Development of a novel co-culture system using human pancreatic cancer cells and human iPSC-derived stellate cells to mimic the characteristics of pancreatic ductal adenocarcinoma in vitro.

Pancreatic ductal adenocarcinoma (PDAC) is a serious disease with poor prognosis and prone to chemotherapy resistance. It is speculated that the tumor microenvironment (TME) of PDAC contributes to these characteristics. However, the detailed mechanisms of interactions between pancreatic cancer cells and stroma in the TME are unclear. Therefore, the aim of this study was to establish a co-culture system that mimics the TME, using cancer cells derived from PDAC patient specimens and stellate cells from human induced pluripotent stem cells as stromal cells. We succeeded in observing the interaction between cancer cells and stellate cells and reproduced some features of PDAC in vitro using our co-culture systems. In addition, we demonstrated the applicability of our co-culture system for drug treatment in vitro. To conclude, we propose our co-culture system as a novel method to analyze cell-cell interactions, especially in the TME of PDAC.

A Genome-Wide CRISPR Activation Screen Identifies PRRX2 as a Regulator of Enzalutamide Resistance in Prostate Cancer.

Androgen receptor (AR) pathway inhibitors are the mainstay treatment for advanced prostate cancer, but resistance to therapy is common. Here, we used a CRISPR activation screen in metastatic castration-sensitive prostate cancer cells to identify genes that promote resistance to AR inhibitors. Activation of the TGFß target gene paired-related homeobox2 (PRRX2) promoted enzalutamide resistance. PRRX2 expression was the highest in double-negative prostate cancer (DNPC), which lack AR signaling and neuroendocrine differentiation, and a PRRX2-related gene signature identified a subset of patients with DNPC with reduced overall survival. PRRX2-expressing cells showed alterations in the CDK4/6/Rb/E2F and BCL2 pathways. Accordingly, treatment with CDK4/6 and BCL2 inhibitors sensitized PRRX2-expressing, castration-resistant tumors to enzalutamide. Overall, PRRX2 was identified as a driver of enzalutamide resistance. The PRRX2 signature merits investigation as a biomarker of enzalutamide resistance in prostate cancer that could be reversed with CDK4/6 and BCL2 inhibitors. SIGNIFICANCE: PRRX2 mediates enzalutamide resistance via activation of the E2F and BCL2 pathways, which can be targeted with CDK4/6 and BCL2 inhibitors to reverse resistance.

Inflammatory bowel disease induces inflammatory and pre-neoplastic changes in the prostate.

BACKGROUND: Inflammatory bowel disease (IBD) has been implicated as a risk factor for prostate cancer, however, the mechanism of how IBD leads to prostate tumorigenesis is not known. Here, we investigated whether chronic intestinal inflammation leads to pro-inflammatory changes associated with tumorigenesis in the prostate. METHODS: Using clinical samples of men with IBD who underwent prostatectomy, we analyzed whether prostate tumors had differences in lymphocyte infiltrate compared to non-IBD controls. In a mouse model of chemically-induced intestinal inflammation, we investigated whether chronic intestinal inflammation could be transferred to the wild-type mouse prostate. In addition, mouse prostates were evaluated for activation of pro-oncogenic signaling and genomic instability. RESULTS: A higher proportion of men with IBD had T and B lymphocyte infiltration within prostate tumors. Mice with chronic colitis showed significant increases in prostatic CD45 + leukocyte infiltration and elevation of three pro-inflammatory cytokines-TIMP-1, CCL5, and CXCL1 and activation of AKT and NF-kB signaling pathways. Lastly, mice with chronic colitis had greater prostatic oxidative stress/DNA damage, and prostate epithelial cells had undergone cell cycle arrest. CONCLUSIONS: These data suggest chronic intestinal inflammation is associated with an inflammatory-rich, pro-tumorigenic prostatic phenotype which may explain how gut inflammation fosters prostate cancer development in men with IBD.

Activated ALK Cooperates with N-Myc via Wnt/ß-Catenin Signaling to Induce Neuroendocrine Prostate Cancer.

Neuroendocrine prostate cancer (NEPC) is an aggressive subtype of prostate cancer with poor prognosis, and there is a critical need for novel therapeutic approaches. NEPC is associated with molecular perturbation of several pathways, including amplification of MYCN. Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase involved in the pathogenesis of neuroblastoma and other malignancies where it cooperates with N-Myc. We previously identified the first case of ALK F1174C-activating mutation in a patient with de novo NEPC who responded to the ALK inhibitor, alectinib. Here, we show that coactivation of ALK and N-Myc (ALK F1174C/N-Myc) is sufficient to transform mouse prostate basal stem cells into aggressive prostate cancer with neuroendocrine differentiation in a tissue recombination model. A novel gene signature from the ALK F1174C/N-Myc tumors was associated with poor outcome in multiple human prostate cancer datasets. ALK F1174C and ALK F1174C/N-Myc tumors displayed activation of the Wnt/ß-catenin signaling pathway. Chemical and genetic ALK inhibition suppressed Wnt/ß-catenin signaling and tumor growth in vitro in NEPC and neuroblastoma cells. ALK inhibition cooperated with Wnt inhibition to suppress NEPC and neuroblastoma proliferation in vitro and tumor growth and metastasis in vivo. These findings point to a role for ALK signaling in NEPC and the potential of cotargeting the ALK and Wnt/ß-catenin pathways in ALK-driven tumors. Activated ALK and N-Myc are well known drivers in neuroblastoma development, suggesting potential similarities and opportunities to elucidate mechanisms and therapeutic targets in NEPC and vice versa. SIGNIFICANCE: These findings demonstrate that coactivation of ALK and N-Myc induces NEPC by stimulating the Wnt/ß-catenin pathway, which can be targeted therapeutically.

Small-Molecule MYC Inhibitors Suppress Tumor Growth and Enhance Immunotherapy.

Small molecules that directly target MYC and are also well tolerated in vivo will provide invaluable chemical probes and potential anti-cancer therapeutic agents. We developed a series of small-molecule MYC inhibitors that engage MYC inside cells, disrupt MYC/MAX dimers, and impair MYC-driven gene expression. The compounds enhance MYC phosphorylation on threonine-58, consequently increasing proteasome-mediated MYC degradation. The initial lead, MYC inhibitor 361 (MYCi361), suppressed in vivo tumor growth in mice, increased tumor immune cell infiltration, upregulated PD-L1 on tumors, and sensitized tumors to anti-PD1 immunotherapy. However, 361 demonstrated a narrow therapeutic index. An improved analog, MYCi975 showed better tolerability. These findings suggest the potential of small-molecule MYC inhibitors as chemical probes and possible anti-cancer therapeutic agents.

EPHB4 inhibition activates ER stress to promote immunogenic cell death of prostate cancer cells.

The EPHB4 receptor is implicated in the development of several epithelial tumors and is a promising therapeutic target, including in prostate tumors in which EPHB4 is overexpressed and promotes tumorigenicity. Here, we show that high expression of EPHB4 correlated with poor survival in prostate cancer patients and EPHB4 inhibition induced cell death in both hormone sensitive and castration-resistant prostate cancer cells. EPHB4 inhibition reduced expression of the glucose transporter, GLUT3, impaired glucose uptake, and reduced cellular ATP levels. This was associated with the activation of endoplasmic reticulum stress and tumor cell death with features of immunogenic cell death (ICD), including phosphorylation of eIF2α, increased cell surface calreticulin levels, and release of HMGB1 and ATP. The changes in tumor cell metabolism after EPHB4 inhibition were associated with MYC downregulation, likely mediated by the SRC/p38 MAPK/4EBP1 signaling cascade, known to impair cap-dependent translation. Together, our study indicates a role for EPHB4 inhibition in the induction of immunogenic cell death with implication for prostate cancer therapy.

Expression of functional folate receptors in multiple myeloma.

Receptor-targeted delivery of imaging and therapeutic agents has emerged as an attractive strategy to diagnosis and treat many diseases including cancer. One of the most well-studied receptors for targeted therapies is the folate receptor (FR) family. FR-α and FR-ß are present on many cancers with little expression in normal tissues; leading to the testing of at least six folate-targeted drugs in human clinical trials for various cancers. However, the expression of FR in blood cancers has not been fully explored with no reports of FR expression in myelomas. Herein, we report the expression of both FR-α and FR-ß on CD138 + plasma cells isolated from patients with multiple myeloma. In addition, all-trans retinoic acid was shown to increase the levels of FR-α and FR-ß in two myeloma cell lines. Altogether, this data suggests that folate-targeted therapies for the treatment of multiple myeloma warrants further investigation.

Anaplastic Lymphoma Kinase Mutation (ALK F1174C) in Small Cell Carcinoma of the Prostate and Molecular Response to Alectinib.

Purpose: Small cell carcinoma of the prostate (SCCP) is an aggressive disease that can arise de novo or by transdifferentiation from prostate adenocarcinoma. Alterations in anaplastic lymphoma kinase (ALK) gene are involved in neuroblastoma, lung cancer, and other malignancies, but its role in SCCP has not been documented. We describe a patient with refractory de novo SCCP with ALK F1174C-activating mutation who obtained clinical benefit from treatment with ALK inhibitor.Experimental Design: Next-generation sequencing (NGS) was used to analyze primary and circulating tumor DNA (ctDNA). Prostate cancer databases were queried for alterations in ALK gene, mRNA, and its impact in clinical outcomes. In vitro prostate cell line/organoid models were generated by lentiviral-mediated expression of ALK and ALK F1174C and assessed for response to ALK inhibitors crizotinib and alectinib.Results: NGS analysis of the primary tumor and ctDNA of a 39-year-old patient with refractory SSCP identified ALK F1174C mutation. Treatment with second-generation ALK inhibitor alectinib resulted in radiographic stable disease for over 6 months, symptomatic improvement, and significant molecular response as reflected by declining ctDNA allele fraction. Analysis of prostate cancer datasets showed that ALK amplification was associated with poor outcome. In prostate cancer cells and organoids, ALK F1174C expression enhanced growth and induced expression of the neuroendocrine marker neuron-specific enolase. Alectinib was more effective than crizotinib in inhibiting ALK F1174C-expressing cell growth.Conclusions: These findings implicate ALK-activating mutations in SCCP pathogenesis and suggest the therapeutic potential of targeting ALK molecular alterations in some patients with SCCP. Clin Cancer Res; 24(12); 2732-9. ©2018 AACR.

Organoids model distinct Vitamin E effects at different stages of prostate cancer evolution.

Vitamin E increased prostate cancer risk in the Selenium and Vitamin E Cancer Prevention Trial (SELECT) through unknown mechanisms while Selenium showed no efficacy. We determined the effects of the SELECT supplements on benign (primary), premalignant ( RWPE-1) and malignant (LNCaP) prostate epithelial organoids. While the supplements decreased proliferation and induced cell death in cancer organoids, they had no effect on the benign organoids. In contrast, Vitamin E enhanced cell proliferation and survival in the premalignant organoids in a manner that recapitulated the SELECT results. Indeed, while Vitamin E induced a pro-proliferative gene expression signature, Selenium alone or combined with Vitamin E produced an anti-proliferative signature. The premalignant organoids also displayed significant downregulation of glucose transporter and glycolytic gene expression pointing to metabolic alterations. Detached RWPE-1 cells had low ATP levels due to diminished glucose uptake and glycolysis which was rescued by Vitamin E through the activation of fatty acid oxidation (FAO). FAO inhibition abrogated the ATP rescue, diminished survival of the inner matrix detached cells, restoring the normal hollow lumen morphology in Vitamin E treated organoids. Organoid models therefore clarify the paradoxical findings from SELECT and demonstrate that Vitamin E promotes tumorigenesis in the early stages of prostate cancer evolution.

Modeling African American prostate adenocarcinoma by inducing defined genetic alterations in organoids.

Genomic studies are rapidly identifying genetic alterations in human cancer, but functional validation of such alterations has been slow. Here, using human prostate cancer as a model, we have assessed the feasibility of engineering defined genetic alterations in well-known cancer driver genes to transform benign prostate epithelial organoids derived from African American men. Benign human prostate organoids were transduced with lentiviruses expressing MYC, shPTEN, shTP53 and AR, alone and in various combinations, to recapitulate prostate cancer development. Organoids expressing MYC, shPTEN, shTP53 and AR (denoted MPPA); MYC, shPTEN and shTP53 (MPP); or MYC (M) were significantly larger, had higher proliferation rates and demonstrated pathologically transformed morphology compared to organoids transduced with control lentivirus. Alterations in MYC, PTEN and TP53 also affected the rate of organoid basal-to-luminal differentiation in vitro. MPPA and MPP organoids expressed the clinical prostate cancer marker AMACR and developed prostate adenocarcinoma when grafted under the renal capsule in mice. These data indicate that genetic alterations commonly observed in human prostate cancer can be rapidly modeled in human organoid culture. Prostate cancer organoids provide a useful pre-clinical model for the evaluation of new candidate cancer genes, cancer disparities, and potentially for testing of novel therapeutic agents.

The allosteric AKT inhibitor, MK2206, decreases tumor growth and invasion in patient derived xenografts of endometrial cancer.

The purpose of this study was to test the effect of MK2206, an allosteric inhibitor of AKT, on the growth and invasion of patient-derived xenografts (PDX) of endometrial cancer. Three PDX lines, USC1 (uterine serous), EEC2 (endometrioid grade 2) and EEC4 (endometrioid grade 3) of endometrial cancer were grafted under the renal capsule of NSG mice. After 2 weeks of tumor growth the mice were treated with vehicle or 120mg/kg MK2206 twice a week for 3 weeks. Growth of all 3 PDX lines of different type and grade was significantly inhibited in response to MK2206 compared with vehicle control. Histological analysis revealed invasion and spread of EEC2 and EEC4 tumors were significantly decreased with MK2206 treatment. Immunohistochemical analysis showed a decrease in Ki67 in EEC2 upon MK2206 treatment, while USC1 and EEC4 tumors did not show differences in Ki67 levels. PR levels were evident in EEC2 which dramatically increased upon MK2206 treatment. In vitro analysis of EEC4 and AN3CA cells showed a dose-dependent decrease in p(Ser473)-AKT and p(Thr308)-AKT with MK2206. Invasion of EEC4 and AN3CA cells also significantly decreased after 36h and 72h of MK2206 treatment. PDX tumors provide an appropriate model for the testing of compounds that incorporates the heterogeneous nature of endometrial cancer. Further studies to determine efficacy of MK2206 alone or in combination with other compounds can also identify predictors of response to these pathway inhibitors.

Bmi1 marks distinct castration-resistant luminal progenitor cells competent for prostate regeneration and tumour initiation.

Identification of defined cell populations with stem/progenitor properties is key for understanding prostate development and tumorigenesis. Here we show that the polycomb repressor protein Bmi1 marks a population of castration-resistant luminal epithelial cells enriched in the mouse proximal prostate. We employ lineage tracing to show that these castration-resistant Bmi1-expressing cells (or CARBs) are capable of tissue regeneration and self-renewal. Notably, CARBs are distinct from the previously described luminal castration-resistant Nkx3.1-expressing cells (CARNs). CARBs can serve as a prostate cancer cell-of-origin upon Pten deletion, yielding luminal prostate tumours. Clonal analysis using the R26R-confetti allele indicates preferential tumour initiation from CARBs localized to the proximal prostate. These studies identify Bmi1 as a marker for a distinct population of castration-resistant luminal epithelial cells enriched in the proximal prostate that can serve as a cell of origin for prostate cancer.

Establishment of human patient-derived endometrial cancer xenografts in NOD scid gamma mice for the study of invasion and metastasis.

OBJECTIVE: Most endometrial cancers are detected early and have a good prognosis, while some endometrial cancers are highly invasive, metastasize early, and respond suboptimally to therapy. Currently, appropriate model systems to study the aggressive nature of these tumors are lacking. The objective of this study was to establish a mouse xenograft model of endometrial tumors derived from patients in order to study the biological aggressive characteristics that underlie invasion and metastasis. METHODS: Endometrial tumor tissue fragments (1.5 mm × 1.5 mm) from patients undergoing surgery, were transplanted under the renal capsule of NOD scid gamma mice. After 6-8 weeks, tumors were excised and serially transplanted into additional mice for propagation. Immunohistochemical analysis of the tumors was done for various tumor markers. RESULTS: Four cases of different subtypes of endometrial cancer were grown and propagated in mice. Three of the four tumor cases invaded into the kidneys and to adjacent organs. While all tumors exhibited minimal to no staining for estrogen receptor α, progesterone receptor staining was observed for tumor grafts. In addition, levels and localization of E-cadherin, cytokeratin and vimentin varied depending on subtype. Finally, all tumor xenografts stained positively for urokinase plasminogen activator while 3 tumor xenografts, which showed invasive characteristics, stained positively for urokinase plasminogen activator receptor. CONCLUSION: Endometrial tumors transplanted under the renal capsule exhibit growth, invasion and local spread. These tumors can be propagated and used to study aggressive endometrial cancer.

Increased AKT or MEK1/2 activity influences progesterone receptor levels and localization in endometriosis.

CONTEXT: Endometriosis is characterized by progesterone resistance and hyperactivity of the AKT and MAPK pathways. Kinases can cause posttranslational modifications of the progesterone receptor (PR) to influence cellular localization and protein stability. OBJECTIVE: The objective of this study was to determine whether the increased AKT or MAPK kinase-1/2 (MEK1/2) activity observed in endometriotic stromal cells (OSIS) from ovarian endometriomas influences levels of PR protein. In turn, the effects of inhibiting AKT or MEK1/2 in the presence of the progestin R5020 on cell viability were investigated. RESULTS: Inhibiting AKT with MK-2206 or MEK1/2 with U0126 for 24 hours in the absence of R5020 increased total and nuclear PRA and PRB protein levels in OSIS but not in eutopic endometrial stromal cells from disease-free patients from disease-free patients. MK-2206 and R5020 decreased OSIS viability and increased apoptosis. Trends toward decreased volumes of sc grafted endometriosis tissues were demonstrated with MK-2206 and progesterone. CONCLUSIONS: Inhibition of AKT or MEK1/2 increased total and nuclear PR protein in OSIS. MK-2206 and R5020 decreased OSIS viability and increased apoptosis. The AKT and MAPK pathways may be potential molecular targets for the treatment of endometriosis.

Diethylstilbestrol induces vaginal adenosis by disrupting SMAD/RUNX1-mediated cell fate decision in the Müllerian duct epithelium.

Women exposed to diethylstilbestrol (DES) in utero frequently develop vaginal adenosis, from which clear cell adenocarcinoma can arise. Despite decades of extensive investigation, the molecular pathogenesis of DES-associated vaginal adenosis remains elusive. Here we report that DES induces vaginal adenosis by inhibiting the BMP4/Activin A-regulated vaginal cell fate decision through a downregulation of RUNX1. BMP4 and Activin A produced by vaginal mesenchyme synergistically activated the expression of ΔNp63, thus deciding vaginal epithelial cell fate in the Müllerian duct epithelial cells (MDECs) via direct binding of SMADs on the highly conserved 5' sequence of ΔNp63. Therefore, mice in which Smad4 was deleted in MDECs failed to express ΔNp63 in vaginal epithelium and developed adenosis. This SMAD-dependent ΔNp63 activation required RUNX1, a binding partner of SMADs. Conditional deletion of Runx1 in the MDECs induced adenosis in the cranial portion of vagina, which mimicked the effect of developmental DES-exposure. Furthermore, neonatal DES exposure downregulated RUNX1 in the fornix of the vagina, where DES-associated adenosis is frequently found. This observation strongly suggests that the downregulation of RUNX1 is the cause of vaginal adenosis. However, once cell fate was determined, the BMP/Activin-SMAD/RUNX1 signaling pathway became dispensable for the maintenance of ΔNp63 expression in vaginal epithelium. Instead, the activity of the ΔNp63 locus in vaginal epithelium was maintained by a ΔNp63-dependent mechanism. This is the first demonstration of a molecular mechanism through which developmental chemical exposure causes precancerous lesions by altering cell fate.

The development of cervical and vaginal adenosis as a result of diethylstilbestrol exposure in utero.

Exposure to exogenous hormones during development can result in permanent health problems. In utero exposure to diethylstilbestrol (DES) is probably the most well documented case in human history. DES, an orally active synthetic estrogen, was believed to prevent adverse pregnancy outcome and thus was routinely given to selected pregnant women from the 1940s to the 1960s. It has been estimated that 5 million pregnant women worldwide were prescribed DES during this period. In the early 1970s, vaginal clear cell adenocarcinomas (CCACs) were diagnosed in daughters whose mother took DES during pregnancy (known as DES daughters). Follow-up studies demonstrated that exposure to DES in utero causes a spectrum of congenital anomalies in female reproductive tracts and CCACs. Among those, cervical and vaginal adenoses are most commonly found, which are believed to be the precursors of CCACs. Transformation related protein 63 (TRP63/p63) marks the cell fate decision of Müllerian duct epithelium (MDE) to become squamous epithelium in the cervix and vagina. DES disrupts the TRP63 expression in mice and induces adenosis lesions in the cervix and vagina. This review describes mouse models that can be used to study the development of DES-induced anomalies, focusing on cervical and vaginal adenoses, and discusses their molecular pathogenesis.

Role of stem cells in human uterine leiomyoma growth.

BACKGROUND: Uterine leiomyoma is the most common benign tumor in reproductive-age women. Each leiomyoma is thought to be a benign monoclonal tumor arising from a single transformed myometrial smooth muscle cell; however, it is not known what leiomyoma cell type is responsible for tumor growth. Thus, we tested the hypothesis that a distinct stem/reservoir cell-enriched population, designated as the leiomyoma-derived side population (LMSP), is responsible for cell proliferation and tumor growth. PRINCIPAL FINDINGS: LMSP comprised approximately 1% of all leiomyoma and 2% of all myometrium-derived cells. All LMSP and leiomyoma-derived main population (LMMP) but none of the side or main population cells isolated from adjacent myometrium carried a mediator complex subunit 12 mutation, a genetic marker of neoplastic transformation. Messenger RNA levels for estrogen receptor-α, progesterone receptor and smooth muscle cell markers were barely detectable and significantly lower in the LMSP compared with the LMMP. LMSP alone did not attach or survive in monolayer culture in the presence or absence of estradiol and progestin, whereas LMMP readily grew under these conditions. LMSP did attach and survive when directly mixed with unsorted myometrial cells in monolayer culture. After resorting and reculturing, LMSP gained full potential of proliferation. Intriguingly, xenografts comprised of LMSP and unsorted myometrial smooth muscle cells grew into relatively large tumors (3.67 ± 1.07 mm(3)), whereas xenografts comprised of LMMP and unsorted myometrial smooth muscle cells produced smaller tumors (0.54 ± 0.20 mm(3), p<0.05, n = 10 paired patient samples). LMSP xenografts displayed significantly higher proliferative activity compared with LMMP xenografts (p<0.05). CONCLUSIONS: Our data suggest that LMSP, which have stem/reservoir cell characteristics, are necessary for in vivo growth of leiomyoma xenograft tumors. Lower estrogen and progesterone receptor levels in LMSP suggests an indirect paracrine effect of steroid hormones on stem cells via the mature neighboring cells.

Identification of a novel microRNA cluster miR-193b-365 in multiple myeloma.

There is accumulating evidence that the patterns of altered expression of microRNAs (miRNAs) correlate with distinct types of hematological malignancies. There is also emerging evidence for such miRNAs expression in multiple myeloma (MM), but the identity of the miRNAs that are abnormally expressed in this disease has not been elucidated. In the current study, we examined the miRNAs perturbed in CD138 positive MM cell lines and CD138 positive primary MM cells, using microarray analysis and quantitative real-time PCR. The expression levels in these cells were compared with the expression levels in CD138 positive plasma cells isolated from bone marrows of healthy donors. Our data demonstrate that multiple new miRNAs are commonly up-regulated and down-regulated including a new miRNA cluster, miR-193b-365, composed of two paralogs that were significantly up-regulated in MM. The organization and the sequences of the new miR-193b-365 cluster are highly conserved among vertebrates. Given that dysregulation of miR-193b-365 cluster has not been identified in other hematological malignancies examined to date, our findings suggest that miR-193b-365 cluster is part of the unique miRNA signature in MM.

Functional involvement of human discs large tumor suppressor in cytokinesis.

Cytokinesis is the final step of cell division that completes the separation of two daughter cells. We found that the human discs large (hDlg) tumor suppressor homologue is functionally involved in cytokinesis. The guanylate kinase (GUK) domain of hDlg mediates the localization of hDlg to the midbody during cytokinesis, and over-expression of the GUK domain in U2OS and HeLa cells impaired cytokinesis. Mouse embryonic fibroblasts (MEFs) derived from dlg mutant mice contained an increased number of multinucleated cells and showed reduced proliferation in culture. A kinesin-like motor protein, GAKIN, which binds directly to the GUK domain of hDlg, exhibited a similar intracellular distribution pattern with hDlg throughout mitosis and localized to the midbody during cytokinesis. However, the targeting of hDlg and GAKIN to the midbody appeared to be independent of each other. The midbody localization of GAKIN required its functional kinesin-motor domain. Treatment of cells with the siRNA specific for hDlg and GAKIN caused formation of multinucleated cells and delayed cytokinesis. Together, these results suggest that hDlg and GAKIN play functional roles in the maintenance of midbody architecture during cytokinesis.