Generation of PT101, a highly selective IL-2 mutein for treatment of autoimmune diseases

Regulatory T cells (Treg) are vital for immune homeostasis and are dysfunctional in autoimmunity. Interleukin 2 (IL-2) drives the proliferation and function of Tregs via its heterotrimeric receptor (CD25/CD122/CD132). Low dose IL-2 is being evaluated for treatment of autoimmune diseases and has been shown to expand Tregs, yet it has a small selectivity window over conventional T cells (Tconv) and natural killer (NK) cells. To enhance IL-2 selectivity, mutations can be introduced to reduce its CD122/CD132 affinity thus creating a CD25 dependency for signaling through CD122/CD132 upon IL-2 facilitated CD25/CD122/CD132 trimer formation. Using structure guided approach, we introduced mutations in IL-2 that significantly decreased CD122 affinity in addition to mutations that increased CD25 affinity. Finally, we explored other mutations, orientation, and linkers to generate a potent, selective molecule with drug-like manufacturability. These structure activity relationship efforts culminated in the generation of PT101, a mutant IL-2 Fc fusion that was selective in activating and expanding Tregs. PT101 selectively induced STAT5 phosphorylation in human and non-human primate (NHP) Tregs in vitro. In humanized mice and NHPs, administration of PT101 dose-dependently and selectively expanded Treg without significant effects on other immune cell types, nor eliciting proinflammatory cytokine production. In a Phase 1a clinical trial, PT101 was well-tolerated and selectively expanded total Tregs by up to a mean maximum of 3.6-fold. There was no evidence of expansion of NK cells nor pro-inflammatory Tconv at any dose studied. Clinical trials in patients with ulcerative colitis and systemic lupus erythematosus are planned with PT101.

HLA-Restriction of Human Treg Cells Is Not Required for Therapeutic Efficacy of Low-Dose IL-2 in Humanized Mice

Regulatory T (T_reg) cells are essential to maintain immune homeostasis in the intestine and T_reg cell dysfunction is associated with several inflammatory and autoimmune disorders including inflammatory bowel disease (IBD). Efforts using low-dose (LD) interleukin-2 (IL-2) to expand autologous T_reg cells show therapeutic efficacy for several inflammatory conditions. Whether LD IL-2 is an effective strategy for treating patients with IBD is unknown. Recently, we demonstrated that LD IL-2 was protective against experimental colitis in immune humanized mice in which human CD4⁺ T cells were restricted to human leukocyte antigen (HLA). Whether HLA restriction is required for human T_reg cells to ameliorate colitis following LD IL-2 therapy has not been demonstrated. Here, we show that treatment with LD IL-2 reduced 2,4,6-trinitrobenzensulfonic acid (TNBS) colitis severity in NOD.Prkdc^scidIl2rg^-/- (NSG) mice reconstituted with human CD34⁺ hematopoietic stem cells. These data demonstrate the utility of standard immune humanized NSG mice as a pre-clinical model system to evaluate therapeutics targeting human T_reg cells to treat IBD.

Surgical induction of posttraumatic osteoarthritis in the mouse

Given the prevalence and the scope of the personal and societal burden of OA, investigators have become increasingly interested in understanding the pathogenic basis of disease and developing novel disease-modifying OA therapies. Because of the well-documented central role that joint trauma plays in the initiation of knee OA, large animal and rodent models of knee injury that accurately recapitulate the OA disease process have become increasingly widespread over the past decade. To enable study in the context of defined genetic backgrounds, investigative teams have informally developed standardized protocols for injuring the mouse knee that aim to induce a reproducible degenerative process both in terms of severity and temporal pacing of disease progression. One such procedure, the meniscal/ligamentous injury (MLI) model of posttraumatic OA, is described in detail in this chapter. The description provided here sets the stage for both inexperienced and established investigators to employ the MLI procedure, or other similar surgical destabilization methods, to initiate the development of posttraumatic OA in the mouse. Successful application of this method provides a preclinical platform to study the mechanisms driving the pathogenesis of OA and to develop chondroprotective/regenerative strategies to treat it.

MMP13 is a critical target gene during the progression of osteoarthritis

INTRODUCTION

Osteoarthritis (OA) is a degenerative joint disease affecting a large population of people. The mechanism of this highly prevalent disease is not fully understood. Currently there is no effective disease-modifying treatment for OA. The purpose of this study was two-fold: 1) to investigate the role of MMP13 in the development of OA; and 2) to evaluate the efficacy of the MMP13 inhibitor CL82198 as a pharmacologic treatment for preventing OA progression.

METHODS

To investigate the role of the endogenous Mmp13 gene in OA development, tamoxifen was administered to two-week-old Col2CreER;Mmp13fx/fx (Mmp13Col2ER) and Cre-negative control mice for five days. OA was induced by meniscal-ligamentous injury (MLI) when the mice were 10 weeks old and MLI or sham-operated joints were harvested 4, 8, 12, or 16 weeks after surgery. To evaluate the efficacy of CL82198, MLI surgery was performed on 10-week-old wild type mice. CL82198 or saline was administered to the mice daily beginning immediately after the surgery for up to 16 weeks. The joint tissues collected from both experiments were evaluated by cartilage grading, histology/histomorphometry, immunohistochemistry (IHC), and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining. The ability of CL82198 to inhibit MMP13 activity in vitro was confirmed by ELISA.

RESULTS

The OA progression was decelerated in Mmp13Col2ER mice 8, 12, and 16 weeks post-surgery. Cartilage grading by blinded observers confirmed decreased articular cartilage degeneration in Mmp13Col2ER mice at 8, 12 and 16 weeks compared to Cre-negative mice. Histomorphometric analysis demonstrated that Mmp13Col2ER mice had a higher articular cartilage area and thickness at 12 and 16 weeks post-surgery compared to the control mice. Results of IHC revealed greater type II collagen and proteoglycan expression in Mmp13Col2ER mice. Chondrocyte apoptosis, as determined by TUNEL staining, was higher in control mice compared to Mmp13Col2ER mice. CL82198 inhibited MMP13 activity in conditioned media from vehicle (>85%) or bone morphogenetic protein 2 (BMP2)-treated (>90%) primary murine sternal chondrocytes. Intraperitoneal injection of CL82198 decelerated MLI-induced OA progression, increased type II collagen and proteoglycan levels, and inhibited chondrocyte apoptosis compared to saline treatment as determined by OA grading, histology, histomorphometry, IHC, and TUNEL staining, respectively.

CONCLUSIONS

Mmp13 is critical for OA progression and pharmacologic inhibition of MMP13 is an effective strategy to decelerate articular cartilage loss in a murine model of injury-induced knee OA.

Conditional activation of β-catenin signaling in mice leads to severe defects in intervertebral disc tissue

OBJECTIVE

The incidence of low back pain is extremely high and is often linked to intervertebral disc (IVD) degeneration. The mechanism of this disease is currently unknown. This study was undertaken to investigate the role of β-catenin signaling in IVD tissue function.

METHODS

β-catenin protein levels were measured by immunohistochemical analysis of disc samples obtained from patients with disc degeneration and from normal subjects. To generate β-catenin conditional activation (cAct) mice, Col2a1-CreER(T2) -transgenic mice were bred with β-catenin(fx(Ex3)/fx(Ex3)) mice. Changes in disc tissue morphology and function were examined by micro-computed tomography, histologic analysis, and real-time polymerase chain reaction assays.

RESULTS

β-catenin protein was up-regulated in disc tissue samples from patients with disc degeneration. To assess the effects of increased β-catenin levels on disc tissue, we generated β-catenin cAct mice. Overexpression of β-catenin in disc cells led to extensive osteophyte formation in 3- and 6-month-old β-catenin cAct mice, which were associated with significant changes in the cells and extracellular matrix of disc tissue and growth plate. Gene expression analysis demonstrated that activation of β-catenin enhanced runt-related transcription factor 2-dependent Mmp13 and Adamts5 expression. Moreover, genetic ablation of Mmp13 or Adamts5 on the β-catenin cAct background, or treatment of β-catenin cAct mice with a specific matrix metalloproteinase 13 inhibitor, ameliorated the mutant phenotype.

CONCLUSION

Our findings indicate that the β-catenin signaling pathway plays a critical role in disc tissue function.

Lead induces an osteoarthritis-like phenotype in articular chondrocytes through disruption of TGF-β signaling

Lead remains a significant environmental toxin, and we believe we may have identified a novel target of lead toxicity in articular chondrocytes. These cells are responsible for the maintenance of joint matrix, and do so under the regulation of TGF-β signaling. As lead is concentrated in articular cartilage, we hypothesize that it can disrupt normal chondrocyte phenotype through suppression of TGF-β signaling. These experiments examine the effects of lead exposure in vivo and in vitro at biologically relevant levels, from 1 nM to 10 µM on viability, collagen levels, matrix degrading enzyme activity, TGF-β signaling, and articular surface morphology. Our results indicate that viability was unchanged at levels ≤100 µM Pb, but low and high level lead in vivo exposure resulted in fibrillation and degeneration of the articular surface. Lead treatment also decreased levels of type II collagen and increased type X collagen, in vivo and in vitro. Additionally, MMP13 activity increased in a dose-dependent manner. Active caspase 3 and 8 were dose-dependently elevated, and treatment with 10 µM Pb resulted in increases of 30% and 500%, respectively. Increasing lead treatment resulted in a corresponding reduction in TGF-β reporter activity, with a 95% reduction at 10µM. Levels of phosphoSmad2 and 3 were suppressed in vitro and in vivo and lead dose-dependently increased Smurf2. These changes closely parallel those seen in osteoarthritis. Over time this phenotypic shift could compromise maintenance of the joint matrix.

Ski inhibits TGF-β/phospho-Smad3 signaling and accelerates hypertrophic differentiation in chondrocytes

Since transforming growing factor-β (TGF-β)/Smad signaling inhibits chondrocyte maturation, endogenous negative regulators of TGF-β signaling are likely also important regulators of the chondrocyte differentiation process. One such negative regulator, Ski, is an oncoprotein that is known to inhibit TGF-β/Smad3 signaling via its interaction with phospho-Smad3 and recruitment of histone deacetylases (HDACs) to the DNA binding complex. Based on this, we hypothesized that Ski inhibits TGF-β signaling and accelerates maturation in chondrocytes via recruitment of HDACs to transcriptional complexes containing Smads. We tested this hypothesis in chick upper sternal chondrocytes (USCs), where gain and loss of Ski expression experiments were performed. Over-expression of Ski not only reversed the inhibitory effect of TGF-β on the expression of hypertrophic marker genes such as type X collagen (colX) and osteocalcin, it induced these genes basally as well. Conversely, knockdown of Ski by RNA interference led to a reduction of colX and osteocalcin expression under basal conditions. Furthermore, Ski blocked TGF-β induction of cyclinD1 and caused a basal up-regulation of Runx2, consistent with the observed acceleration of hypertrophy. Regarding mechanism, not only does Ski associate with phospho-Smad2 and 3, but its association with phospho-Smad3 is required for recruitment of HDAC4 and 5. Implicating this recruitment of HDACs in the phenotypic effects of Ski in chondrocytes, the HDAC inhibitor SAHA reversed the up-regulation of colX and osteocalcin in Ski over-expressing cells. These results suggest that inhibition of TGF-β signaling by Ski, which involves its association with phospho-Smad3 and recruitment of HDAC4 and 5, leads to accelerated chondrocyte differentiation.

Gene signature critical to cancer phenotype as a paradigm for anticancer drug discovery

Malignant cell transformation commonly results in the deregulation of thousands of cellular genes, an observation that suggests a complex biological process and an inherently challenging scenario for the development of effective cancer interventions. To better define the genes/pathways essential to regulating the malignant phenotype, we recently described a novel strategy based on the cooperative nature of carcinogenesis that focuses on genes synergistically deregulated in response to cooperating oncogenic mutations. These so-called 'cooperation response genes' (CRGs) are highly enriched for genes critical for the cancer phenotype, thereby suggesting their causal role in the malignant state. Here, we show that CRGs have an essential role in drug-mediated anticancer activity and that anticancer agents can be identified through their ability to antagonize the CRG expression profile. These findings provide proof-of-concept for the use of the CRG signature as a novel means of drug discovery with relevance to underlying anticancer drug mechanisms.

Teriparatide as a chondroregenerative therapy for injury-induced osteoarthritis

There is no disease-modifying therapy for osteoarthritis, a degenerative joint disease that is projected to afflict more than 67 million individuals in the United States alone by 2030. Because disease pathogenesis is associated with inappropriate articular chondrocyte maturation resembling that seen during normal endochondral ossification, pathways that govern the maturation of articular chondrocytes are candidate therapeutic targets. It is well established that parathyroid hormone (PTH) acting via the type 1 PTH receptor induces matrix synthesis and suppresses maturation of chondrocytes. We report that the PTH receptor is up-regulated in articular chondrocytes after meniscal injury and in osteoarthritis in humans and in a mouse model of injury-induced knee osteoarthritis. To test whether recombinant human PTH(1-34) (teriparatide) would inhibit aberrant chondrocyte maturation and associated articular cartilage degeneration, we administered systemic teriparatide (Forteo), a Food and Drug Administration-approved treatment for osteoporosis, either immediately after or 8 weeks after meniscal/ligamentous injury in mice. Knee joints were harvested at 4, 8, or 12 weeks after injury to examine the effects of teriparatide on cartilage degeneration and articular chondrocyte maturation. Microcomputed tomography revealed increased bone volume within joints from teriparatide-treated mice compared to saline-treated control animals. Immediate systemic administration of teriparatide increased proteoglycan content and inhibited articular cartilage degeneration, whereas delayed treatment beginning 8 weeks after injury induced a regenerative effect. The chondroprotective and chondroregenerative effects of teriparatide correlated with decreased expression of type X collagen, RUNX2 (runt-related transcription factor 2), matrix metalloproteinase 13, and the carboxyl-terminal aggrecan cleavage product NITEGE. These preclinical findings provide proof of concept that Forteo may be useful for decelerating cartilage degeneration and inducing matrix regeneration in patients with osteoarthritis.

Unique angiogenic and vasculogenic properties of renal cell carcinoma in a xenograft model of bone metastasis are associated with high levels of vegf-a and decreased ang-1 expression

Management of various tumor metastases to bone has dramatically improved, but this is not so for renal cell carcinoma (RCC), which is a difficult surgical problem due to its great vascularity. Furthermore, the unique mechanisms that mediate RCC vasculogenesis in bone remain unknown. To understand this process we developed a xenograft model that recapitulates highly vascular RCC versus less vascular tumors that metastasize to bone. Human tumor cell lines of RCC (786-O), prostate cancer (PC3), lung cancer (A549), breast cancer (MDA-MB231), and melanoma (A375) were transduced with firefly luciferase (Luc), injected into the tibiae of nude mice, and differences in growth, osteolysis, and vascularity were assessed by longitudinal bioluminescent imaging, micro-CT for measurement of calcified tissues and vascularity and histology. The results showed that while RCC-Luc has reduced growth and osteolytic potential versus the other tumor lines, it displayed a significant increase in vascular volume (p < 0.05). This expansion was due to 3- and 5-fold increases in small and large vessel numbers respectively. In vitro gene expression profiling revealed that RCC-Luc expresses significantly (p < 0.05) more vegf-a (10-fold) and 20- to 30-fold less ang-1 versus the other lines. These data demonstrate the utility of this model to study the unique vasculogenic properties of RCC bone metastases.

High-fat diet accelerates progression of osteoarthritis after meniscal/ligamentous injury

Introduction

Increasing obesity and type 2 diabetes, in part due to the high-fat (HF) Western diet, parallels an increased incidence of osteoarthritis (OA). This study was undertaken to establish a causal relation between the HF diet and accelerated OA progression in a mouse model and to determine the relative roles of weight gain and metabolic dysregulation in this progression.

Methods

Five-week-old C57BL/6 mice were placed on HF (60% kcal) or low-fat (lean, 10% kcal) diets for 8 or 12 weeks before transecting the medial collateral ligament and excising a segment of the medial meniscus of the knee to initiate OA. One group was switched from lean to HF diet at the time of surgery.

Results

Body weight of mice on the HF diet peaked at 45.9 ± 2.1 g compared with 29.9 ± 1.8 g for lean diets, with only those on the HF becoming diabetic. Severity of OA was greater in HF mice, evidenced by the Osteoarthritis Research Society International (OARSI) histopathology initiative scoring method for mice and articular cartilage thickness and area. To assess the importance of weight gain, short- and long-term HF diets were compared with the lean diet. Short- and long-term HF groups outweighed lean controls by 6.2 g and 20.5 g, respectively. Both HF groups became diabetic, and OA progression, evidenced by increased OARSI score, decreased cartilage thickness, and increased osteophyte diameter, was comparably accelerated relative to those of lean controls.

Conclusions

These results demonstrate that the HF diet accelerates progression of OA in a type 2 diabetic mouse model without correlation to weight gain, suggesting that metabolic dysregulation is a comorbid factor in OA-related cartilage degeneration.

Establishment of an index with increased sensitivity for assessing murine arthritis

The goals of our study were to establish quantitative outcomes for assessing murine knee arthritis and develop an Arthritis Index that incorporates multiple outcomes into a single calculation that provides enhanced sensitivity. Using an accepted model of meniscal/ligamentous injury (MLI)-induced osteoarthritis (OA), we assessed mouse knee arthritis using several approaches. Histology-based methods were performed to visualize joint tissues including articular cartilage and subchondral bone. Accepted histologic scoring methods and histomorphometry were performed to grade cartilage degeneration and determine articular cartilage area, respectively. MicroCT was used to visualize and quantify the bony structures of the joint including osteophytes and joint bone volume. A statistical algorithm was then developed that combined histologic scores and cartilage areas into a single Arthritis Index. MLI induced progressive, OA-like articular cartilage degeneration characterized by increasing (worsening) histologic score and decreasing cartilage area. MicroCT revealed osteophytes and increased joint bone volume between the femoral and tibial physes following MLI. Lastly, an Arthritis Index calculation was established, which incorporated histologic scoring and cartilage area. The Arthritis Index provided enhanced quantitative sensitivity in assessing the level of joint degeneration compared to either histologic scoring or cartilage area determination alone; when using the Index, between 29% and 43% fewer samples are needed to establish statistical significance in studies of murine arthritis. Arthritis in the mouse knee can be quantitatively assessed by histologic scoring, measuring cartilage area, and determining joint bone volume. Enhanced sensitivity can be achieved by performing the Arthritis Index calculation, a novel method for quantitatively assessing mouse knee arthritis.

The orally bioavailable met inhibitor PF-2341066 inhibits osteosarcoma growth and osteolysis/matrix production in a xenograft model

Osteosarcoma (OS) is the most common primary bone tumor in children and adolescents. Ninety percent of patients who present with metastatic and 30% to 40% of patients with nonmetastatic disease experience relapse, creating an urgent need for novel therapeutic strategies. The Met receptor tyrosine kinase and its ligand, hepatocyte growth factor (HGF), are important for mitosis, motility, and cell survival. Upregulation of Met/HGF signaling via receptor overexpression, amplification, or mutation drives the proliferation, invasiveness, and metastasis of a variety of cancer cells, including OS, prompting the development of Met/HGF inhibitors. OS cells depend on Met overexpression because introduction of dominant-negative Met inhibits in vivo tumorigenicity. Despite the importance of Met/HGF signaling in the development and maintenance of OS, the potential efficacy of pharmacologic Met inhibition in OS has been addressed only in in vitro studies. PF-2341066 is an orally bioavailable, selective ATP-competitive Met inhibitor that showed promising results recently in a phase I clinical trial in non-small cell lung cancer (NSCLC) patients. We tested the ability of PF-2341066 to inhibit malignant properties of osteosarcoma cells in vitro and orthotopic xenograft growth in vivo. In vitro, PF-2341066 inhibited osteosarcoma behavior associated with primary tumor growth (eg, proliferation and survival) as well as metastasis (eg, invasion and clonogenicity). In nude mice treated with PF-2341066 via oral gavage, the growth and associated osteolysis and extracortical bone matrix formation of osteosarcoma xenografts were inhibited by PF-2341066. PF-2341066 may represent an effective new systemic therapy for localized and potentially disseminated osteosarcoma.

The histone deacetylase inhibitor vorinostat selectively sensitizes fibrosarcoma cells to chemotherapy

Soft tissue sarcoma (STS) is a rare malignancy that is generally resistant to chemotherapy. We investigated the ability of the histone deacetylase inhibitor vorinostat to sensitize STS cells versus normal fibroblasts to chemotherapy. Fibrosarcoma, leiomyosarcoma, and liposarcoma cells and normal fibroblasts were treated with vorinostat to determine effects on proliferation and basal apoptosis as measured by total cell number and cleaved caspase 3 staining. Effects on histone deacetylases (HDAC) activity were confirmed by Western blotting for acetylated histone H3. A clinically relevant dose of vorinostat that had no effect on basal apoptosis was selected to examine altered sensitivity to doxorubicin. The effects of vorinostat, doxorubicin, or the combination on fibrosarcoma growth in vivo were determined in a xenograft model. Tumor volume was measured biweekly and HDAC activity and cell death were assessed by immunohistochemical analysis of acetylated histone H3, cleaved caspase 3, and TUNEL staining. Vorinostat inhibited proliferation and induced histone acetylation without affecting basal apoptosis levels. Combined treatment with vorinostat and doxorubicin synergistically induced apoptosis in vitro in fibrosarcoma but not leiomyosarcoma, liposarcoma, or normal fibroblasts. In nude mice, the combination of vorinostat and doxorubicin inhibited fibrosarcoma xenograft growth further than either agent alone. Cell death, as measured by cleaved caspase 3 and TUNEL staining, was greatest in xenografts from mice treated with vorinostat and doxorubicin. Vorinostat inhibits growth and induces chemosensitivity in fibrosarcoma cells in vitro and in vivo, suggesting that the combination of vorinostat and chemotherapy may represent a novel treatment option for this STS subtype. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:623-632, 2011.

Aberrant hypertrophy in Smad3-deficient murine chondrocytes is rescued by restoring transforming growth factor beta-activated kinase 1/activating transcription factor 2 signaling: a potential clinical implication for osteoarthritis

OBJECTIVE

To investigate the biologic significance of Smad3 in the progression of osteoarthritis (OA), the crosstalk between Smad3 and activating transcription factor 2 (ATF-2) in the transforming growth factor beta (TGFbeta) signaling pathway, and the effects of ATF-2 overexpression and p38 activation in chondrocyte differentiation.

METHODS

Joint disease in Smad3-knockout (Smad3(-/-)) mice was examined by microfocal computed tomography and histologic analysis. Numerous in vitro methods including immunostaining, real-time polymerase chain reaction, Western blotting, an ATF-2 DNA-binding assay, and a p38 kinase activity assay were used to study the various signaling responses and protein interactions underlying the altered chondrocyte phenotype in Smad3(-/-) mice.

RESULTS

In Smad3(-/-) mice, an end-stage OA phenotype gradually developed. TGFbeta-activated kinase 1 (TAK1)/ATF-2 signaling was disrupted in Smad3(-/-) mouse chondrocytes at the level of p38 MAP kinase (MAPK) activation, resulting in reduced ATF-2 phosphorylation and transcriptional activity. Reintroduction of Smad3 into Smad3(-/-) cells restored the normal p38 response to TGFbeta. Phosphorylated p38 formed a complex with Smad3 by binding to a portion of Smad3 containing both the MAD homology 1 and linker domains. Additionally, Smad3 inhibited the dephosphorylation of p38 by MAPK phosphatase 1 (MKP-1). Both ATF-2 overexpression and p38 activation repressed type X collagen expression in wild-type and Smad3(-/-) chondrocytes. P38 was detected in articular cartilage and perichondrium; articular and sternal chondrocytes expressed p38 isoforms alpha, beta, and gamma, but not delta.

CONCLUSION

Smad3 is involved in both the onset and progression of OA. Loss of Smad3 abrogates TAK1/ATF-2 signaling, most likely by disrupting the Smad3-phosphorylated p38 complex, thereby promoting p38 dephosphorylation and inactivation by MKP-1. ATF-2 and p38 activation inhibit chondrocyte hypertrophy. Modulation of p38 isoform activity may provide a new therapeutic approach for OA.

Induction of an osteoarthritis-like phenotype and degradation of phosphorylated Smad3 by Smurf2 in transgenic mice

OBJECTIVE

To determine whether Smurf2, an E3 ubiquitin ligase known to inhibit transforming growth factor beta (TGFbeta) signaling, is expressed in human osteoarthritic (OA) cartilage and can initiate OA in mice.

METHODS

Human OA cartilage was obtained from patients undergoing knee arthroplasty. Samples were graded histologically using the Mankin scale and were examined immunohistochemically for Smurf2 expression. A transgene driven by the collagen 2alpha1 promoter was used to overexpress Smurf2 in mice. Smurf2 overexpression in mouse sternal chondrocytes was confirmed by reverse transcription-polymerase chain reaction and Western blotting. Changes in articular cartilage area, chondrocyte number, and chondrocyte diameter were assessed histomorphometrically using OsteoMeasure software. Alterations in type X collagen and matrix metalloproteinase 13 (MMP-13) in articular chondrocytes were examined by in situ hybridization and immunohistochemistry, respectively. Joint bone phenotypes were evaluated by microfocal computed tomography. The effects of Smurf2 overexpression on TGFbeta signaling were examined using a luciferase-based reporter and immunoprecipitation/Western blotting.

RESULTS

Human OA cartilage strongly expressed Smurf2 as compared with nonarthritic human cartilage. By 8 months of age, Smurf2-transgenic mice exhibited decreased articular cartilage area, fibrillation, clefting, eburnation, subchondral sclerosis, and osteophytes. Increased expression of type X collagen and MMP-13 were also detected in articular cartilage from transgenic mice. Transgenic sternal chondrocytes showed reduced TGFbeta signaling as well as decreased expression and increased ubiquitination of pSmad3.

CONCLUSION

Smurf2 is up-regulated during OA in humans, and Smurf2-transgenic mice spontaneously develop an OA-like phenotype that correlates with decreased TGFbeta signaling and increased pSmad3 degradation. Overall, these results suggest a role of Smurf2 in the pathogenesis of OA.

Functional domain and motif analyses of androgen receptor coregulator ARA70 and its differential expression in prostate cancer

Androgen receptor (AR)-associated coregulator 70 (ARA70) was the first identified AR coregulator. However, its molecular mechanism and biological relevance to prostate cancer remain unclear. Here we show that ARA70 interacts with and promotes AR activity via the consensus FXXLF motif within the ARA70-N2 domain (amino acids 176-401). However, it does not promote AR activity via the classic LXXLL motif located at amino acids 92-96, although this classic LXXLL motif is important for ARA70 to interact with other receptors, such as PPARgamma. The molecular mechanisms by which ARA70 enhances AR transactivation involve the increase of AR expression, protein stability, and nuclear translocation. Furthermore, ARA70 protein is more frequently detected in prostate cancer specimens (91.74%) than in benign tissues (64.64%, p < 0.0001). ARA70 expression is also increased in high-grade prostate cancer tissues as well as the hormone-refractory LNCaP xenografts and prostate cancer cell lines. Because ARA70 can promote the antiandrogen hydroxyflutamide (HF)-enhanced AR transactivation, the increased ARA70 expression in hormone-refractory prostate tumors may confer the development of HF withdrawal syndrome, commonly diagnosed in patients with the later stages of prostate cancer. Because ARA70-N2 containing the AR-interacting FXXLF motif without coactivation function can suppress HF-enhanced AR transactivation in the hormone-refractory LNCaP cells, using the ARA70-N2 inhibitory peptide at the hormone refractory stage to battle the HF withdrawal syndrome may become an alternative strategy to treat prostate cancer.

Mutations in the helix 3 region of the androgen receptor abrogate ARA70 promotion of 17beta-estradiol-induced androgen receptor transactivation

The influence of estrogen on the development of the male reproductive system may be interrupted in a subset of partial androgen insensitivity syndrome (PAIS) patients. PAIS describes a wide range of male undermasculinization resulting from mutations in the androgen receptor (AR) or steroid metabolism enzymes that perturb androgen-AR regulation of male sex organ development. In this study, we are interested in determining if PAIS-derived AR mutants that respond normally to androgen have altered responses to estrogen in the presence of ARA70, a coregulator previously shown to enhance 17beta-estradiol E2-induced AR transactivation. The wild-type AR (wtAR) and two PAIS AR mutants, AR(S703G) and AR(E709K), all bind to androgen and E2 and subsequently translocate to the nucleus. Whereas ARA70 functionally interacts with the wtAR and the PAIS AR mutants in response to androgen, E2 only promotes the functional interaction between ARA70 and the wtAR but not the PAIS AR mutants. ARA70 increases E2 competitive binding to the wtAR in the presence of low level androgen and also retards E2 dissociation from the wtAR. ARA70 is present in both the cytoplasm and the nucleus of various mouse testicular cells during early embryogenesis day 16, at postpartum day 0 during estradiol synthesis and in the Leydig cells at postpartum day 49. ARA70 may be unable to modulate the PAIS AR mutants-E2 binding, diminishing the effect of E2 via AR during male reproductive system development in patients with such mutations. Therefore, the presence of ARA70 in the testosterone and E2-producing Leydig cells may enhance the overall activity of AR during critical stages of male sex organ development.

Suppression of androgen receptor transactivation by Pyk2 via interaction and phosphorylation of the ARA55 coregulator

The proline-rich tyrosine kinase 2 (Pyk2) was first identified as a key kinase linked to the MAP kinase and JNK signaling pathways that play important roles in cell growth and adhesion. The linkage between Pyk2 and the androgen receptor (AR), an important transcription factor in prostate cancer progression, however, remains unclear. Here we report that using the full-length androgen receptor-associated protein, ARA55, coregulator as bait, we were able to isolate an ARA55-interacting protein, Pyk2, and demonstrated that Pyk2 could repress AR transactivation via inactivation of ARA55. This inactivation may result from the direct phosphorylation of ARA55 by Pyk2 at tyrosine 43, impairing the coactivator activity of ARA55 and/or sequestering ARA55 to reduce its interaction with AR. Our finding that Pyk2 can indirectly modulate AR function via interaction and/or phosphorylation of ARA55 not only expands the role of Pyk2 in AR-mediated prostate cancer growth but also strengthens the role of ARA55 as an AR coregulator.

Identification and characterization of androgen receptor associated coregulators in prostate cancer cells

The androgen receptor (AR) is a member of the nuclear receptor (NR) superfamily that mediates the effects of androgens on target tissues. Over the last decade, it has become apparent that NRs require accessory factors for optimal activation of target gene expression. Numerous NR coregulators have been identified, with diverse structures and potential mechanisms of coregulation, creating an increasingly complicated picture of NR action. Due to the expanding complexity of the coregulator field, this review will focus on the AR ligand-binding domain (LBD) and N-terminal interacting proteins identified by our lab. The LBD-interacting proteins ARA70, ARA55 and ARA54 were first characterized and ARA70 was found to have a relatively higher specificity for the AR in human prostate cancer DU145 cells. Characterization of the functional relationship between the AR and these coregulators indicated that ARA70 and ARA55 could enhance the androgenic effects of 17beta-estradiol (E2) and hydroxyflutamide (HF), an antiandrogen commonly used in the treatment of prostate cancer. ARA160, an AR N-terminal interacting protein also known as TATA element modulatory factor (TMF), was subsequently shown to cooperate with ARA70 in enhancing AR activity. Another AR N-terminal interacting protein, ARA24, interacted with the poly-Q tract, a region within the N-terminus of the AR linked to Kennedy's disease (X-linked spinal and bulbar muscular atrophy). More recently, our lab has identified ARA267, a SET domain containing protein, and supervillin, an F-actin binding protein, as AR coregulators. Collectively, the data from these studies indicate that these coregulators are necessary for optimal AR transactivation. Interruption of the interaction between AR and these proteins may serve as a new therapeutic target in the treatment of prostate cancer.

Functional analysis of androgen receptor N-terminal and ligand binding domain interacting coregulators in prostate cancer

Several new androgen receptor (AR) coregulators, including ARA70, ARA55, ARA54, ARA160 and ARA24, associated with the N-terminal or the ligand-binding domain (LBD) of AR, have been identified by our group. We first identified the AR-LBD coregulators ARA70, ARA55, and ARA54. Our previous reports suggest that ARA70 can enhance the androgenic activity of 17 beta-estradiol (E2) and antiandrogens toward AR. It is of interest to compare and determine if the specificity of sex hormones and antiandrogens can be modulated by different coregulators. Our results indicate that, ARA70 is the best coregulator for increasing the androgenic activity of E2. Only ARA70 and ARA55 were able to significantly increase the androgenic activity of hydroxyflutamide, the active metabolite of a widely-used antiandrogen for the treatment of prostate cancer. Furthermore, our results suggest that among the LBD coregulators, ARA70 has a relatively high specificity for AR in the human prostate cancer cell line DU145. Together, our data suggest that the androgenic activity of some sex hormones and antiandrogens can be modulated by selective AR coactivators. In addition to the AR-LBD associated proteins, ARA24 and ARA160 have been identified as AR coregulators, interacting with the AR N-terminal instead of the LBD. Functional analysis revealed that the AR N-terminal coregulator ARA160 could cooperate with the AR LBD-associated coregulator ARA70. Our data indicate that ARA24 could also interact with AR, and that this binding is decreased by an expanding poly-glutamine (Q) length within AR. The length of the poly-Q stretch in the AR N-terminal domain is inversely correlated with the transcriptional activity of AR. Our data suggest that optimal AR transactivation may require interaction of AR with AR coregulators. The identification of factors or peptides that can interrupt androgen-mediated AR-ARA interactions may be useful in the development of better antiandrogens for treating androgen-related diseases, such as prostate cancer.

Localization of the tandem pore domain K+ channel TASK-1 in the rat central nervous system

Recently, a new family of potassium channels with two pore domains in tandem and four transmembrane segments has been identified. Seven functional mammalian channels have been reported at this time. These channels give rise to baseline potassium currents because they are not gated by voltage and exhibit spontaneous activity at all membrane potentials. Although the physiological role of these ion channels has yet to be determined, three mammalian members of this family (TREK-1, TASK-1, TASK-2) are activated by volatile anesthetics and may therefore contribute to the central nervous system (CNS) depression produced by volatile anesthetics. In this study we used northern blot analysis and immunohistochemical localization to determine the expression of TASK-1 subunits in the CNS. TASK-1 immunoreactivity was prominently found in astrocytes of the hippocampus, in the median eminence, in the choroid plexus, and the granular layer, Purkinje cell layer, and molecular layer of the cerebellum. In the spinal cord, strong TASK-I immunoreactivity was seen in ependymal cells lining the central canal and in white matter. These findings suggest a role for the TASK-1 channel in the production of cerebrospinal fluid and function of hypothalamic neurosecretory cells.