Farnesylated RhoB inhibits radiation-induced mitotic cell death and controls radiation-induced centrosome overduplication

Engineered model of heart tissue repair for exploring fibrotic processes and therapeutic interventions

Advancements in human-engineered heart tissue have enhanced the understanding of cardiac cellular alteration. Nevertheless, a human model simulating pathological remodeling following myocardial infarction for therapeutic development remains essential. Here we develop an engineered model of myocardial repair that replicates the phased remodeling process, including hypoxic stress, fibrosis, and electrophysiological dysfunction. Transcriptomic analysis identifies nine critical signaling pathways related to cellular fate transitions, leading to the evaluation of seventeen modulators for their therapeutic potential in a mini-repair model. A scoring system quantitatively evaluates the restoration of abnormal electrophysiology, demonstrating that the phased combination of TGFβ inhibitor SB431542, Rho kinase inhibitor Y27632, and WNT activator CHIR99021 yields enhanced functional restoration compared to single factor treatments in both engineered and mouse myocardial infarction model. This engineered heart tissue repair model effectively captures the phased remodeling following myocardial infarction, providing a crucial platform for discovering therapeutic targets for ischemic heart disease.

Visualizing the subcellular localization of RHOB-GTP and GTPase-Effector complexes using a split-GFP/nanobody labelling assay

Small GTPases are highly regulated proteins that control essential signaling pathways through the activity of their effector proteins. Among the RHOA subfamily, RHOB regulates peculiar functions that could be associated with the control of the endocytic trafficking of signaling proteins. Here, we used an optimized assay based on tripartite split-GFP complementation to localize GTPase-effector complexes with high-resolution. The detection of RHOB interaction with the Rhotekin Rho binding domain (RBD) that specifically recognizes the active GTP-bound GTPase, is performed in vitro by the concomitant addition of recombinant GFP1-9 and a GFP nanobody. Analysis of RHOB-RBD complexes localization profiles combined with immunostaining and live cell imaging indicated a serum-dependent reorganization of the endosomal and membrane pool of active RHOB. We further applied this technology to the detection of RHO-effector complexes that highlighted their subcellular localization with high resolution among the different cellular compartments.

RhoB as a tumor suppressor: It’s all about localization

The small GTPase RhoB is distinguished from other Rho proteins by its unique subcellular localization in endosomes, multivesicular bodies, and nucleus. Despite high sequence homology with RhoA and RhoC, RhoB is mainly associated with tumor suppressive function, while RhoA and RhoC support oncogenic transformation in most malignancies. RhoB regulates the endocytic trafficking of signaling molecules and cytoskeleton remodeling, thereby controlling growth, apoptosis, stress response, immune function, and cell motility in various contexts. Some of these functions may be ascribed to RhoB's unique subcellular localization to endocytic compartments. Here we describe the pleiotropic roles of RhoB in cancer suppression in the context of its subcellular localization, and we discuss possible therapeutic avenues to pursue and highlight priorities for future research.

High-content tripartite split-GFP cell-based assays to screen for modulators of small GTPase activation

The human Ras superfamily of small GTPases controls essential cellular processes such as gene expression and cell proliferation. As their deregulation is widely associated with human cancer, small GTPases and their regulatory proteins have become increasingly attractive for the development of novel therapeutics. Classical methods to monitor GTPase activation include pulldown assays that limit the analysis of GTP-bound form of proteins from cell lysates. Alternatively, live-cell FRET biosensors may be used to study GTPase activation dynamics in response to stimuli, but these sensors often require further optimization for high-throughput applications. Here, we describe a cell-based approach that is suitable to monitor the modulation of small GTPase activity in a high-content analysis. The assay relies on a genetically encoded tripartite split-GFP (triSFP) system that we integrated in an optimized cellular model to monitor modulation of RhoA and RhoB GTPases. Our results indicate the robust response of the reporter, allowing the interrogation of inhibition and stimulation of Rho activity, and highlight potential applications of this method to discover novel modulators and regulators of small GTPases and related protein-binding domains.

Summary: The development of a fluorescent reporter of GTPase activation based on tripartite split-GFP that enables the evaluation of GEF activity and the effect of modulators of GTPase activation in a high-content analysis.

Inhibition of Farnesyltransferase Potentiates NOTCH-Targeted Therapy against Glioblastoma Stem Cells

Accumulating evidence suggests that cancer cells with stem cell-like phenotypes drive disease progression and therapeutic resistance in glioblastoma (GBM). NOTCH regulates self-renewal and resistance to chemoradiotherapy in GBM stem cells. However, NOTCH-targeted γ-secretase inhibitors (GSIs) exhibited limited efficacy in GBM patients. We found that farnesyltransferase inhibitors (FTIs) significantly improved sensitivity to GSIs. This combination showed significant antineoplastic and radiosensitizing activities in GBM stem cells, whereas non-stem GBM cells were resistant. These combinatorial effects were mediated, at least partially, through inhibition of AKT and cell-cycle progression. Using subcutaneous and orthotopic GBM models, we showed that the combination of FTIs and GSIs, but not either agent alone, significantly reduced tumor growth. With concurrent radiation, this combination induced a durable response in a subset of orthotopic tumors. These findings collectively suggest that the combination of FTIs and GSIs is a promising therapeutic strategy for GBM through selectively targeting the cancer stem cell subpopulation.

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NOTCH signaling is preferentially activated in glioblastoma stem cells

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GSIs have limited activities against glioblastoma stem cells

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FTIs improve response to GSIs in vitro and in vivo

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The combination of FTIs and GSIs makes glioblastoma more sensitive to radiation

FGFR1 Induces Glioblastoma Radioresistance through the PLCγ/Hif1α Pathway

FGF2 signaling in glioblastoma induces resistance to radiotherapy, so targeting FGF2/FGFR pathways might offer a rational strategy for tumor radiosensitization. To investigate this possibility, we evaluated a specific role for FGFR1 in glioblastoma radioresistance as modeled by U87 and LN18 glioblastomas in mouse xenograft models. Silencing FGFR1 decreased radioresistance in a manner associated with radiation-induced centrosome overduplication and mitotic cell death. Inhibiting PLCγ (PLCG1), a downstream effector signaling molecule for FGFR1, was sufficient to produce similar effects, arguing that PLCγ is an essential mediator of FGFR1-induced radioresistance. FGFR1 silencing also reduced expression of HIF1α, which in addition to its roles in hypoxic responses exerts an independent effect on radioresistance. Finally, FGFR1 silencing delayed the growth of irradiated tumor xenografts, in a manner that was associated with reduced HIF1α levels but not blood vessel alterations. Taken together, our results offer a preclinical proof of concept that FGFR1 targeting can degrade radioresistance in glioblastoma, a widespread problem in this tumor, prompting clinical investigations of the use of FGFR1 inhibitors for radiosensitization. Cancer Res; 76(10); 3036-44. ©2016 AACR.

Nanomedicine to overcome radioresistance in glioblastoma stem-like cells and surviving clones

Radiotherapy is one of the standard treatments for glioblastoma, but its effectiveness often encounters the phenomenon of radioresistance. This resistance was recently attributed to distinct cell contingents known as glioblastoma stem-like cells (GSCs) and dominant clones. It is characterized in particular by the activation of signaling pathways and DNA repair mechanisms. Recent advances in the field of nanomedicine offer new possibilities for radiosensitizing these cell populations. Several strategies have been developed in this direction, the first consisting of encapsulating a contrast agent or synthesizing metal-based nanocarriers to concentrate the dose gradient at the level of the target tissue. In the second strategy the physicochemical properties of the vectors are used to encapsulate a wide range of pharmacological agents which act in synergy with the ionizing radiation to destroy the cancerous cells. This review reports on the various molecular anomalies present in GSCs and the predominant role of nanomedicines in the development of radiosensitization strategies.

Critical functions of RhoB in support of glioblastoma tumorigenesis

BACKGROUND

RhoB is a member of the Rho small GTPase family that regulates cytoskeletal dynamics and vesicle trafficking. The RhoB homologs, RhoA and RhoC, have been shown to promote cancer progression and metastasis. In contrast, the functions of RhoB in human cancers are context dependent. Although expression of RhoB inversely correlates with disease progression in several epithelial cancers, recent data suggest that RhoB may support malignant phenotypes in certain cancer types.

METHODS

We assessed RhoB protein levels in glioma surgical specimens and patient-derived xenografts. The roles of RhoB in glioblastoma were determined by loss-of-function and gain-of-function assays in vitro and in vivo. The impact on p53 and STAT3 signaling was investigated.

RESULTS

RhoB expression was similar in tumor specimens compared with normal neural tissues obtained from epilepsy surgery. RhoB was expressed in the vast majority of xenograft tumors and spheroid cultures. Knockdown of RhoB induced cell-cycle arrest and apoptosis and compromised in vivo tumorigenic potential. However, overexpression of wild-type RhoB or a constitutively active mutant (RhoB-V14) did not significantly affect cell growth, which suggests that RhoB is not a rate-limiting oncogenic factor and is consistent with the scarcity of RhoB mutations in human cancer. Knockdown of RhoB reduced basal STAT3 activity and impaired cytokine-induced STAT3 activation. In glioblastoma tumors retaining wild-type p53, depletion of RhoB also activated p53 and induced expression of p21(CIP1) (/WAF1).

CONCLUSIONS

Our data suggest that RhoB belongs to an emerging class of "nononcogene addiction" factors that are essential for maintenance of malignant phenotypes in human cancers.

RhoB promotes cancer initiation by protecting keratinocytes from UVB-induced apoptosis but limits tumor aggressiveness

The role of UVB-induced apoptosis in the formation of squamous cell carcinoma (SCC) is recognized. We previously identified the small RhoB (Ras homolog gene family, member B) GTPase, an early response gene to cellular stress, as a critical protein controlling apoptosis of human keratinocytes after UVB exposure. Here we generated SKH1 (hairless immunocompetent mouse) mice invalidated for RhoB to evaluate its role in UVB-induced skin carcinogenesis in vivo. We show that rhob-/- mice have a lower risk of developing UVB-induced keratotic tumors and actinic keratosis that is associated with a higher sensitivity of UVB-exposed keratinocytes to apoptosis. We extend this observation to primary cultures of normal human keratinocytes in which RhoB was downregulated with small interfering RNA (siRNA) and further show that the hypersensitivity to apoptosis depends on B-cell lymphoma 2 (Bcl-2) downregulation. In rhob-/- mice, the UVB-induced tumors were preferentially undifferentiated and highly proliferative. Finally, we show in humans an almost constant loss of RhoB expression in undifferentiated SCCs. These undifferentiated and RhoB-deficient tumors have elevated phosphorylated histone H2AX (γH2AX) and 53BP1, two markers of DNA double-strand breaks. Together, our results indicate that UVB-induced RhoB expression participates in in vivo SCC initiation by increasing keratinocyte survival. Conversely, RhoB may limit tumor aggressiveness as loss of RhoB expression in tumor cells is associated with tumor progression.

Radiation-induced mitotic cell death and glioblastoma radioresistance: a new regulating pathway controlled by integrin-linked kinase, hypoxia-inducible factor 1 alpha and survivin in U87 cells

We have previously shown that integrin-linked kinase (ILK) regulates U87 glioblastoma cell radioresistance by modulating the main radiation-induced cell death mechanism in solid tumours, the mitotic cell death. To decipher the biological pathways involved in these mechanisms, we constructed a U87 glioblastoma cell model expressing an inducible shRNA directed against ILK (U87shILK). We then demonstrated that silencing ILK enhanced radiation-induced centrosome overduplication, leading to radiation-induced mitotic cell death. In this model, ionising radiations induce hypoxia-inducible factor 1 alpha (HIF-1α) stabilisation which is inhibited by silencing ILK. Moreover, silencing HIF-1α in U87 cells reduced the surviving fraction after 2 Gy irradiation by increasing cell sensitivity to radiation-induced mitotic cell death and centrosome amplification. Because it is known that HIF-1α controls survivin expression, we then looked at the ILK silencing effect on survivin expression. We show that survivin expression is decreased in U87shILK cells. Furthermore, treating U87 cells with the specific survivin suppressor YM155 significantly increased the percentage of giant multinucleated cells, centrosomal overduplication and thus U87 cell radiosensitivity. In consequence, we decipher here a new pathway of glioma radioresistance via the regulation of radiation-induced centrosome duplication and therefore mitotic cell death by ILK, HIF-1α and survivin. This work identifies new targets in glioblastoma with the intention of radiosensitising these highly radioresistant tumours.

αvβ3 Integrin and Fibroblast growth factor receptor 1 (FGFR1): Prognostic factors in a phase I-II clinical trial associating continuous administration of Tipifarnib with radiotherapy for patients with newly diagnosed glioblastoma

BACKGROUND

Based on our previous results showing the involvement of the farnesylated form of RhoB in glioblastoma radioresistance, we designed a phase II trial associating the farnesyltransferase inhibitor Tipifarnib with radiotherapy in patients with glioblastoma and studied the prognostic values of the proteins which we have previously shown control this pathway.

PATIENTS AND METHODS

Patients were treated with 200mg Tipifarnib (recommended dose (RD)) given continuously during radiotherapy. Twenty-seven patients were included in the phase II whose primary end-point was time to progression (TTP). Overall survival (OS) and biomarker analysis were secondary end-points. Expressions of αvβ3, αvβ5 integrins, FAK, ILK, fibroblast growth factor 2 (FGF2) and fibroblast growth factor receptor 1 (FGFR1) were studied by immuno-histochemistry in the tumour of the nine patients treated at the RD during the previously performed phase I and on those of the phase II patients. We evaluated the correlation of the expressions of these proteins with the clinical outcome.

RESULTS

For the phase II patients median TTP was 23.1 weeks (95%CI = [15.4; 28.2]) while the median OS was 80.3 weeks (95%CI = [57.8; 102.7]). In the pooled phase I and II population, median OS was 60.4 w (95%CI = [47.3; 97.6]) while median TTP was 18.1 w (95%CI = [16.9; 25.6]). FGFR1 over-expression (HR = 4.65; 95%CI = [1.02; 21.21], p = 0.047) was correlated with shorter TTP while FGFR1 (HR = 4.1 (95% CI = [1.09-15.4]; p = 0.036)) and αvβ3 (HR = 10.38 (95%CI = [2.70; 39.87], p = 0.001)) over-expressions were associated with reduced OS.

CONCLUSION

Association of 200mg Tipifarnib with radiotherapy shows promising OS but no increase in TTP compared to historical data. FGFR1 and αvβ3 integrin are independent bad prognostic factors of OS and TTP.

Cytoprotective effect of the small GTPase RhoB expressed upon treatment of fibroblasts with the Ras-glucosylating Clostridium sordellii lethal toxin

Mono-glucosylation of (H/K/N)Ras by Clostridium sordellii lethal toxin (TcsL) blocks critical survival signaling pathways, resulting in apoptosis. In this study, TcsL and K-Ras knock-down by siRNA are presented to result in expression of the cell death-regulating small GTPase RhoB. TcsL-induced RhoB expression is based on transcriptional activation involving p38(alpha) MAP kinase. Newly synthesized RhoB protein is rapidly degraded in a proteasome- and a caspase-dependent manner, providing first evidence for caspase-dependent degradation of a Rho family protein. Although often characterised as a pro-apoptotic protein, RhoB suppresses caspase-3 activation in TcsL-treated fibroblasts. The finding on the cytoprotective activity of RhoB in TcsL-treated cells re-enforces the concept that RhoB exhibits cytoprotective rather than pro-apoptotic activity in a cellular background of inactive Ras.

[Optimization of the radiotherapy for the gliomas: hopes and research axis for the next future]

Glioma and particularly glioblastoma are tumours of very bad prognosis despite association of surgery and radiochemotherapy. This bad prognosis is mainly due to the local relapse after radiochemotherapy which occurs invariably despite constant technical progress in radiotherapy. This local recurrence is mainly due to the biologic intracellular and micro-environmental radioresistance of these tumours but also to a probable bad definition of the irradiated target. The two main axis of research aiming at optimizing the radiotherapy of these patients will be discussed: on one hand, the study of the biological pathways involved in the tumor radioresistance in order to highlight new targets of interest and to inhibit them by targeted drugs in combination with radiotherapy, and on the other hand, research in metabolic and functional imaging with the aim to define areas of most aggressive disease and even predictive zones of the site of relapse and thus of radioresistance, in order to integrate them in the radiotherapy treatment planning in prospective trials.

RhoB deficiency in thymic medullary epithelium leads to early thymic atrophy

RhoB, a member of the Rho subfamily of small GTPases, mediates diverse cellular functions, including cytoskeletal organization, cell transformation and vesicle trafficking. The thymus undergoes progressive decline in its structure and function after puberty. We found that RhoB was expressed in thymic medullary epithelium. To investigate a role of RhoB in the regulation of thymic epithelial organization or thymocyte development, we analyzed the thymi of RhoB-deficient mice. RhoB-deficient mice were found to display earlier thymic atrophy. RhoB deficiency showed significant reductions in thymus weight and cellularity, beginning as early as 5 weeks of age. The enhanced expression of TGF-β receptor type II (TGFβRII) in thymic medullary epithelium was observed in RhoB-null mice. In addition, the expression of fibronectin, which is shown to be regulated by TGF-β signaling, was accordingly increased in the mutant thymic medulla. Since there is no age-related change of RhoB expression in the thymus, it is unlikely that RhoB in thymic epithelium directly contributes to age-related thymic involution. Nevertheless, our findings strongly support a physiological role of RhoB in regulation of thymus development and maintenance through the inhibition of TGF-β signaling in thymic medullary epithelium.

Induction of small G protein RhoB by non-genotoxic stress inhibits apoptosis and activates NF-κB

It has been reported by us and other groups that the expression of small GTP binding protein RhoB can be induced by genotoxic stressors and glucocorticoid (GC), a stress hormone that plays a key role in stress response. Until now stress-induced genes that confer cytoprotection under stressed conditions are largely unknown. In this study, we investigated the effects and mechanism of non-genotoxic stressors, including scalding in vivo and heat stress in vitro on the expression of RhoB. We found for the first time that both scalding, which could induce typical neuroendocrine responses of acute stress and cellular heat stress significantly increased the expression of RhoB at mRNA and protein levels. Moreover, in vitro experiments in human lung epithelial cells (A549) showed that induction of RhoB by heat stress was in a glucocorticoid receptor (GR)-independent manner and through multiple pathways including stabilization of RhoB mRNA and activation of p38 MAPK. Further experiments demonstrated that up-regulation of RhoB significantly inhibited heat stress-induced apoptosis and elevated transcriptional activity of NF-κB, but did not affect the expression of Hsp70 in A549 cells. In conclusion, we showed for the first time that RhoB was up-regulated by scalding in vivo and heat stress in vitro and played an important cytoprotective role during heat stress-induced apoptotic cell death.

Systematic analyses of genes associated with radiosensitizing effect by celecoxib, a specific cyclooxygenase-2 inhibitor

To investigate genes regulated by COX-2 or a COX-2 specific inhibitor, celecoxib, in irradiated cancer cells, we analyzed changes in gene expression using complementary DNA microarray following celecoxib or combined celecoxib and ionizing radiation (IR) treatment in a stable COX-2 knockdown A549 (AS) and a mock cell line (AN). Thirty-six genes were differentially expressed by COX-2 knockdown. Celecoxib changed the expressions of 40 and 69 genes in AN and AS cells, respectively. Twenty-seven genes were synchronously regulated by COX-2 and celecoxib. Among these, celecoxib regulated ras homolog gene family B and mitosin protein expression in a COX-2 dependent manner, especially in irradiated cells. In addition, we identified 11 genes that changed by more than 1.5 times the expected additive values after celecoxib and IR treatment. The current study may provide evidence that COX-2 or celecoxib regulates various intracellular functions in addition to their enzymatic activity regulation. We also identified candidate molecules that may be responsible for COX-2-dependent radiosensitization by celecoxib.

RhoA and RhoC are both required for the ROCK II-dependent promotion of centrosome duplication

CDK2-cyclin E triggers centrosome duplication, and nucleophosmin (NPM/B23) is found to be one of its targets. NPM/B23 phosphorylated by CDK2-cyclin E acquires a high binding affinity to Rho-associated kinase (ROCK II), and physically associates with ROCK II. The NPM/B23-binding results in superactivation of ROCK II, which is a critical event for initiation of centrosome duplication. The activation of ROCK II also requires the binding of Rho small GTPase to the auto-inhibitory region; hence the availability of the active Rho protein is an important aspect of the centrosomally localized ROCK II to properly initiate centrosome duplication. There are three isoforms of Rho (RhoA, B and C), all of which are capable of binding to and priming the activation of ROCK II. Here, we investigated which Rho isoform(s) are involved in the activation of ROCK II in respect to the initiation of centrosome duplication. We found that both RhoA and RhoC, but not RhoB, were required for initiation of centrosome duplication, and overactivation of RhoA, as well as RhoC, but not RhoB, promoted centrosome duplication and centrosome amplification.

Phosphorylation of RhoB by CK1 impedes actin stress fiber organization and epidermal growth factor receptor stabilization

RhoB is a small GTPase implicated in cytoskeletal organization, EGF receptor trafficking and cell transformation. It is an immediate-early gene, regulated at many levels of its biosynthetic pathway. Herein we show that the serine/threonine protein kinase CK1 phosphorylates RhoB in vitro but not RhoA or RhoC. With the use of specific CK1 inhibitors, IC261 and D4476, we show that the kinase phosphorylates also RhoB in HeLa cells. Mass spectrometry analysis demonstrates that RhoB is monophosphorylated by CK1, in its C-terminal end, on serine 185. The substitution of Ser185 by Ala dramatically inhibited the phosphorylation of RhoB in cultured cells. Lastly we show that the inhibition of CK1 activates RhoB and promotes RhoB dependent actin fiber formation and EGF-R level. Our data provide the first demonstration of RhoB phosphorylation and indicate that this post-translational maturation would be a novel critical mechanism to control the RhoB functions.

Alphavbeta3 and alphavbeta5 integrins control glioma cell response to ionising radiation through ILK and RhoB

Integrins are extracellular matrix receptors involved in tumour invasion and angiogenesis. Although there is evidence that inhibiting integrins might enhance the efficiency of radiotherapy, little is known about the exact mechanisms involved in the integrin-dependent modulation of tumor radiosensitivity. The purpose of this study was to investigate the role of alphavbeta3 and alphavbeta5 integrins in glioblastoma cell radioresistance and overall to decipher the downstream biological pathways. We first demonstrated that silencing alphavbeta3 and alphavbeta5 integrins with specific siRNAs significantly reduced the survival after irradiation of 2 glioblastoma cell lines: U87 and SF763. We then showed that integrin activity and integrin signalling pathways controlled the glioma cell radiosensitivity. This regulation of glioma cell response to ionising radiation was mediated through the integrin-linked kinase, ILK, and the small GTPase, RhoB, by two mechanisms. The first one, independent of ILK, consists in the regulation of the intracellular level of RhoB by alphavbeta3 or alphavbeta5 integrin. The second pathway involved in cell radiosensitivity consists in RhoB activation by ionising radiation through ILK. Furthermore, we demonstrated that the alphavbeta3/alphavbeta5 integrins/ILK/RhoB pathway controlled the glioma cells radiosensitivity by regulating radiation-induced mitotic cell death. This work identifies a new biological pathway controlling glioblastoma cells radioresistance, activated from the membrane through alphavbeta3 and/or alphavbeta5 integrins via ILK and RhoB. Our results are clues that downstream effectors of alphavbeta3 and alphavbeta5 integrins as ILK and RhoB might also be promising candidate targets for improving the efficiency of radiotherapy and thus the clinical outcome of patients with glioblastoma.

Proton magnetic resonance spectroscopic imaging in newly diagnosed glioblastoma: predictive value for the site of postradiotherapy relapse in a prospective longitudinal study

PURPOSE

To investigate the association between magnetic resonance spectroscopic imaging (MRSI)-defined, metabolically abnormal tumor regions and subsequent sites of relapse in data from patients treated with radiotherapy (RT) in a prospective clinical trial.

METHODS AND MATERIALS

Twenty-three examinations were performed prospectively for 9 patients with newly diagnosed glioblastoma multiforme studied in a Phase I trial combining Tipifarnib and RT. The patients underwent magnetic resonance imaging (MRI) and MRSI before treatment and every 2 months until relapse. The MRSI data were categorized by the choline (Cho)/N-acetyl-aspartate (NAA) ratio (CNR) as a measure of spectroscopic abnormality. CNRs corresponding to T1 and T2 MRI for 1,207 voxels were evaluated before RT and at recurrence.

RESULTS

Before treatment, areas of CNR2 (CNR > or =2) represented 25% of the contrast-enhancing (T1CE) regions and 10% of abnormal T2 regions outside T1CE (HyperT2). The presence of CNR2 was often an early indicator of the site of relapse after therapy. In fact, 75% of the voxels within the T1CE+CNR2 before therapy continued to exhibit CNR2 at relapse, compared with 22% of the voxels within the T1CE with normal CNR (p < 0.05). The location of new contrast enhancement with CNR2 corresponded in 80% of the initial HyperT2+CNR2 vs. 20.7% of the HyperT2 voxels with normal CNR (p < 0.05).

CONCLUSION

Metabolically active regions represented a small percentage of pretreatment MRI abnormalities and were predictive for the site of post-RT relapse. The incorporation of MRSI data in the definition of RT target volumes for selective boosting may be a promising avenue leading to increased local control of glioblastomas.

MAP1A light chain-2 interacts with GTP-RhoB to control epidermal growth factor (EGF)-dependent EGF receptor signaling

Rho GTPases have been implicated in the control of several cellular functions, including regulation of the actin cytoskeleton, cell proliferation, and oncogenesis. Unlike RhoA and RhoC, RhoB localizes in part to endosomes and controls endocytic trafficking. Using a yeast two-hybrid screen and a glutathione S-transferase pulldown assay, we identified LC2, the light chain of the microtubule-associated protein MAP1A, as a novel binding partner for RhoB. GTP binding and the 18-amino acid C-terminal hypervariable domain of RhoB are critical for its binding to MAP1A/LC2. Coimmunoprecipitation and immunofluorescence experiments showed that this interaction occurs in U87 cells. Down-regulation of MAP1A/LC2 expression decreased epidermal growth factor (EGF) receptor expression and modified the signaling response to EGF treatment. We concluded that MAP1A/LC2 is critical for RhoB function in EGF-induced EGF receptor regulation. Because MAP1A/LC2 is thought to function as an adaptor between microtubules and other molecules, we postulate that the RhoB and MAP1A/LC2 interactions facilitate endocytic vesicle trafficking and regulate the trafficking of signaling molecules.

ROCK I-mediated activation of NF-kappaB by RhoB

RhoB is a short-lived protein whose expression is increased by a variety of extra-cellular stimuli including UV irradiation, epidermal growth factor (EGF) and transforming growth factor beta (TGF-beta). Whereas most Rho proteins are modified by the covalent attachment of a geranylgeranyl group, RhoB is unique in that it can exist in either a geranylgeranylated (RhoB-GG) or a farnesylated (RhoB-F) form. Although each form is proposed to have different cellular functions, the signaling events that underlie these differences are poorly understood. Here we show that RhoB can activate NF-kappaB signaling in multiple cell types. Whereas RhoB-F is a potent activator of NF-kappaB, much weaker activation is observed for RhoB-GG, RhoA, and RhoC. NF-kappaB activation by RhoB is not associated with increased nuclear translocation of RelA/p65, but rather, by modification of the RelA/p65 transactivation domain. Activation of NF-kappaB by RhoB is dependent upon ROCK I but not PRK I. Thus, ROCK I cooperates with RhoB to activate NF-kappaB, and suppression of ROCK I activity by genetic or pharmacological inhibitors blocks NF-kappaB activation. Suppression of RhoB activity by dominant-inhibitory mutants, or siRNA, blocks NF-kappaB activation by Bcr, and TSG101, but not by TNFalpha or oncogenic Ras. Collectively, these observations suggest the existence of an endosome-associated pathway for NF-kappaB activation that is preferentially regulated by the farnesylated form of RhoB.

Phase I Trial of Tipifarnib (R115777) Concurrent With Radiotherapy in Patients with Glioblastoma Multiforme

PURPOSE

To conduct a Phase I trial to determine the maximally tolerated dose (MTD) of tipifarnib in combination with conventional three-dimensional conformal radiotherapy (RT) for patients with glioblastoma multiforme.

METHODS AND MATERIALS

After resection or biopsy, tipifarnib was given 1 week before and then continuously during RT (60 Gy), followed by adjuvant administration until progression. The tipifarnib dose during RT was escalated in cohorts of 3 starting at 200 mg/day.

RESULTS

Thirteen patients were enrolled, and 12 were evaluable for MTD. Of these patients, 7 had undergone biopsy, 4 had partial resection, and 1 had gross total resection. No dose-limiting toxicity (DLT) was observed during the concomitant treatment at 200 mg. All 3 patients at 300 mg experienced DLT during the concomitant treatment: 1 with sudden death and 2 with acute pneumonitis. The MTD was reached at 300 mg. The adjuvant treatment was suppressed from the protocol after a case of pneumonitis during this treatment. Six additional patients were included at 200 mg/day of the new protocol, confirming the safety of this treatment. Of the 9 evaluable patients, 1 had partial response, 4 had stable disease, and 3 had rapid progression; the patient with gross total resection was relapse-free after 21 months. Median survival of the evaluable patients was 12 months (range, 5.2-21 months).

CONCLUSION

Tipifarnib (200 mg/day) concurrent with standard radiotherapy is well tolerated in patients with glioblastoma. Preliminary efficacy results are encouraging.

Induction of Centrosome Amplification during Arsenite-Induced Mitotic Arrest in CGL-2 Cells

Arsenite-induced mitotic abnormalities result in mitotic death in several cancer cell lines. However, how arsenite induces these effects is not known. We have previously shown that arsenite induces mitotic arrest, mitotic abnormalities, and mitotic death in CGL-2 cells. To further delineate the mechanism of action of arsenite, we examined its effect on centrosome duplication and the possible link between centrosome dysregulation and arsenite-induced mitotic death. Immunofluorescence staining of gamma-tubulin revealed that centrosome amplification was induced in arsenite-arrested mitotic cells but not in nocodazole-arrested cells. When S phase-enriched cells were treated with arsenite, they progressed into and arrested at mitosis and then formed supernumerary centrosomes. A further increase in arsenite-induced centrosome amplification was seen during the prolonged mitotic arrest. The arsenite-induced supernumerary centrosomes might result from uneven fragmentation of centrosome, overexpression of pericentriolar materials, and inhibition of centrosomal coalescence during mitosis. Furthermore, termination of mitotic arrest by treatment of arsenite-arrested mitotic cells with cyclin-dependent kinase 1 inhibitors or by suppression of spindle checkpoint function by small interfering RNA-mediated silencing of BubR1 or Mad2 markedly reduced the induction of centrosome amplification and mitotic death in arsenite-treated cells. These results indicate that centrosome amplification is induced in arsenite-arrested mitotic CGL-2 cells in a spindle checkpoint-dependent manner and is involved in the induction of arsenite-induced mitotic death.

Modulation of cell cycle and gene expression in pancreatic tumor cell lines by methionine deprivation (methionine stress): implications to the therapy of pancreatic adenocarcinoma

The effect of methionine deprivation (methionine stress) on the proliferation, survival, resistance to chemotherapy, and regulation of gene and protein expression in pancreatic tumor lines is examined. Methionine stress prevents successful mitosis and promotes cell cycle arrest and accumulation of cells with multiple micronuclei with decondensed chromatin. Inhibition of mitosis correlates with CDK1 down-regulation and/or inhibition of its function by Tyr(15) phosphorylation or Thr(161) dephosphorylation. Inhibition of cell cycle progression correlates with loss of hyperphosphorylated Rb and up-regulation of p21 via p53 and/or transforming growth factor-beta (TGF-beta) activation depending on p53 status. Although methionine stress-induced toxicity is not solely dependent on p53, the gain in p21 and loss in CDK1 transcription are more enhanced in wild-type p53 tumors. Up-regulation of SMAD7, a TGF-beta signaling inhibitor, suggests that SMAD7 does not restrict the TGF-beta-mediated induction of p21, although it may prevent up-regulation of p27. cDNA oligoarray analysis indicated a pleiotropic response to methionine stress. Cell cycle and mitotic arrest is in agreement with up-regulation of NF2, ETS2, CLU, GADD45alpha, GADD45beta, and GADD45gamma and down-regulation of AURKB, TOP2A, CCNA, CCNB, PRC1, BUB1, NuSAP, IFI16, and BRCA1. Down-regulation of AREG, AGTR1, M-CSF, and EGF, IGF, and VEGF receptors and up-regulation of GNA11 and IGFBP4 signify loss of growth factor support. PIN1, FEN1, and cABL up-regulation and LMNB1, AREG, RhoB, CCNG, TYMS, F3, and MGMT down-regulation suggest that methionine stress sensitizes the tumor cells to DNA-alkylating drugs, 5-fluorouracil, and radiation. Increased sensitivity of pancreatic tumor cell lines to temozolomide is shown under methionine stress conditions and is attributed in part to diminished O(6)-methylguanine-DNA methyltransferase and possibly to inhibition of the cell cycle progression.

RhoB protects human keratinocytes from UVB-induced apoptosis through epidermal growth factor receptor signaling

Exposure of the skin to UVB light results in the formation of DNA photolesions that can give rise to cell death, mutations, and the onset of carcinogenic events. Specific proteins are activated by UVB and then trigger signal transduction pathways that lead to cellular responses. An alteration of these signaling molecules is thought to be a fundamental event in tumor promotion by UVB irradiation. RhoB, encoding a small GTPase has been identified as a DNA damage-inducible gene. RhoB is involved in epidermal growth factor (EGF) receptor trafficking, cytoskeletal organization, cell transformation, and survival. We have analyzed the regulation of RhoB and elucidated its role in the cellular response of HaCaT keratinocytes to relevant environmental UVB irradiation. We report here that the activated GTP-bound form of RhoB is increased rapidly within 5 min of exposure to UVB, and then RhoB protein levels increased concomitantly with EGF receptor (EGFR) activation. Inhibition of UVB-induced EGFR activation prevents RhoB protein expression and AKT phosphorylation but not the early activation of RhoB. Blocking UVB-induced RhoB expression with specific small interfering RNAs inhibits AKT and glycogen synthase kinase-3beta phosphorylation through inhibition of EGFR expression. Moreover, down-regulation of RhoB potentiates UVB-induced cell apoptosis. In contrast, RhoB overexpression protects keratinocytes against UVB-induced apoptosis. These results indicated that RhoB is regulated upon UVB exposure by a two-step process consisting of an early EGFR-independent RhoB activation followed by an EGFR-dependent induction of RhoB expression. Moreover, we have demonstrated that RhoB is essential in regulating keratinocyte cell survival after UVB exposure, suggesting its potential role in photocarcinogenesis.