites. Conversely, depletion of E2F1 by small interfering RNA or germline deletion led to BIN1 deficiency. DNA-damaging agents (which included etoposide) increased BIN1 levels, unless E2F1 was deficient. Moreover, endogenous E2F1 protein interacted directly with the BIN1 gene promoter in chromatin, particularly after etoposide treatment. Notably, suppression of BIN1 expression using an antisense (AS) technique attenuated the cell death mediated by E2F1 and etoposide. Although the p53 tumor suppressor, its sibling protein p73, and caspases are well-known E2F1 effectors for DNA damage-induced apoptosis, AS-BIN1 did not compromise their apoptotic functions. Our results collectively suggest that BIN1 is a novel transcriptional target of E2F1 that triggers a unique mode of cell death in response to DNA damage.

Endocytic proteins in the regulation of nuclear signaling, transcription and tumorigenesis

Accumulating evidence argues that many proteins governing membrane sorting during endocytosis participate also in nuclear signaling and transcriptional regulation, mostly by modulating the activity of various nuclear factors. Some adaptors and accessory proteins acting in clathrin-mediated internalization, as well as endosomal sorting proteins can undergo nuclear translocation and affect gene expression directly, while for others the effects may be more indirect. Although it is often unclear to what extent the endocytic and nuclear functions are interrelated, several of such proteins are implicated in the regulation of cell proliferation and tumorigenesis, arguing that their dual-function nature may be of physiological importance.

Inhibitors of indoleamine-2,3-dioxygenase for cancer therapy: can we see the wood for the trees?

Indoleamine-2,3-dioxygenase (IDO) is an immunosuppressive enzyme capable of inhibiting a destructive maternal T cell response against allogeneic fetuses. Expression of IDO is evident in tumours and is thought to enable escape from immunologically mediated rejection. Consequently, clinical trials using an inhibitor of IDO, 1-methyltryptophan (1MT), have been initiated. However, a review of the current literature indicates that we are far from understanding the biological relevance of IDO expression during tumorigenesis. A better understanding of IDO biology is needed to comprehend the effect of IDO inhibitors and to provide a rationale for their therapeutic application in cancer.

Mammary involution and breast cancer risk: transgenic models and clinical studies

Postlactational involution is the process following weaning during which the mammary gland undergoes massive cell death and tissue remodeling as it returns to the pre-pregnant state. Lobular involution is the process by which the breast epithelial tissue is gradually lost with aging of the mammary gland. While postlactational involution and lobular involution are distinct processes, recent studies have indicated that both are related to breast cancer development. Experiments using a variety of rodent models, as well as observations in human populations, suggest that deregulation of postlactational involution may act to facilitate tumor formation. By contrast, new human studies show that completion of lobular involution protects against subsequent breast cancer incidence.

Identification of tyrosine kinase, HCK, and tumor suppressor, BIN1, as potential mediators of AHI-1 oncogene in primary and transformed CTCL cells

AHI-1 is an oncogene often targeted by provirus insertional mutagenesis in murine leukemias and lymphomas. Aberrant expression of human AHI-1 occurs in cutaneous T-cell lymphoma (CTCL) cells and in CD4+CD7− Sezary cells from patients with Sezary syndrome. Stable knockdown of AHI-1 using retroviral-mediated RNA interference in CTCL cells inhibits their transforming activity in vitro and in vivo. To identify genes involved in AHI-1–mediated transformation, microarray analysis was performed to identify differentially expressed genes in AHI-1–suppressed CTCL cells. Fifteen up-regulated and 6 down-regulated genes were identified and confirmed by quantitative reverse transcription-polymerase chain reaction. Seven were further confirmed in a microarray analysis of CD4+CD7− Sezary cells from Sezary syndrome patients. HCK and BIN1 emerged as new candidate cooperative genes, with differential protein expression, which correlates with observed transcript changes. Interestingly, changes in HCK phosphorylation and biologic response to its inhibitor, dasatinib, were observed in AHI-1–suppressed or –overexpressed cells. The tumor suppressor BIN1 physically interacts with MYC in CTCL cells, which also exhibit differential MYC protein expression. In addition, aberrant expression of alternative splicing forms of BIN1 was observed in primary and transformed CTCL cells. These findings indicate that HCK and BIN1 may play critical roles in AHI-1–mediated leukemic transformation of human CTCL cells.

BAR the door: cancer suppression by amphiphysin-like genes

The evolutionarily conserved amphiphysin-like genes Bin1 and Bin3 function in membrane and actin dynamics, cell polarity, and stress signaling. Recent genetic studies in mice discriminate non-essential roles in endocytic processes commonly ascribed to amphiphysins from essential roles in cancer suppression. Bin1 acts in default pathways of apoptosis and senescence that are triggered by the Myc and Raf oncogenes in primary cells, and Bin1 gene products display a 'moonlighting function' in the nucleus where a variety of other 'endocytic' proteins are also found. Together, genetic investigations in yeast, flies, and mice suggest that amphiphysin-like adapter proteins may suppress cancer by helping integrate cell polarity signals generated by actin and vesicle dynamics with central regulators of cell cycle arrest, apoptosis, and immune surveillance.

Immune escape as a fundamental trait of cancer: focus on IDO

Immune escape is a critical gateway to malignancy. The emergence of this fundamental trait of cancer represents the defeat of immune surveillance, a potent, multi-armed and essential mode of cancer suppression that may influence the ultimate clinical impact of an early stage tumor. Indeed, immune escape may be a central modifier of clinical outcomes, by affecting tumor dormancy versus progression, licensing invasion and metastasis and impacting therapeutic response. Although relatively little studied until recently, immune suppression and escape in tumors are now hot areas with clinical translation of several new therapeutic agents already under way. The interconnections between signaling pathways that control immune escape and those that control proliferation, senescence, apoptosis, metabolic alterations, angiogenesis, invasion and metastasis remain virtually unexplored, offering rich new areas for investigation. Here, an overview of this area is provided with a focus on the tryptophan catabolic enzyme indoleamine 2,3-dioxygenase (IDO) and its recently discovered relative IDO2 that are implicated in suppressing T-cell immunity in normal and pathological settings including cancer. Emerging evidence suggests that during cancer progression activation of the IDO pathway might act as a preferred nodal modifier pathway for immune escape, for example analogous to the PI3K pathway for survival or the VEGF pathway for angiogenesis. Small molecule inhibitors of IDO and IDO2 heighten chemotherapeutic efficacy in mouse models of cancer in a nontoxic fashion and an initial lead compound entered phase I clinical trials in late 2007. New modalities in this area offer promising ways to broaden the combinatorial attack on advanced cancers, where immune escape mechanisms likely provide pivotal support.

Bin1 ablation increases susceptibility to cancer during aging, particularly lung cancer

Age is the major risk factor for cancer, but few genetic pathways that modify cancer incidence during aging have been described. Bin1 is a prototypic member of the BAR adapter gene family that functions in vesicle dynamics and nuclear processes. Bin1 limits oncogenesis and is often attenuated in human cancers, but its role in cancer suppression has yet to be evaluated fully in vivo. In the mouse, homozygous deletion of Bin1 causes developmental lethality, so to assess this role, we examined cancer incidence in mosaic null mice generated by a modified Cre-lox technology. During study of these animals, one notable phenotype was an extended period of female fecundity during aging, with mosaic null animals retaining reproductive capability until the age of 17.3 +/- 1.1 months. Through 1 year of age, cancer incidence was unaffected by Bin1 ablation; however, by 18 to 20 months of age, approximately 50% of mosaic mice presented with lung adenocarcinoma and approximately 10% with hepatocarcinoma. Aging mosaic mice also displayed a higher incidence of inflammation and/or premalignant lesions, especially in the heart and prostate. In mice where colon tumors were initiated by a ras-activating carcinogen, Bin1 ablation facilitated progression to more aggressive invasive status. In cases of human lung and colon cancers, immunohistochemical analyses evidenced frequent attenuation of Bin1 expression, paralleling observations in other solid tumors. Taken together, our findings highlight an important role for Bin1 as a negative modifier of inflammation and cancer susceptibility during aging.