Hepatoma Up-regulated Protein Research Articles

HURP facilitates spindle assembly by stabilizing microtubules and working synergistically with TPX2

In vertebrate spindles, most microtubules are formed via branching microtubule nucleation, whereby microtubules nucleate along the side of pre-existing microtubules. Hepatoma up-regulated protein (HURP) is a microtubule-associated protein that has been implicated in spindle assembly, but its mode of action is yet to be defined. In this study, we show that HURP is necessary for RanGTP-induced branching microtubule nucleation in Xenopus egg extract. Specifically, HURP stabilizes the microtubule lattice to promote microtubule formation from γ-TuRC. This function is shifted to promote branching microtubule nucleation through enhanced localization to TPX2 condensates, which form the core of the branch site on microtubules. Lastly, we provide a high-resolution cryo-EM structure of HURP on the microtubule, revealing how HURP binding stabilizes the microtubule lattice. We propose a model in which HURP stabilizes microtubules during their formation, and TPX2 preferentially enriches HURP to microtubules to promote branching microtubule nucleation and thus spindle assembly.

HURP regulates Kif18A recruitment and activity to synergistically control microtubule dynamics

During mitosis, microtubule dynamics are regulated to ensure proper alignment and segregation of chromosomes. The dynamics of kinetochore-attached microtubules are regulated by hepatoma-upregulated protein (HURP) and the mitotic kinesin-8 Kif18A, but the underlying mechanism remains elusive. Using single-molecule imaging in vitro, we demonstrate that Kif18A motility is regulated by HURP. While sparse decoration of HURP activates the motor, higher concentrations hinder processive motility. To shed light on this behavior, we determine the binding mode of HURP to microtubules using cryo-EM. The structure helps rationalize why HURP functions as a microtubule stabilizer. Additionally, HURP partially overlaps with the microtubule-binding site of the Kif18A motor domain, indicating that excess HURP inhibits Kif18A motility by steric exclusion. We also observe that HURP and Kif18A function together to suppress dynamics of the microtubule plus-end, providing a mechanistic basis for how they collectively serve in microtubule length control.

HURP binding to the vinca domain of β-tubulin accounts for cancer drug resistance

Vinca alkaloids, a class of tubulin-binding agent, are widely used in treating cancer, yet the emerging resistance compromises their efficacy. Hepatoma up-regulated protein (HURP), a microtubule-associated protein displaying heightened expression across various cancer types, reduces cancer cells’ sensitivity to vinca-alkaloid drugs upon overexpression. However, the molecular basis behind this drug resistance remains unknown. Here we discover a tubulin-binding domain within HURP, and establish its role in regulating microtubule growth. Cryo-EM analysis reveals interactions between HURP’s tubulin-binding domain and the vinca domain on β-tubulin -- the site targeted by vinca alkaloid drugs. Importantly, HURP competes directly with vinorelbine, a vinca alkaloid-based chemotherapeutic agent, countering microtubule growth defects caused by vinorelbine both in vitro and in vivo. Our findings elucidate a mechanism driving drug resistance in HURP-overexpressing cancer cells and emphasize HURP tubulin-binding domain’s role in mitotic spindle assembly. This underscores its potential as a therapeutic target to improve cancer treatment.

Molecular interplay between HURP and Kif18A in mitotic spindle regulation.

During mitosis, microtubule dynamics are regulated to ensure proper alignment and segregation of chromosomes. The dynamics of kinetochore-attached microtubules are regulated by hepatoma-upregulated protein (HURP) and the mitotic kinesin-8 Kif18A, but the underlying mechanism remains elusive. Using single-molecule imaging in vitro, we demonstrate that Kif18A motility is regulated by HURP. While sparse decoration of HURP activates the motor, higher concentrations hinder processive motility. To shed light on this behavior, we determined the binding mode of HURP to microtubules using Cryo-EM. The structure reveals that one HURP motif spans laterally across β-tubulin, while a second motif binds between adjacent protofilaments. HURP partially overlaps with the microtubule-binding site of the Kif18A motor domain, indicating that excess HURP inhibits Kif18A motility by steric exclusion. We also observed that HURP and Kif18A function together to suppress dynamics of the microtubule plus-end, providing a mechanistic basis for how they collectively serve in spindle length control.

Statement of Retraction: MicroRNA-4521 targets hepatoma up-regulated protein (HURP) to inhibit the malignant progression of breast cancer

Statement of Retraction: MicroRNA-4521 targets hepatoma up-regulated protein (HURP) to inhibit the malignant progression of breast cancer

Large‐scale phosphomimetic screening identifies phospho‐modulated motif‐based protein interactions

Phosphorylation is a ubiquitous post‐translation modification that regulates protein function by promoting, inhibiting or modulating protein–protein interactions. Hundreds of thousands of phosphosites have been identified but the vast majority have not been functionally characterised and it remains a challenge to decipher phosphorylation events modulating interactions. We generated a phosphomimetic proteomic peptide‐phage display library to screen for phosphosites that modulate short linear motif‐based interactions. The peptidome covers ~13,500 phospho‐serine/threonine sites found in the intrinsically disordered regions of the human proteome. Each phosphosite is represented as wild‐type and phosphomimetic variant. We screened 71 protein domains to identify 248 phosphosites that modulate motif‐mediated interactions. Affinity measurements confirmed the phospho‐modulation of 14 out of 18 tested interactions. We performed a detailed follow‐up on a phospho‐dependent interaction between clathrin and the mitotic spindle protein hepatoma‐upregulated protein (HURP), demonstrating the essentiality of the phospho‐dependency to the mitotic function of HURP. Structural characterisation of the clathrin‐HURP complex elucidated the molecular basis for the phospho‐dependency. Our work showcases the power of phosphomimetic ProP‐PD to discover novel phospho‐modulated interactions required for cellular function.

MicroRNA-4521 targets hepatoma up-regulated protein (HURP) to inhibit the malignant progression of breast cancer

ABSTRACT Breast cancer (BC) is a common malignancy among women, and microRNAs (miRNAs) play a role in its progression. Reportedly, microRNA-4521 (miR-4521) participates in regulating the progression of some carcinomas. In the present work, miR-4521 and hepatoma up-regulated protein (HURP) mRNA expressions in BC tissues and cell lines were examined by qRT-PCR. After miR-4521 was overexpressed or knocked down in BC cells, CCK-8 experiment and EdU experiment were employed to detect BC cell growth. Moreover, the Transwell assay was adopted to detect the migration and invasion. Subsequently, flow cytometry was executed to evaluate the changes in cell cycle progression. KEGG analysis was utilized to predict the signaling pathways related with the target genes of miR-524-5p. The binding relationship between miR-4521 and HURP 3ʹUTR was validated by dual-luciferase reporter gene experiment. HURP and NF-kB p65 protein expression in BC cells was detected by Western blot. It was revealed that, miR-4521 was lowly expressed in BC tissues, and its expression was associated with tumor grade, lymph node metastasis and clinical stage of the patients. Overexpression of miR-4521 suppressed the growth, migration, invasion and cell cycle progression of BC cells and restrained p65 expression; downregulation of miR-4521 in BC cells showed opposite biological effects. Additionally, HURP was a downstream target gene of miR-4521, and overexpression of HURP reversed the above effects of miR-4521 overexpression. In short, miR-4521 can inhibit BC progression by modulating the HURP/NF-κB pathway.

Hepatoma upregulated protein and Ki-67 expression in resectable hepatocellular carcinoma.

Hepatoma upregulated protein (HURP) and Ki-67 have been identified as cancer-related genes involved in cell growth and proliferation. Previous experimental studies have suggested an essential role for HURP expression in liver carcinogenesis. However, data regarding HURP expression in hepatocellular carcinoma (HCC) and its correlation with patient outcomes are limited. In this study, we examined the clinicopathologic features associated with HURP expression in HCC, and compared them to the results of the Ki-67 study. Eighty-seven resected HCC at tumor, node, metastasis (TNM) stages I (n = 28), II (n = 29), and III (n = 30) were evaluated. HURP and Ki-67 expression were assessed by immunohistochemistry. Multivariate analysis was used to examine the prognostic significance of HURP and Ki-67 expression. HURP expression in HCC tissue was observed in 59% of patients and associated with female sex, low white blood cell count, and low platelet count. Ki-67 expression was observed in 67% of patients and associated with younger age, higher serum α-fetoprotein (AFP) levels, and frequent microvascular invasion. Univariate analysis showed that factors related to overall survival were: age >55 years, AFP >20 ng/mL, indocyanine green retention rate at 15 minutes (ICG-15) >15%, tumor size >5 cm, multiple tumors, macrovascular invasion, microvascular invasion, Ki-67 expression, and serum vascular endothelial growth factor >170 pg/mL. HURP expression was not associated with postresection survival. Multivariate analysis indicated that macrovascular invasion, multiple tumors, ICG-15 >15%, and Ki-67 expression were independent factors for overall survival. Multiple tumors and Ki-67 expression were independent factors related to recurrence-free survival. In our study, HURP expression in HCC tissue was not associated with post-resection survival. Ki-67 expression was an independent prognostic factor for survival. Our results suggest that the effect of HURP activity on growth, invasion, and postresection outcome of HCC in actual patients is less than previously demonstrated in experimental studies.

The expression of hepatoma upregulated protein in human endometrium during the menstrual cycle

Aims Human endometrium resists embryo implantation except during the window period. Currently, uterine HURP expression is known to be involved in endometrial stromal proliferation during embryo implantation of mice. Thus, we demonstrated hepatoma up-regulated protein (HURP) expression in the human endometrium during the menstrual cycle, as well as HURP regulation in endometrial stromal cells (ESCs). Materials and methods We collected human endometrial samples from different menstrual cycle phases (early/late proliferative, and early/mid/late secretory), and then analyzed these samples by immunohistochemistry, reverse transcription-polymerase chain reaction, and Western blotting. We also assessed the effects of two sex-steroid hormones, 17β-estradiol (E2) and 4-pregnene-3,20-dione (P4) on the cultured stromal cells. Results HURP protein was localized to the nucleus of the endometrial both epithelial and stromal cells in all stages. Also, HURP mRNA and protein in human endometrial tissue was significantly up-regulated during late-proliferative and secretory phase, compared with early-proliferative phase. In ESCs, HURP expression was regulated by E2, but not P4. Conclusions We indicated that cyclic changes in HURP expression in human normal ESC strongly suggested up-regulation by estrogen. Taken together, since estrogen responses are fundamental in endometrial biology, uterine expression of HURP may be involved in female reproductive function during the menstrual cycle.

RanBP1 controls the Ran pathway in mammalian cells through regulation of mitotic RCC1 dynamics

ABSTRACT The Ran GTPase plays critical roles in multiple cellular processes including interphase nucleocytoplasmic transport and mitotic spindle assembly. During mitosis in mammalian cells, GTP-bound Ran (Ran-GTP) is concentrated near mitotic chromatin while GDP-bound Ran (Ran-GDP) is more abundant distal to chromosomes. This pattern spatially controls spindle formation because Ran-GTP locally releases spindle assembly factors (SAFs), such as Hepatoma Up-Regulated Protein (HURP), from inhibitory interactions near chromosomes. Regulator of Chromatin Condensation 1 (RCC1) is Ran’s chromatin-bound exchange factor, and RanBP1 is a conserved Ran-GTP-binding protein that has been implicated as a mitotic regulator of RCC1 in embryonic systems. Here, we show that RanBP1 controls mitotic RCC1 dynamics in human somatic tissue culture cells. In addition, we observed the re-localization of HURP in metaphase cells after RanBP1 degradation, consistent with the idea that altered RCC1 dynamics functionally modulate SAF activities. Together, our findings reveal an important mitotic role for RanBP1 in human somatic cells, controlling the spatial distribution and magnitude of mitotic Ran-GTP production and thereby ensuring the accurate execution of Ran-dependent mitotic events. Abbreviations AID: Auxin-induced degron; FLIP: Fluorescence loss in photobleaching; FRAP: Fluorescence recovery after photobleaching; GDP: guanosine diphosphate; GTP: guanosine triphosphate; HURP: Hepatoma Up-Regulated Protein; NE: nuclear envelope; NEBD: Nuclear Envelope Breakdown; RanBP1: Ran-binding protein 1; RanGAP1: Ran GTPase-Activating Protein 1; RCC1: Regulator of Chromatin Condensation 1; RRR complex: RCC1/Ran/RanBP1 heterotrimeric complex; SAF: Spindle Assembly Factor; TIR1: Transport Inhibitor Response 1 protein; XEE: Xenopus egg extract.

Overexpression of HURP mRNA in head and neck carcinoma and association with in vitro response to vinorelbine.

HURP gene encodes the hepatoma upregulated protein (HURP), a microtubule associated protein regulating mitotic spindle dynamics, which promotes chromosomal congression and alignment during mitosis, with a potential role in tumorigenesis. In the present study, HURP mRNA expression was investigated by reverse transcription-quantitative PCR in oropharyngeal squamous cell carcinoma (OPSCC). Primary OPSCC tumors from 107 patients and 48 adjacent normal tissues, as well as 12 respiratory tract cancer cell lines (9 head and neck squamous cell carcinoma, 2 lung cancer and 1 normal bronchial) were utilised in the present study. mRNA expression levels of HURP were higher in malignant OPSCC tissues compared with in normal mucosa (P<1×10-5) and significantly associated with sex and smoking status (P<0.0001). Vinorelbine in vitro toxicity at half-maximal inhibitory concentration (IC50) was measured in the 11 cancer cell lines using an MTT assay. Sensitivity to vinorelbine was significantly correlated with HURP expression (r=0.636; P=0.035). The data indicated that HURP overexpression is frequent in OPSCC tissues and associated with smoking. The correlation between HURP mRNA expression and vinorelbine in vitro response suggests that HURP is a potential modulator of vinorelbine response; therefore, it should be explored for its possible predictive value for the efficiency of vinorelbine treatment in this type of cancer.

Importin-β/karyopherin-β1 modulates mitotic microtubule function and taxane sensitivity in cancer cells via its nucleoporin-binding region.

The nuclear transport receptor importin-β/karyopherin-β1 is overexpressed in cancers that display genomic instability. It is regarded as a promising cancer target and inhibitors are being developed. In addition to its role in nucleo-cytoplasmic transport, importin-β regulates mitosis, but the programmes and pathways in which it operates are defined only in part. To unravel importin-β's mitotic functions we have developed cell lines expressing either wild-type or a mutant importin-β form in characterised residues required for nucleoporin binding. Both forms similarly disrupted spindle pole organisation, while only wild-type importin-β affected microtubule plus-end function and microtubule stability. A proteome-wide search for differential interactors identified a set of spindle regulators sensitive to mutations in the nucleoporin-binding region. Among those, HURP (hepatoma up-regulated protein) is an importin-β interactor and a microtubule-stabilising factor. We found that induction of wild type, but not mutant importin-β, under the same conditions that destabilise mitotic microtubules, delocalised HURP, indicating that the spatial distribution of HURP along the spindle requires importin-β's nucleoporin-binding residues. Concomitantly, importin-β overexpression sensitises cells to taxanes and synergistically increases mitotic cell death. Thus, the nucleoporin-binding domain is dispensable for importin-β function in spindle pole organisation, but regulates microtubule stability, at least in part via HURP, and renders cells vulnerable to certain microtubule-targeting drugs.

Differential contribution of protein phosphatase 1α to cell transformation of different cell types.

Protein phosphorylation plays roles in cell transformation. Numerous protein kinase enzymes actively participate in the formation of various types of cancer by phosphorylating downstream substrates. Aurora‑A is a widely known Serine/Threonine (Ser/Thr) oncogenic kinase, which is upregulated in more than twenty types of human cancer. This enzyme phosphorylates a wide range of substrates. For example, Aurora‑A induces cell transformation by phosphorylating hepatoma upregulated protein (HURP) at four serine residues, which in turn decreases the phosphorylated levels of cell‑growth suppressive Jun N‑terminal kinase (p‑JNK). Various protein phosphatase enzymes are considered tumor suppressors by the dephosphorylation and consequent inactivation of their oncogenic substrates. Protein phosphatase 1α (PP1α), for instance, acts on Aurora‑A by dephosphorylating its substrates. However, the role of PP1α in cancer progression remains ambiguous. PP1α is overexpressed in several cancer tissues, and induces cell apoptosis and differentiation or it inhibits tumor formation in other types of cells. In addition, positive and negative correlations between PP1α expression and lung cancer development have been documented. These observations suggest the differential regulation of PP1α in various cancer tissues, or propose an ambiguous contribution of PP1α to lung cancer development. In order to investigate these contradictory conclusions, it was reported that the chromosomal region covering the PP1α locus was subjected to DNA alterations, such as gain or loss in various human cancer types by a study based on literature search. Upregulation of PP1α was noted in a collection of lung cancer tissues, and was required for the cell transformation of the lung cancer cell line A549. In contrast to this finding, overexpression of ectopic PP1α inhibited cell proliferation in 293T cells. Mechanistic studies revealed that PP1α activated AKT in A549 cells, whereas it further inactivated AKT and disrupted the HURP/JNK signaling cascade in 293T cells. Collectively, the data indicated that PP1α exerted an oncogenic function in lung cancer, while exhibiting various effects on cell transformation in different types of cells via distinct or opposite mechanisms.

The microtubule-associated protein HURP recruits the centrosomal protein TACC3 to regulate K-fiber formation and support chromosome congression

Kinetochore fibers (K-fibers) are microtubule bundles attached to chromosomes. Efficient K-fiber formation is required for chromosome congression, crucial for faithful chromosome segregation in cells. However, the mechanisms underlying K-fiber formation before chromosome biorientation remain unclear. Depletion of hepatoma up-regulated protein (HURP), a RanGTP-dependent microtubule-associated protein localized on K-fibers, has been shown to result in low-efficiency K-fiber formation. Therefore, here we sought to identify critical interaction partners of HURP that may modulate this function. Using co-immunoprecipitation and bimolecular fluorescence complementation assays, we determined that HURP interacts directly with the centrosomal protein transforming acidic coiled coil-containing protein 3 (TACC3), a centrosomal protein, both in vivo and in vitro through the HURP1-625 region. We found that HURP is important for TACC3 function during kinetochore microtubule assembly at the chromosome region in prometaphase. Moreover, HURP regulates stable lateral kinetochore attachment and chromosome congression in early mitosis by modulation of TACC3. These findings provide new insight into the coordinated regulation of K-fiber formation and chromosome congression in prometaphase by microtubule-associated proteins.

Abstract 4094: Accumulation of hepatoma up-regulated protein in prostate cancer cells inhibits bortezomib-induced apoptosis

Abstract The increased understanding of cellular signaling pathways in the regulation of tumor progression and resistance, together with the identification of key molecular markers has allowed for considerable advances in the establishment of therapies for therapy-resistant Prostate cancer (PCa). Hepatoma Up-Regulated Protein (HURP), is overexpressed in several tumors, and has been identified as a multifunctional protein with tumorigenic capacity. We previously reported on HURP as an essential modulator of PCa resistance to radiation therapy. Bortezomib, a proteasome inhibitor used clinically for multiple myeloma, has been shown to induce apoptosis in PCa cells. In the present study, we evaluate HURP’s role in PCa resistance pathways by analyzing its effects on bortezomib-induced apoptosis. LNCaP-TetOn-HURP, DU145-TetOn-HURP, and PC3-TetOn-HURP clones were established for the expression of HURP. HURP expression was induced with doxycycline (Dox) for 48 h. Next, cells were treated with bortezomib (50 nM) for 24h. To assess the effect of HURP on bortezomib-induced apoptosis, the cells were harvested and subjected to flow cytometry (FC) analysis using annexin V/PI staining. Apoptosis was observed in control cells (-Dox) following the treatment with bortezomib. Induction of HURP expression (+Dox), blocked bortezomib-induced apoptosis. This effect was observed only in LNCaP- and DU145-TetOn-HURP cells with a 1.8 and 2.1 fold decrease in apoptosis, respectively; but not in PC3-TetOn-HURP cells. In addition, we performed FC analysis of DHR123 to analyze the effects of HURP on bortezomib-induced accumulation of reactive oxygen species (ROS). HURP blocked bortezomib-induced ROS accumulation in LNCaP- and DU145-TetOn-HURP cells with a 0.3 and 0.15 fold change, respectively. Bortezomib also induced the expression of p53 and Noxa, and enhanced the cleavage of PARP in LNCaP- and DU145-TetOn-HURP control cells (-Dox), but not in (-Dox) PC3-TetOn-HURP cells. Induction of HURP, however blocked effects on apoptosis effectors in LNCaP- and DU145-TetOn-HURP. Western blot analysis also demonstrated that in HURP-expressing cells, bortezomib-inhibited the phosphorylation of ASK1, JNK or p38. Finally, we assessed the effects of HURP expression on the cytoplasmic localization of Noxa, a mediator of bortezomib-induced apoptotic signaling by immunocytochemistry. Noxa staining was weakly detectable or absent in HURP expressing cells, suggesting the ability of HURP overload to block bortezomib-induced Noxa expression.Overall, our results show that HURP-induced resistance of PCa cells to bortezomib is attributed to the effects of this protein on mechanisms related to a non-specific overload response leading to the activation of ubiquitin system. Funding: PCRP W81XWH-14-1-0151 (CRG), UMMC Department of Pathology (MH) Citation Format: Mohamed Hassan, Abdelouahid Elkhattouti, Nasir Butt, Ingrid Espinoza, Christian Gomez. Accumulation of hepatoma up-regulated protein in prostate cancer cells inhibits bortezomib-induced apoptosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4094. doi:10.1158/1538-7445.AM2017-4094

Gsk3β and Tomm20 are substrates of the SCFFbxo7/PARK15 ubiquitin ligase associated with Parkinson's disease.

Fbxo7 is a clinically relevant F-box protein, associated with both cancer and Parkinson's disease (PD). Additionally, SNPs within FBXO7 are correlated with alterations in red blood cell parameters. Point mutations within FBXO7 map within specific functional domains, including near its F-box domain and its substrate recruiting domains, suggesting that deficiencies in SCFFbxo7/PARK15 ubiquitin ligase activity are mechanistically linked to early-onset PD. To date, relatively few substrates of the ligase have been identified. These include HURP (hepatoma up-regulated protein), whose ubiquitination results in proteasome-mediated degradation, and c-IAP1 (inhibitor of apoptosis protein 1), TNF receptor-associated factor 2 (TRAF2), and NRAGE, which are not destabilized as a result of ubiquitination. None of these substrates have been linked directly to PD, nor has it been determined whether they would directly engage neuronal cell death pathways. To discover ubiquitinated substrates of SCFFbxo7 implicated more directly in PD aetiology, we conducted a high-throughput screen using protein arrays to identify new candidates. A total of 338 new targets were identified and from these we validated glycogen synthase kinase 3β (Gsk3β), which can phosphorylate α-synuclein, and translocase of outer mitochondrial membrane 20 (Tomm20), a mitochondrial translocase that, when ubiquitinated, promotes mitophagy, as SCFFbxo7 substrates both in vitro and in vivo. Ubiquitin chain restriction analyses revealed that Fbxo7 modified Gsk3β using K63 linkages. Our results indicate that Fbxo7 negatively regulates Gsk3β activity, rather than its levels or localization. In addition, Fbxo7 ubiquitinated Tomm20, and its levels correlated with Fbxo7 expression, indicating a stabilizing effect. None of the PD-associated mutations in Fbxo7 impaired Tomm20 ubiquitination. Our findings demonstrate that SCFFbxo7 has an impact directly on two proteins implicated in pathological processes leading to PD.

Abstract 1651: Overexpression of hepatoma upregulated protein (HURP) promotes radioresistance in prostate cancer cells

Abstract Despite progression in diagnosis and treatment, prostate cancer (PCa) still represents major cause of cancer-related mortality and morbidity in men. Although radiation therapy offers clinical benefit over other therapeutic modalities, the success of this therapeutic modality is commonly hampered by significant resistance in advanced tumor. So far, the mechanisms governing the acquired resistance to radiotherapy have not been discussed in detail. Hepatoma Up-Regulated Protein (HURP) is a cell cycle-regulated and microtubule-associated protein. It functions as a Ran GTPase effector and is involved in the stabilization of the mitotic kinetochore fibers. The expression of this protein is elevated in different tumor types and associated with tumor progression and aggressiveness. We recently reported on the value of HURP as an independent prognostic factor for high-risk PCa. The aim of this study was to address the role of HURP in the modulation of PCa resistance to γ- irradiation. Cell lines (LNCaP, PC3, and DU145) with regulated expression of HURP protein using a Lent viral Tet-On 3G Inducible Expression System were irradiated using a Cs-137 γ-source. Overexpression of HURP suppressed γ- irradiation- induced apoptosis. This suppression was associated with the expression of E2F1, p53, p21 together with the phosphorylation of apoptosis signal-regulating kinase1 (ASK1), c-jun-N-terminal kinase (JNK) and Ataxia-telangiectasia mutated (ATM) and histone family member X (H2AX). Also, inhibition of γ- irradiation- induced- cytochrome c release, cleavage of caspase-9, caspase-3, PARP, and reactive oxygen species (ROS) was noted. The observed resistance was consequence of HURP's ability to trigger the ubiquitination of p53 and ATM that, in turn, resulted in the inhibition of downstream pathways, which are essential for the modulation of γ- irradiation-induced apoptosis. Our data provide evidence for the involvement of HURP in the modulation of PCa cell resistance to γ-irradiation via a mechanism mediated by ubiquitination of ATM and p53. Understanding of the biological mechanisms underlying HURP-mediated resistance of PCa to available therapies may help to improve the treatment strategy and emphasize HURP as therapeutic target for PCa treatment. Funding sources: Department of Defense Grant PC094680 and Prostate Cancer Foundation Creativity Award. Citation Format: Mohamed Hassan, Abdelouahid El Khattouti, Tangeng Ma, Ingrid Espinoza, W. Andrew Day, Srinivasan Vijayakumar, Christian R. Gomez. Overexpression of hepatoma upregulated protein (HURP) promotes radioresistance in prostate cancer cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1651.

Hypoxia on the Expression of Hepatoma Upregulated Protein in Prostate Cancer Cells.

Hepatoma upregulated protein (HURP) is a multifunctional protein with clinical promise. This protein has been demonstrated to be a predictive marker for the outcome in high-risk prostate cancer (PCa) patients, besides being a resistance factor in PCa. Although changes in oxygen tension (pO2) are associated with PCa aggressiveness, the role of hypoxia in the regulation of tumor progression genes such as HURP has not yet been described. We hypothesized that pO2 alteration is involved in the regulation of HURP expression in PCa cells. In the present study, PCa cells were incubated at 2% O2 (hypoxia) and 20% O2 (normoxia) conditions. Hypoxia reduced cell growth rate of PCa cells, when compared to the growth rate of cells cultured under normoxia (p < 0.05). The decrease in cell viability was accompanied by fivefold (p < 0.05) elevated rate of vascular endothelial growth factor (VEGF) release. The expression of VEGF and the hypoxia-inducible metabolic enzyme carbonic anhydrase 9 were elevated maximally nearly 61-fold and 200-fold, respectively (p < 0.05). Noted in two cell lines (LNCaP and C4-2B) and independent of the oxygen levels, HURP expression assessed at both mRNA and protein levels was reduced. However, the decrease was more pronounced in cells cultured under hypoxia (p < 0.05). Interestingly, the analysis of patients’ specimens by Western blot revealed a marked increase of HURP protein (fivefold), when compared to control (cystoprostatectomy) tissue (p < 0.05). Immunohistochemistry analysis showed an increase in the immunostaining intensity of HURP and the hypoxia-sensitive molecules, hypoxia-inducible factor 1-alpha (HIF-1α), VEGF, and heat-shock protein 60 (HSP60) in association with tumor grade. The data also suggested a redistribution of subcellular localization for HURP and HIF-1α from the nucleus to the cytoplasmic compartment in relation to increasing tumor grade. Analysis of HURP Promoter for HIF-1-binding sites revealed presence of four putative HIF binding sites on the promoter of DLGAP5/HURP gene in the non-translated region upstream from the start codon, suggesting association between HIF-1α and the regulation of HURP protein. Taken together, our findings suggest a modulatory role of hypoxia on the expression of HURP. Additionally our results provide basis for utilization of tumor-associated molecules as predictors of aggressive PCa.

Inhibition of apoptosis by oncogenic hepatitis B virus X protein: Implications for the treatment of hepatocellular carcinoma.

Hepatitis B virus X protein (HBx) plays an important role in the development of hepatocellular carcinoma (HCC). In addition, hepatoma upregulated protein (HURP) is a cellular oncogene that is upregulated in a majority of HCC cases. We highlight here recent findings demonstrating a link between HBx, HURP and anti-apoptosis effects observed in cisplatin-treated HCC cells. We observed that Hep3B cells overexpressing HBx display increased HURP mRNA and protein levels, and show resistance to cisplatin-induced apoptosis. Knockdown of HURP in HBx-expressing cells reverses this effect, and sensitizes cells to cisplatin. The anti-apoptotic effect of HBx requires activation of the p38/MAPK pathway as well as expression of SATB1, survivin and HURP. Furthermore, silencing of HURP using short-hairpin RNA promotes accumulation of p53 and reduces cell proliferation in SK-Hep-1 cells (p53(+/-)), whereas these effects are not observed in p53-mutant Mahlavu cells. Similarly, HURP silencing does not affect the proliferation of H1299 lung carcinoma cells or Hep3B HCC cells which lack p53. Silencing of HURP sensitizes SK-Hep-1 cells to cisplatin. While HURP overexpression promotes p53 ubiquitination and degradation by the proteasome, HURP silencing reverses these effects. Inoculation of SK-Hep-1 cancer cells in which HURP has been silenced produces smaller tumors than control in nude mice. Besides, gankyrin, a positive regulator of the E3 ubiquitin ligase MDM2, is upregulated following HURP expression, and silencing of gankyrin reduces HURP-mediated downregulation of p53. In addition, we observed a positive correlation between HURP and gankyrin protein levels in HCC patients (r (2) = 0.778; n = 9). These findings suggest a role for the viral protein HBx and the host protein HURP in preventing p53-mediated apoptosis during cancer progression and establishment of chemoresistance.

Elevated Expression of Hepatoma Up-Regulated Protein Inhibits γ-Irradiation-Induced Apoptosis of Prostate Cancer Cells.

Despite progression in diagnosis and treatment, prostate cancer (PCa) still represents the main cause of cancer-related mortality and morbidity in men. Although radiation therapy offers clinical benefit over other therapeutic modalities, the success of this therapeutic modality is commonly hampered by the resistance of advanced tumors. So far, the mechanisms governing tumor resistance to radiotherapy are not discussed in detail. Here, we demonstrate for the first time that the resistance of PCa to radiation therapy is attributed to elevated expression of Hepatoma Up-Regulated Protein (HURP). In PCa cells, the induction of HURP expression suppresses γ-irradiation-induced apoptosis. γ-irradiation-induced apoptosis of PCa cells is associated with expression of E2F1, p53, p21 proteins together with the phosphorylation of apoptosis signal-regulating kinase1 (ASK1), c-jun-N-terminal kinase (JNK) and Ataxia-telangiectasia mutated (ATM) and histone family member X (H2AX). Whereas, the induction of HURP expression is able to suppress γ-irradiation-induced effects on E2F1, p53, p21, ATM, ASK1, JNK and ATM, and H2AX. Also, inhibition of γ-irradiation-induced- cytochrome c release, cleavage of caspase-9, caspase-3, PARP, and reactive oxygen species (ROS) were noted in PCa cells induced for HURP expression. The observed radio-resistance of PCa is thought to be the consequence of HURP-mediated destabilization of p53 and ATM proteins that are essential for the modulation of γ-irradiation-induced apoptosis. Thus, based on our findings, PCa resistance to radiation therapy results from the deregulation of ASK1/ JNK; ATM/ H2AX; ATM/p53 and checkpoint kinase 2 (Chk2)/ E2F-1 in response to the elevated expression of HURP.