Downregulation of SOX2 by inhibition of Usp9X induces apoptosis in melanoma

Melanoma tumors driven by BRAF mutations often do not respond to BRAF/MEK/ERK pathway inhibitors currently used in treatment. One documented mechanism of resistance is upregulation of SOX2, a transcription factor that is essential for tumor growth and expansion, particularly in melanoma tumors with BRAF mutations. Targeting transcription factors pharmacologically has been elusive for drug developers, limiting treatment options. Here we show that ubiquitin-specific peptidase 9, X-linked (Usp9x), a deubiquitinase (DUB) enzyme controls SOX2 levels in melanoma. Usp9x knockdown in melanoma increased SOX2 ubiquitination, leading to its depletion, and enhanced apoptotic effects of BRAF inhibitor and MEK inhibitors. Primary metastatic melanoma samples demonstrated moderately elevated Usp9x and SOX2 protein expression compared to tumors without metastatic potential. Usp9x knockdown, as well as inhibition with DUB inhibitor, G9, blocked SOX2 expression, suppressed in vitro colony growth, and induced apoptosis of BRAF-mutant melanoma cells. Combined treatment with Usp9x and mutant BRAF inhibitors fully suppressed melanoma growth in vivo. Our data demonstrate a novel mechanism for targeting the transcription factor SOX2, leveraging Usp9x inhibition. Thus, development of DUB inhibitors may add to the limited repertoire of current melanoma treatments.

SETDB1 mediated histone H3 lysine 9 methylation suppresses MLL-fusion target expression and leukemic transformation

Epigenetic regulators play a critical role in normal and malignant hematopoiesis. Deregulation, including epigenetic deregulation, of the HOXA gene cluster drives transformation of about 50% of acute myeloid leukemia. We recently showed that the Histone 3 Lysine 9 methyltransferase SETDB1 negatively regulates the expression of the pro-leukemic genes Hoxa9 and its cofactor Meis1 through deposition of promoter H3K9 trimethylation in MLL-AF9 leukemia cells. Here, we investigated the biological impact of altered SETDB1 expression and changes in H3K9 methylation on acute myeloid leukemia. We demonstrate that SETDB1 expression is correlated to disease status and overall survival in acute myeloid leukemia patients. We recapitulated these findings in mice, where high expression of SETDB1 delayed MLL-AF9 mediated disease progression by promoting differentiation of leukemia cells. We also explored the biological impact of treating normal and malignant hematopoietic cells with an H3K9 methyltransferase inhibitor, UNC0638. While myeloid leukemia cells demonstrate cytotoxicity to UNC0638 treatment, normal bone marrow cells exhibit an expansion of cKit+ hematopoietic stem and progenitor cells. Consistent with these data, we show that bone marrow treated with UNC0638 is more amenable to transformation by MLL-AF9. Next generation sequencing of leukemia cells shows that high expression of SETDB1 induces repressive changes to the promoter epigenome and downregulation of genes linked with acute myeloid leukemia, including Dock1 and the MLL-AF9 target genes Hoxa9, Six1, and others. These data reveal novel targets of SETDB1 in leukemia that point to a role for SETDB1 in negatively regulating pro-leukemic target genes and suppressing acute myeloid leukemia.

Selective inhibition of Ph-positive ALL cell growth through kinase-dependent and -independent effects by CDK6-specific PROTACs

Expression of the cell cycle regulatory gene CDK6 is required for Philadelphia-positive (Ph+) acute lymphoblastic leukemia (ALL) cell growth, whereas expression of the closely related CDK4 protein is dispensable. Moreover, CDK6 silencing is more effective than treatment with the dual CDK4/6 inhibitor palbociclib in suppressing Ph+ ALL in mice, suggesting that the growth-promoting effects of CDK6 are, in part, kinase-independent in Ph+ ALL. Accordingly, we developed CDK4/6-targeted proteolysis-targeting chimeras (PROTACs) that inhibit CDK6 enzymatic activity in vitro, promote the rapid and preferential degradation of CDK6 over CDK4 in Ph+ ALL cells, and markedly suppress S-phase cells concomitant with inhibition of CDK6-regulated phospho-RB and FOXM1 expression. No such effects were observed in CD34+ normal hematopoietic progenitors, although CDK6 was efficiently degraded. Treatment with the CDK6-degrading PROTAC YX-2-107 markedly suppressed leukemia burden in mice injected with de novo or tyrosine kinase inhibitor-resistant primary Ph+ ALL cells, and this effect was comparable or superior to that of the CDK4/6 enzymatic inhibitor palbociclib. These studies provide "proof of principle" that targeting CDK6 with PROTACs that inhibit its enzymatic activity and promote its degradation represents an effective strategy to exploit the "CDK6 dependence" of Ph+ ALL and, perhaps, of other hematologic malignancies. Moreover, they suggest that treatment of Ph+ ALL with CDK6-selective PROTACs would spare a high proportion of normal hematopoietic progenitors, preventing the neutropenia induced by treatment with dual CDK4/6 inhibitors.

Tumor necrosis factor related apoptosis inducing ligand (TRAIL) regulates deubiquitinase USP5 in tumor cells

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) pathway has emerged as a cancer therapeutic target. However, clinical trials have proven that most human cancers are resistant to TRAIL. We show that exposure to recombinant TRAIL resulted in the accumulation of ubiquitinated proteins and free ubiquitin polymers, suggesting a link between TRAIL and the ubiquitin (Ub)-proteasome pathway. TRAIL treatment in cancer cells reduced the activity and cleavage of USP5, a deubiquitinase (DUB) previously shown to target unanchored Ub polymers and regulate p53-mediated transcription. TRAIL was effective in suppressing USP5 activity and cleavage in TRAIL-sensitive cells but not resistant cells. Knockdown of USP5 in TRAIL-resistant cells demonstrated that USP5 controls apoptotic responsiveness to TRAIL. USP5 cleavage and ubiquitination were blocked by caspase-8 specific inhibitors. A small-molecule USP5/9× inhibitor (G9) combined with TRAIL enhanced apoptosis and blocked colony growth in highly TRAIL-resistant cell lines. Finally, USP5 protein levels and activity were found to be frequently deregulated in TRAIL-resistant cells. Together, we conclude that activated TRAIL enhances USP5 activity and induces apoptosis in TRAIL-sensitive and -resistant cells. We also suggest that USP5 inhibition may be effective in inducing apoptotic thresholds to enhance responsiveness to TRAIL.

Follicular lymphoma-associated mutations in vacuolar ATPase ATP6V1B2 activate autophagic flux and mTOR

The discovery of recurrent mutations in subunits of the vacuolar-type H+-translocating ATPase (v-ATPase) in follicular lymphoma (FL) highlights a role for the amino acid- and energy-sensing pathway to mTOR in the pathogenesis of this disease. Here, through the use of complementary experimental approaches involving mammalian cells and Saccharomyces cerevisiae, we have demonstrated that mutations in the human v-ATPase subunit ATP6V1B2 (also known as Vma2 in yeast) activate autophagic flux and maintain mTOR/TOR in an active state. Engineered lymphoma cell lines and primary FL B cells carrying mutated ATP6V1B2 demonstrated a remarkable ability to survive low leucine concentrations. The treatment of primary FL B cells with inhibitors of autophagy uncovered an addiction for survival for FL B cells harboring ATP6V1B2 mutations. These data support the idea of mutational activation of autophagic flux by recurrent hotspot mutations in ATP6V1B2 as an adaptive mechanism in FL pathogenesis and as a possible new therapeutically targetable pathway.

Leukemia inhibitory factor functions in parallel with interleukin-6 to promote ovarian cancer growth

Ovarian carcinoma-associated mesenchymal stem cells (CA-MSC) produce not only high levels of IL6 but also the related cytokine leukemia inhibitory factor (LIF). Interleukin 6 (IL6) mediated activation of STAT3 is implicated as a critical therapeutic target for cancer therapy. Less is known about the role of LIF, which can similarly activate STAT3, in ovarian cancer. We therefore sought to evaluate the tumorigenic effects of CA-MSC paracrine LIF signaling and the redundancy of IL6 and LIF in activating ovarian cancer STAT3 mediated cancer growth. As expected, we found that both IL6 and LIF induce STAT3 phosphorylation in tumor cells. In addition, both IL6 and LIF increased the percentage of ALDH+ ovarian cancer stem-like cells (CSC). Supporting redundancy of function by the two cytokines, CA-MSC induced STAT3 phosphorylation and increased cancer cell ‘stemness’. This effect was not inhibited by LIF or IL6 blocking antibodies alone, but was prevented by dual IL6/LIF blockade or JAK2 inhibition. Similarly, small hairpin RNA (shRNA)-mediated reduction of IL6 or LIF in CA-MSC partially decreased but could not completely abrograte the ability of CA-MSC to induce STAT3 phosphorylation and stemness. Importantly, the in vivo pro-tumorigenic effect of CA-MSC is abrogated by dual blockade with the JAK2 inhibitor ruxolitinib to a much greater extent than treatment with anti-IL6 or anti-LIF antibody alone. Ruxolitinib treatment also improves survival in the immunocompetent ovarian cancer mouse model system with ID8 tumor cells plus MSC. Ruxolitinib-treated tumors in both the immunocompromised and immunocompetent animal models demonstrate decreased phospho-STAT3, indicating on-target activity. In conclusion, CA-MSC activate ovarian cancer cell STAT3 signaling via IL6 and LIF and increase tumorigenesis cancer stemness. This functional redundancy suggests that therapeutic targeting of a single cytokine may be less effective than strategies such as dual inhibitor therapy or targeting shared downstream factors of the JAK/STAT pathway.

Targeting STAT5 or STAT5-Regulated Pathways Suppresses Leukemogenesis of Ph+ Acute Lymphoblastic Leukemia

Combining standard cytotoxic chemotherapy with BCR-ABL1 tyrosine kinase inhibitors (TKI) has greatly improved the upfront treatment of patients with Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL). However, due to the development of drug resistance through both BCR-ABL1-dependent and -independent mechanisms, prognosis remains poor. The STAT5 transcription factor is activated by BCR-ABL1 and by JAK2-dependent cytokine signaling; therefore, inhibiting its activity could address both mechanisms of resistance in Ph+ ALL. We show here that genetic and pharmacologic inhibition of STAT5 activity suppresses cell growth, induces apoptosis, and inhibits leukemogenesis of Ph+ cell lines and patient-derived newly diagnosed and relapsed/TKI-resistant Ph+ ALL cells ex vivo and in mouse models. STAT5 silencing decreased expression of the growth-promoting PIM-1 kinase, the apoptosis inhibitors MCL1 and BCL2, and increased expression of proapoptotic BIM protein. The resulting apoptosis of STAT5-silenced Ph+ BV173 cells was rescued by silencing of BIM or restoration of BCL2 expression. Treatment of Ph+ ALL cells, including samples from relapsed/refractory patients, with the PIM kinase inhibitor AZD1208 and/or the BCL2 family antagonist Sabutoclax markedly suppressed cell growth and leukemogenesis ex vivo and in mice. Together, these studies indicate that targeting STAT5 or STAT5-regulated pathways may provide a new approach for therapy development in Ph+ ALL, especially the relapsed/TKI-resistant disease.Significance: Suppression of STAT5 by BCL2 and PIM kinase inhibitors reduces leukemia burden in mice and constitutes a new potential therapeutic approach against Ph+ ALL, especially in tyrosine kinase inhibitor-resistant disease. Cancer Res; 78(20); 5793-807. ©2018 AACR.

Targeting CDK6 and BCL2 Exploits the "MYB Addiction" of Ph+ Acute Lymphoblastic Leukemia

Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph⁺ ALL) is currently treated with BCR-ABL1 tyrosine kinase inhibitors (TKI) in combination with chemotherapy. However, most patients develop resistance to TKI through BCR-ABL1-dependent and -independent mechanisms. Newly developed TKI can target Ph⁺ ALL cells with BCR-ABL1-dependent resistance; however, overcoming BCR-ABL1-independent mechanisms of resistance remains challenging because transcription factors, which are difficult to inhibit, are often involved. We show here that (i) the growth of Ph⁺ ALL cell lines and primary cells is highly dependent on MYB-mediated transcriptional upregulation of CDK6, cyclin D3, and BCL2, and (ii) restoring their expression in MYB-silenced Ph⁺ ALL cells rescues their impaired proliferation and survival. Levels of MYB and CDK6 were highly correlated in adult Ph⁺ ALL (P = 0.00008). Moreover, Ph⁺ ALL cells exhibited a specific requirement for CDK6 but not CDK4 expression, most likely because, in these cells, CDK6 was predominantly localized in the nucleus, whereas CDK4 was almost exclusively cytoplasmic. Consistent with their essential role in Ph⁺ ALL, pharmacologic inhibition of CDK6 and BCL2 markedly suppressed proliferation, colony formation, and survival of Ph⁺ ALL cells ex vivo and in mice. In summary, these findings provide a proof-of-principle, rational strategy to target the MYB "addiction" of Ph⁺ ALL.Significance: MYB blockade can suppress Philadelphia chromosome-positive leukemia in mice, suggesting that this therapeutic strategy may be useful in patients who develop resistance to imatinib and other TKIs used to treat this disease. Cancer Res; 78(4); 1097-109. ©2017 AACR.

Abstract 5083: A novel and highly efficacious small-molecule degrader of BET-BRD proteins for the treatment of acute leukemia

The bromodomain and extra-terminal domain (BET-BRD) family of lysine acetylation readers comprises BRD2, BRD3, BRD4, and BRDT that contain two conserved N-terminal bromodomains (BD1 and BD2) and a long C-terminal region containing the extraterminal (ET) protein-protein interaction domain. These proteins have key roles in the assembly of transcriptional regulatory complexes containing RNA polymerase II. BET-BRDs are new therapeutic targets for cancer treatment and several small-molecule BET-BRD inhibitors are currently in clinical development for a diverse set of cancers including leukemia. Based on the proteolysis targeting chimera (PROTAC) concept, we have developed novel and highly potent BET degraders, ZBC246 and ZBC260, with exceptional selectivity based upon a new class of BET inhibitor, ZBC11. ZBC260 effectively degrades all BET-BRD proteins at concentrations as low as 30 pM within a few hours of treatment in the RS4;11 leukemia cell line and achieves IC50 values of 50 pM in inhibition of RS4;11 cell growth. ZBC260 was tested in a panel of 10 acute leukemia cell lines generating IC50s ranging from 20 pM to 1 nM in 4-days cell growth inhibition assays. In contrast to the cytostatic effect observed with BET-BRD inhibition, degradation of BET-BRDs by ZBC246 and ZBC260 induced robust apoptosis demonstrating a differential biology between BET-BRD inhibitors and BET-BRD degraders. Significantly, ZBC260 induces rapid regression of RS4;11 xenograft tumors without overt signs of toxicity in mice. More importantly, treatment of leukemia cells obtained from 10 patients with ZBC260 demonstrated efficient degradation of BET-BRDs within 5 h at 0.3 nM, while treatment with the inhibitor (300 nM) induced up-regulation of BET-BRDs. Treatment of patients’ peripheral blasts with ZBC260 at 1 to 10 nM induced remarkable levels of apoptosis within 24 h, even in relapsed and refractory patient samples. In conclusion, ZBC260 represents a highly potent and efficacious BET-BRD degrader undergoing extensive preclinical evaluation for the treatment of acute leukemias.

Citation Format: Ester Fernandez-Salas, Zhuo Chen, Mei Lin, Bing Zhou, Donna McEachern, Sally Przybranowski, Karson Kump, Luke F. Peterson, Malathi Kandarpa, Jiantao Hu, Fuming Xu, Liu Liu, Longchuan Bai, Bo Wen, Duxin Sun, Moshe Talpaz, Shaomeng Wang. A novel and highly efficacious small-molecule degrader of BET-BRD proteins for the treatment of acute leukemia [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 5083. doi:10.1158/1538-7445.AM2017-5083

Usp9x regulates Ets-1 ubiquitination and stability to control NRAS expression and tumorigenicity in melanoma

ETS transcription factors are commonly deregulated in cancer by chromosomal translocation, overexpression or post-translational modification to induce gene expression programs essential in tumorigenicity. Targeted destruction of these proteins may have therapeutic impact. Here we report that Ets-1 destruction is regulated by the deubiquitinating enzyme, Usp9x, and has major impact on the tumorigenic program of metastatic melanoma. Ets-1 deubiquitination blocks its proteasomal destruction and enhances tumorigenicity, which could be reversed by Usp9x knockdown or inhibition. Usp9x and Ets-1 levels are coincidently elevated in melanoma with highest levels detected in metastatic tumours versus normal skin or benign skin lesions. Notably, Ets-1 is induced by BRAF or MEK kinase inhibition, resulting in increased NRAS expression, which could be blocked by inactivation of Usp9x and therapeutic combination of Usp9x and MEK inhibitor fully suppressed melanoma growth. Thus, Usp9x modulates the Ets-1/NRAS regulatory network and may have biologic and therapeutic implications.

Induction of p53 suppresses chronic myeloid leukemia

Chronic myeloid leukemia (CML) is characterized by the chromosomal translocation 9;22, known as the Philadelphia chromosome (Ph), which produces the BCR-ABL fusion tyrosine kinase. Although well-managed by BCR-ABL tyrosine kinase inhibitors (TKIs), treatment fails to eliminate Ph + primitive progenitors, and cessation of therapy frequently results in relapse. The p53 protein is an important regulator of cell cycle and apoptosis. The small molecules MI-219 target the interaction between p53 and its negative regulator HDM2, leading to its stabilization and activation. We show that treatment with MI-219 reduced the number of CML cells in both in vitro and in vivo settings but not that of normal primitive progenitors, and activated different gene signatures in CML potentially explaining the differential impact of this agent on each population. Our data suggest that a p53-activating agent may be an effective approach in the management and potential operational cure of CML.

Recurrent Mutations in the MTOR Regulator RRAGC in Follicular Lymphoma

PURPOSE

This study was performed to further our understanding of the biological and genetic basis of follicular lymphoma and to identify potential novel therapy targets.

EXPERIMENTAL DESIGN

We analyzed previously generated whole exome sequencing data of 23 follicular lymphoma cases and one transformed follicular lymphoma case and expanded findings to a combined total of 125 follicular lymphoma/3 transformed follicular lymphoma. We modeled the three-dimensional location of RRAGC-associated hotspot mutations. We performed functional studies on novel RRAGC mutants in stable retrovirally transduced HEK293T cells, stable lentivirally transduced lymphoma cell lines, and in Saccharomyces cerevisiae RESULTS: We report recurrent mutations, including multiple amino acid hotspots, in the small G-protein RRAGC, which is part of a protein complex that signals intracellular amino acid concentrations to MTOR, in 9.4% of follicular lymphoma cases. Mutations in RRAGC distinctly clustered on one protein surface area surrounding the GTP/GDP-binding sites. Mutated RRAGC proteins demonstrated increased binding to RPTOR (raptor) and substantially decreased interactions with the product of the tumor suppressor gene FLCN (folliculin). In stable retrovirally transfected 293T cells, cultured in the presence or absence of leucine, multiple RRAGC mutations demonstrated elevated MTOR activation as evidenced by increased RPS6KB/S6-kinase phosphorylation. Similar activation phenotypes were uncovered in yeast engineered to express mutations in the RRAGC homolog Gtr2 and in multiple lymphoma cell lines expressing HA-tagged RRAGC-mutant proteins.

CONCLUSIONS

Our discovery of activating mutations in RRAGC in approximately 10% of follicular lymphoma provides the mechanistic rationale to study mutational MTOR activation and MTOR inhibition as a potential novel actionable therapeutic target in follicular lymphoma. Clin Cancer Res; 22(21); 5383-93. ©2016 AACR.

CDKN2A-independent role of BMI1 in promoting growth and survival of Ph+ acute lymphoblastic leukemia

BMI1 is a key component of the PRC1 complex (polycomb repressive complex-1) required for maintenance of normal and cancer stem cells. Its aberrant expression is detected in chronic myeloid leukemia and Ph+ acute lymphoblastic leukemia (ALL), but no data exist on BMI1 requirement in ALL cells.

We show here that BMI1 expression is important for proliferation and survival of Ph+ ALL cells and for leukemogenesis of Ph+ cells in vivo.

Levels of BIM, interferon-α (IFNα)-regulated genes, and E2F7 were upregulated in BMI1-silenced cells, suggesting that repressing their expression is important for BMI1 biological effects. Consistent with this hypothesis, we found that: i) downregulation of BIM or E2F7 abrogated apoptosis or rescued, in part, the reduced proliferation and colony formation of BMI1 silenced BV173 cells; ii) BIM/E2F7-double silencing further enhanced colony formation and in vivo leukemogenesis of BMI1-silenced cells; iii) overexpression of BIM and E2F7 mimicked the effect of BMI1 silencing in BV173 and SUP-B15 cells and iv) treatment with IFNα suppressed proliferation and colony formation of Ph+ ALL cells.

These studies indicate that the growth-promoting effects of BMI1 in Ph+ ALL cells depend on suppression of multiple pathways and support the use of IFNα in the therapy of Ph+ ALL.

Abstract 3621: Deubiquitination of AXIN1 by USP9X promotes apoptosis in melanoma in response to BRAF or MEK inhibition

The Wnt/β-catenin pathway is important in development, transformation and self-renewal of various tissues and tumors. In contrast, Wnt/β-catenin signaling appears to play a paradoxical role in melanoma where its activation is anti-oncogenic and a marker of good prognosis. Previous studies have shown that activation of the NRAS/BRAF/MEK pathway suppresses Wnt/β-catenin signaling and reduces apoptotic sensitivity to BRAF or MEK inhibitors in melanoma. MEK pathway activation stabilized AXIN1, a Wnt/β-catenin inhibitor, in some melanoma cell lines through a proteasome-dependent process and co-treatment with Wnt3A and BRAF/MEK kinase inhibitors resulted in a reduction of AXIN1 and full activation of apoptosis. Further, AXIN1 knockdown sensitized BRAF/MEK inhibitor insensitive cells to kinase inhibition, providing a prominent role for AXIN1 in determining melanoma cell apoptotic responsiveness and exposing a potential mechanism for improving kinase inhibitor clinical activity. While AXIN1 protein levels appear to be regulated by ubiquitination, the enzymes involved in control of its ubiquitination or deubiquitination are not fully defined. Here we show that ubiquitin-specific peptidase 9, X-linked (USP9X), a deubiquitinating enzyme whose expression is elevated in melanoma, binds and deubiquitinates AXIN1. USP9X knockdown resulted in increased ubiquitination and proteasome-mediated depletion of AXIN1 (but not AXIN2), resulting in a reduction in AXIN1 cellular half-life. USP9X knockdown elevated β-catenin response genes (>2-fold) in melanoma cells treated with Wnt3A. USP9X depletion also increased apoptotic responsiveness to Wnt3A or BRAF/MEK inhibitor and overcame BRAF inhibitor resistance in A375R cells. In contrast, USP34 which was previously shown to regulate AXIN1 (and AXIN2) deubiquitination, did not alter AXIN1 levels or apoptotic responsiveness in melanoma. A previously identified small molecule USP9X inhibitor (EOAI3402143 or G9) replicated the effects of USP9X knockdown on AXIN1 depletion in vitro and in vivo, suppressed melanoma tumor growth in animals and fully blocked in vivo tumor growth when combined with BRAF kinase inhibitor. Thus, we identify USP9X as a potential therapeutic target in melanoma and established G9 as a lead compound for the development of AXIN1 depleting agents that may add to the targeted therapies already used in the treatment of melanoma.

Note: This abstract was not presented at the meeting.

Citation Format: Harish Potu, Luke F. Peterson, Malathi Kandarpa, Eric Fearon, Moshe Talpaz, Nicholas J. Donato. Deubiquitination of AXIN1 by USP9X promotes apoptosis in melanoma in response to BRAF or MEK inhibition. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3621. doi:10.1158/1538-7445.AM2015-3621

Usp5 links suppression of p53 and FAS levels in melanoma to the BRAF pathway

Usp5 is a deubiquitinase (DUB) previously shown to regulate unanchored polyubiquitin (Ub) chains, p53 transcriptional activity and double-strand DNA repair. In BRAF mutant melanoma cells, Usp5 activity was suppressed by BRAF inhibitor (vemurafenib) in sensitive but not in acquired or intrinsically resistant cells. Usp5 knockdown overcame acquired vemurafenib resistance and sensitized BRAF and NRAS mutant melanoma cells to apoptosis initiated by MEK inhibitor, cytokines or DNA-damaging agents. Knockdown and overexpression studies demonstrated that Usp5 regulates p53 (and p73) levels and alters cell growth and cell cycle distribution associated with p21 induction. Usp5 also regulates the intrinsic apoptotic pathway by modulating p53-dependent FAS expression. A small molecule DUB inhibitor (EOAI3402143) phenocopied the FAS induction and apoptotic sensitization of Usp5 knockdown and fully blocked melanoma tumor growth in mice. Overall, our results demonstrate that BRAF activates Usp5 to suppress cell cycle checkpoint control and apoptosis by blocking p53 and FAS induction; all of which can be restored by small molecule-mediated Usp5 inhibition. These results suggest that Usp5 inhibition can provide an alternate approach in recovery of diminished p53 (or p73) function in melanoma and can add to the targeted therapies already used in the treatment of melanoma.

Combined gene expression and DNA occupancy profiling as a strategy to identify therapeutic target(s) in t(8;21) acute myeloid leukemia

Microarray technology has contributed valuable information to gene expression signatures of leukemia and other types of cancers and helped to identify biological markers and potential therapeutic targets for treating these diseases. Acute myeloid leukemia (AML) is often caused by aberrant fusion transcription factors resulting from chromosomal translocations, and the dysregulated genes detected by microarray include both direct and indirect targets of the oncogenic transcription factors. The ChIP-chip technology enables the identification of direct targets of a transcription factor based on its promoter occupancy and cellular context. Using AML1-ETO9a-induced AML as a cancer model and using a combined gene expression and promoter occupancy profiling approach, we recently identified CD45 as a direct down-regulated target of t(8;21) fusion proteins. This finding subsequently led us to discover the enhanced Janus activated kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathway, which is negatively regulated by CD45, in t(8;21) AML. This review summarizes the background of t(8;21) leukemia, structural features of the translocation fusion proteins, and the merits of combining gene discovery technologies for the identification of therapeutic targets in t(8;21) leukemia.

Abstract 2323: Mutant B-Raf-mediated activation of deubiquitinases in melanoma defines Usp5 as a potential therapeutic target

Melanoma is a lethal form of cutaneous cancer which accounts for 80% of skin cancer deaths owing to its highly metastatic behavior and few clinically effective therapies. More than 60% of melanoma patients present with mutations in B-Raf, a serine/threonine kinase that increases proliferation and survival through the constitutive activation of ERK signaling. Inhibition of mutated B-Raf with specific inhibitors like vemurafenib reduces tumor growth and extends patient survival. However, clinical responsiveness to vemurafenib is limited in most melanoma patients, prompting analysis of additional pathways that could be targeted to extend vemurafenib responsiveness or overcome resistance. Towards this goal, we examined the impact of vemurafenib on substrates or cascades activated in B-Raf mutant and wild-type melanoma cells. We were particularly interested in assessing the impact of mutant B-Raf inhibition on deubiquitinases (DUBs), which are overexpressed or activated in many tumor types. DUBs control the stability, activity and localization of multiple proteins and are emerging as therapeutic targets. We found that vemurafenib treatment or lentiviral-mediated B-Raf knockdown reduced the activity of several DUBs in B-Raf mutant melanoma cells, including Usp9x, Usp14 and Usp5. These DUBs were not affected by vemurafenib in w/t B-Raf-expressing cells. Interestingly lentiviral-mediated knockdown of Usp5, but not Usp9x, reduced melanoma growth and increased vemurafenib sensitivity whereas Usp5 overexpression suppressed vemurafenib activity. Inhibition of Usp5 activity by vemurafenib or by Usp5 shRNA KD alone had little effect on melanoma cell apoptosis. However B-Raf inhibition in Usp5 KD cells resulted in >5-fold increased melanoma cell apoptosis. Further, Usp5 KD increased accumulation of p53 and p53-related proteins as well as their transcriptional targets. Our data clearly shows that mutant B-Raf activates Usp5 to suppress apoptotic responsiveness to vemurafenib and kinase inhibition alone was not sufficient to completely suppress Usp5 activity. Silencing studies demonstrate that Usp5 inhibition will enhance cell killing in response to B-Raf inhibition in melanoma. To address that potential, we compared anti-tumor activity in mice treated with vemurafenib and a small molecule DUB inhibitor, WP1130, with activity against Usp5. Treatment with either agent alone reduced tumor growth while mice receiving both vemurafenib and WP1130 had enhanced anti-tumor responses. Together, these results suggest that mutant B-Raf activates Usp5 activity to suppress p53 induction and apoptotic responsiveness to vemurafenib. These observations also suggest that further testing and refinement of Usp5 inhibitors as an additional approach to targeted therapy for melanoma are warranted.

Citation Format: Harish Potu, Luke F. Peterson, Monique Verhaegen, Moshe Talpaz, Nicholas J. Donato. Mutant B-Raf-mediated activation of deubiquitinases in melanoma defines Usp5 as a potential therapeutic target. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2323. doi:10.1158/1538-7445.AM2013-2323

Combined gene expression and DNA occupancy profiling identifies potential therapeutic targets of t(8;21) AML

Chromosome translocation 8q22;21q22 [t(8;21)] is commonly associated with acute myeloid leukemia (AML), and the resulting AML1-ETO fusion proteins are involved in the pathogenesis of AML. To identify novel molecular and therapeutic targets, we performed combined gene expression microarray and promoter occupancy (ChIP-chip) profiling using Lin(-)/Sca1(-)/cKit(+) cells, the major leukemia cell population, from an AML mouse model induced by AML1-ETO9a (AE9a). Approximately 30% of the identified common targets of microarray and ChIP-chip assays overlap with the human t(8;21)-gene expression molecular signature. CD45, a protein tyrosine phosphatase and a negative regulator of cytokine/growth factor receptor and JAK/STAT signaling, is among those targets. Its expression is substantially down-regulated in leukemia cells. Consequently, JAK/STAT signaling is enhanced. Re-expression of CD45 suppresses JAK/STAT activation, delays leukemia development, and promotes apoptosis of t(8;21)-positive cells. This study demonstrates the benefit of combining gene expression and promoter occupancy profiling assays to identify molecular and potential therapeutic targets in human cancers and describes a previously unappreciated signaling pathway involving t(8;21) fusion proteins, CD45, and JAK/STAT, which could be a potential novel target for treating t(8;21) AML.

Chronic myeloid leukemia stem cells and developing therapies

Chronic myeloid leukemia therapy has remarkably improved with the use of frontline BCR-ABL kinase inhibitors such that newly diagnosed patients have minimal disease manifestations or progression. Effective control of disease may also set the stage for eventual 'cure' of this leukemia. However, the existence of Philadelphia chromosome-positive leukemic cells that are unaffected by BCR-ABL inhibition represents a major barrier that may delay or prevent curative therapy with the current approaches. The most commonly reported mechanism of resistance to tyrosine kinase inhibitor-based therapies involves BCR-ABL gene mutations and amplification, but these changes may not be solely responsible for disease relapse when inhibitor-based therapies are curtailed. Therefore new targets may need to be defined before significant advancement in curative therapies is possible. Emerging evidence suggests that persistence of chronic myeloid leukemia stem cells or acquisition of stem cell-like characteristics prevents complete elimination of chronic myeloid leukemia by tyrosine kinase inhibition alone. This review focuses on several recently emerging concepts regarding the existence and characteristics of chronic myeloid leukemia stem cells. Definitions based on human primary cells and animal model studies are highlighted as are the potential signaling pathways associated with disease repopulating cells. Finally, several recently defined therapeutic targets and active compounds that have emerged from stem cell studies are described. Our goal is to provide an unbiased report on the current state of discovery within the chronic myeloid leukemia stem cell field and to orient the reader to emerging therapeutic targets and strategies that may lead to elimination of this leukemia.

Deubiquitinase inhibition by small-molecule WP1130 triggers aggresome formation and tumor cell apoptosis

Recent evidence suggests that several deubiquitinases (DUB) are overexpressed or activated in tumor cells and many contribute to the transformed phenotype. Agents with DUB inhibitory activity may therefore have therapeutic value. In this study, we describe the mechanism of action of WP1130, a small molecule derived from a compound with Janus-activated kinase 2 (JAK2) kinase inhibitory activity. WP1130 induces rapid accumulation of polyubiquitinated (K48/K63-linked) proteins into juxtanuclear aggresomes, without affecting 20S proteasome activity. WP1130 acts as a partly selective DUB inhibitor, directly inhibiting DUB activity of USP9x, USP5, USP14, and UCH37, which are known to regulate survival protein stability and 26S proteasome function. WP1130-mediated inhibition of tumor-activated DUBs results in downregulation of antiapoptotic and upregulation of proapoptotic proteins, such as MCL-1 and p53. Our results show that chemical modification of a previously described JAK2 inhibitor results in the unexpected discovery of a novel DUB inhibitor with a unique antitumor mechanism.

An inhibitor-resistant mutant of Hck protects CML cells against the antiproliferative and apoptotic effects of the broad-spectrum Src family kinase inhibitor A-419259

Chronic myelogenous leukemia (CML) is driven by Bcr-Abl, a constitutively active protein-tyrosine kinase that stimulates proliferation and survival of myeloid progenitors. Global inhibition of myeloid Src family kinase (SFK) activity with the broad-spectrum pyrrolo-pyrimidine inhibitor, A-419259, blocks proliferation and induces apoptosis in CML cell lines, suggesting that transformation by Bcr-Abl requires SFK activity. However, the contribution of Hck and other individual SFKs to Bcr-Abl signaling is less clear. Here, we developed an A-419259-resistant mutant of Hck by replacing the gatekeeper residue (Thr-338; c-Src numbering) in the inhibitor-binding site with a bulkier methionine residue (Hck-T338M). This substitution reduced Hck sensitivity to A-419259 by more than 30-fold without significantly affecting kinase activity in vitro. Expression of Hck-T338M protected K-562 CML cells and Bcr-Abl-transformed TF-1 myeloid cells from the apoptotic and antiproliferative effects of A-419259. These effects correlated with persistence of Hck-T338M kinase activity in the presence of the compound, and were accompanied by sustained Erk and Stat5 activation. In contrast, control cells expressing equivalent levels of wild-type Hck retained sensitivity to the inhibitor. We also show for the first time that A-419259 induces cell-cycle arrest and apoptosis in primary CD34(+) CML cells with equal potency to imatinib. These data suggest that Hck has a nonredundant function as a key downstream signaling partner for Bcr-Abl and may represent a potential drug target in CML.

Inability of RUNX1/AML1 to breach AML1-ETO block of embryonic stem cell definitive hematopoiesis

The t(8;21)(q22:q22) translocation associated with acute myeloid leukemia fuses the AML1/RUNX1 N-terminal portion located on chromosome 21 to most of the ETO/MTG8 gene on chromosome 8. Various investigators have shown that the fusion product AML1-ETO on its own is unable to promote leukemia. Early studies using transgenic mouse models demonstrated that the direct knock-in of the fusion protein expression is embryonic lethal, similar to the AML1 knockout, suggesting that AML1-ETO has a dominant negative role over AML1. Using the embryonic stem cells generated for such studies, we show here that the presence of the fusion product AML1-ETO blocks definitive hematopoiesis in vitro as well, in both one and two step methylcellulose methods of embryonic stem cell hematopoietic differentiation. However, there is a very low occurrence of macrophage colonies, similar to the knock-in mice that display macrophages in cell cultures of yolk sac derived cells. In addition, we show that exogenous expression of AML1 is unable to bypass this AML1-ETO induced definitive hematopoietic block in these cells. This inability is not linked to an inability to reverse gene expression inhibition by AML1-ETO of the PU.1 gene associated with stem cell maintenance and myeloid differentiation. Our results suggest that AML1-ETO functions in a complex competitive manner with AML1 involving transcriptional regulation, protein-protein interactions and post-transcriptional mechanism(s) affecting early embryonic hematopoiesis and possibly leukemogenesis.

The multi-functional cellular adhesion molecule CD44 is regulated by the 8;21 chromosomal translocation

The 8;21 translocation is a common chromosomal abnormality in acute myeloid leukemia (AML). We recently identified a naturally occurring leukemogenic splice variant, AML1-ETO9a (acute myeloid leukemia-1 transcription factor and the eight-twenty-one corepressor-9a), of t(8;21). To understand the leukemic potential of AML1-ETO9a, we performed microarray analysis with the murine multipotential hematopoietic FDCP-mix A4 cell line. We identified changes in expression of various genes including CD44. CD44 is a type I transmembrane protein and functions as the major cellular adhesion molecule for hyaluronic acid, a component of the extracellular matrix. CD44 is expressed in most human cell types and is implicated in myeloid leukemia pathogenesis. We show that the presence of AML1-ETO9a significantly increased the expression of CD44 at both RNA and protein levels. Furthermore, the CD44 promoter is bound by AML1-ETO9a and AML1-ETO at the chromatin level. In addition, in the AML1-ETO9a leukemia mouse model CD44 is regulated in a cell context-dependent manner. Thus, our observations suggest that AML1-ETO and its splice variant AML1-ETO9a are able to regulate the expression of the CD44 gene, linking the 8;21 translocation to the regulation of a cell adhesion molecule that is involved in the growth and maintenance of the AML blast/stem cells.

Expression of AML/Runx and ETO/MTG family members during hematopoietic differentiation of embryonic stem cells

Runx1/AML1 plays important roles in hematopoiesis, including the commitment of cells to hematopoiesis during embryonic development, and in the maintenance of hematopoietic cell populations. It is also one of the most common genes involved in chromosomal translocations related to leukemia. One such translocation is t(8;21), which fuses the Runx1 gene to the MTG8/ETO gene and generates the Runx1-MTG8 (AML1-ETO) fusion gene. Both Runx1 and MTG8 have two additional family members that are much less studied in hematopoiesis. Here we report the expression of every member of the Runx and MTG families as well as the Runx heterodimerization partner CBFbeta during hematopoietic differentiation of murine embryonic stem cells. We observed substantially increased expression of Runx1, Runx2, and MTG16 during hematopoietic differentiation. Furthermore, the increase in Runx2 expression is delayed relative to Runx1 expression, suggesting their possible sequential contribution to hematopoiesis.

Acute myeloid leukemia with the 8q22;21q22 translocation: secondary mutational events and alternative t(8;21) transcripts

Nonrandom and somatically acquired chromosomal translocations can be identified in nearly 50% of human acute myeloid leukemias. One common chromosomal translocation in this disease is the 8q22;21q22 translocation. It involves the AML1 (RUNX1) gene on chromosome 21 and the ETO (MTG8, RUNX1T1) gene on chromosome 8 generating the AML1-ETO fusion proteins. In this review, we survey recent advances made involving secondary mutational events and alternative t(8;21) transcripts in relation to understanding AML1-ETO leukemogenesis.

The p21Waf1 pathway is involved in blocking leukemogenesis by the t(8;21) fusion protein AML1-ETO

The 8;21 translocation is a major contributor to acute myeloid leukemia (AML) of the M2 classification occurring in approximately 40% of these cases. Multiple mouse models using this fusion protein demonstrate that AML1-ETO requires secondary mutagenic events to promote leukemogenesis. Here, we show that the negative cell cycle regulator p21(WAF1) gene is up-regulated by AML1-ETO at the protein, RNA, and promoter levels. Retroviral transduction and hematopoietic cell transplantation experiments with p21(WAF1)-deficient cells show that AML1-ETO is able to promote leukemogenesis in the absence of p21(WAF1). Thus, loss of p21(WAF1) facilitates AML1-ETO-induced leukemogenesis, suggesting that mutagenic events in the p21(WAF1) pathway to bypass the growth inhibitory effect from AML1-ETO-induced p21(WAF1) expression can be a significant factor in AML1-ETO-associated acute myeloid leukemia.

A leukemia fusion protein attenuates the spindle checkpoint and promotes aneuploidy

The 8;21 chromosomal translocation occurs in 15% to 40% of patients with the FAB M2 subtype of acute myeloid leukemia (AML). This chromosomal abnormality fuses part of the AML1/RUNX1 gene to the ETO/MTG8 gene and generates the AML1-ETO protein. We previously identified a C-terminal truncated AML1-ETO protein (AEtr) in a mouse leukemia model. AEtr is almost identical to the AML1-ETO exon 9a isoform expressed in leukemia patients. Here, we describe a novel function of AEtr in the development of aneuploidy through spindle checkpoint attenuation. AEtr cells had a reduced mitotic index following nocodazole treatment, suggesting a failure in a subset of cells to arrest in mitosis with a functional spindle checkpoint. Additionally, primary leukemia cells and cell lines expressing AEtr were aneuploid. Moreover, AEtr cells had reduced levels of several spindle checkpoint proteins including BubR1 and securin following treatment with the spindle poison nocodazole. These results suggest that inactivation of the spindle checkpoint may contribute to the development of aneuploidy described in t(8;21) leukemia patients.

AML1/RUNX1 phosphorylation by cyclin-dependent kinases regulates the degradation of AML1/RUNX1 by the anaphase-promoting complex

AML1 (RUNX1) regulates hematopoiesis, angiogenesis, muscle function, and neurogenesis. Previous studies have shown that phosphorylation of AML1, particularly at serines 276 and 303, affects its transcriptional activation. Here, we report that phosphorylation of AML1 serines 276 and 303 can be blocked in vivo by inhibitors of the cyclin-dependent kinases (CDKs) Cdk1 and Cdk2. Furthermore, these residues can be phosphorylated in vitro by purified Cdk1/cyclin B and Cdk2/cyclin A. Mutant AML1 protein which cannot be phosphorylated at these sites (AML1-4A) is more stable than wild-type AML1. AML-4A is resistant to degradation mediated by Cdc20, one of the substrate-targeting subunits of the anaphase-promoting complex (APC). However, Cdh1, another targeting subunit used by the APC, can mediate the degradation of AML1-4A. A phospho-mimic protein, AML1-4D, can be targeted by Cdc20 or Cdh1. These observations suggest that both Cdc20 and Cdh1 can target AML1 for degradation by the APC but that AML1 phosphorylation may affect degradation mediated by Cdc20-APC to a greater degree.

A previously unidentified alternatively spliced isoform of t(8;21) transcript promotes leukemogenesis

The t(8;21)(q22;q22) translocation is one of the most common genetic abnormalities in acute myeloid leukemia (AML), identified in 15% of all cases of AML, including 40-50% of FAB M2 subtype and rare cases of M0, M1 and M4 subtypes. The most commonly known AML1-ETO fusion protein (full-length AML1-ETO) from this translocation has 752 amino acids and contains the N-terminal portion of RUNX1 (also known as AML1, CBFalpha2 or PEBP2alphaB), including its DNA binding domain, and almost the entire RUNX1T1 (also known as MTG8 or ETO) protein. Although alterations of gene expression and hematopoietic cell proliferation have been reported in the presence of AML1-ETO, its expression does not lead to the development of leukemia. Here, we report the identification of a previously unknown alternatively spliced isoform of the AML1-ETO transcript, AML1-ETO9a, that includes an extra exon, exon 9a, of the ETO gene. AML1-ETO9a encodes a C-terminally truncated AML1-ETO protein of 575 amino acids. Expression of AML1-ETO9a leads to rapid development of leukemia in a mouse retroviral transduction-transplantation model. More importantly, coexpression of AML1-ETO and AML1-ETO9a results in the substantially earlier onset of AML and blocks myeloid cell differentiation at a more immature stage. These results indicate that fusion proteins from alternatively spliced isoforms of a chromosomal translocation may work together to induce cancer development.

The hematopoietic transcription factor AML1 (RUNX1) is negatively regulated by the cell cycle protein cyclin D3

The family of cyclin D proteins plays a crucial role in the early events of the mammalian cell cycle. Recent studies have revealed the involvement of AML1 transactivation activity in promoting cell cycle progression through the induction of cyclin D proteins. This information in combination with our previous observation that a region in AML1 between amino acids 213 and 289 is important for its function led us to investigate prospective proteins associating with this region. We identified cyclin D3 by a yeast two-hybrid screen and detected AML1 interaction with the cyclin D family by both in vitro pull-down and in vivo coimmunoprecipitation assays. Furthermore, we demonstrate that cyclin D3 negatively regulates the transactivation activity of AML1 in a dose-dependent manner by competing with CBFbeta for AML1 association, leading to a decreased binding affinity of AML1 for its target DNA sequence. AML1 and its fusion protein AML1-ETO have been shown to shorten and prolong the mammalian cell cycle, respectively. In addition, AML1 promotes myeloid cell differentiation. Thus, our observations suggest that the direct association of cyclin D3 with AML1 functions as a putative feedback mechanism to regulate cell cycle progression and differentiation.

Phosphorylation of AML1/RUNX1 regulates its degradation and nuclear matrix association

The acute myeloid leukemia 1 (AML1) transcription factors are key regulators of hematopoietic differentiation. Cellular AML1c protein is found in the nucleus and can be separated into two fractions, one soluble in buffers containing salt and nonionic detergent and the other insoluble and tightly bound to the nuclear matrix. We find that the AML1c protein is modified by both phosphorylation and ubiquitination. Our studies show that the majority of the ubiquitinated AML1c is associated with the insoluble nuclear matrix. Treatment of cells with the proteasome inhibitor PS341 (Velcade, Bortezomib) increases the levels of ubiquitinated AML1c. Mutation of the four phosphorylation sites necessary for transcriptional regulation (serine 276, serine 293, serine 303, and threonine 300) mimics the effects of the proteasome inhibitor, increasing the levels of ubiquitinated, matrix-bound AML1c. We find that the soluble and insoluble forms of AML1c are degraded at a similar rate. However, mutation of these four serine/threonine residues statistically increases the half-life of the matrix-associated AML1c. Thus, phosphorylation of AML1c on specific serine/threonine residues controls both transcriptional activity and rate of degradation.

Deletion of an AML1-ETO C-terminal NcoR/SMRT-interacting region strongly induces leukemia development

Normal blood-cell differentiation is controlled by regulated gene expression and signal transduction. Transcription deregulation due to chromosomal translocation is a common theme in hematopoietic neoplasms. AML1-ETO, which is a fusion protein generated by the 8;21 translocation that is commonly associated with the development of acute myeloid leukemia, fuses the AML1 runx family DNA-binding transcription factor to the ETO corepressor that associates with histone deacetylase complexes. Analyses have demonstrated that AML1-ETO blocks AML1 function and requires additional mutagenic events to promote leukemia. Here, we report that the loss of the molecular events of AML1-ETO C-terminal NCoR/SMRT-interacting domain transforms AML1-ETO into a potent leukemogenic protein. Contrary to full-length AML1-ETO, the truncated form promotes in vitro growth and does not obstruct the cell-cycle machinery. These observations suggest a previously uncharacterized mechanism of tumorigenesis, in which secondary mutation(s) in molecular events disrupting the function of a domain of the oncogene promote the development of malignancy.

The 8;21 translocation in leukemogenesis

A common chromosomal translocation in acute myeloid leukemia (AML) involves the AML1 (acute myeloid leukemia 1, also called RUNX1, core binding factor protein (CBF alpha), and PEBP2 alpha B) gene on chromosome 21 and the ETO (eight-twenty one, also called MTG8) gene on chromosome 8. This translocation generates an AML1-ETO fusion protein. t(8;21) is associated with 12% of de novo AML cases and up to 40% in the AML subtype M2 of the French-American-British classification. Furthermore, it is also reported in a small portion of M0, M1, and M4 AML samples. Despite numerous studies on the function of AML1-ETO, the precise mechanism by which the fusion protein is involved in leukemia development is still not fully understood. In this review, we will discuss structural aspects of the fusion protein and the accumulated knowledge from in vitro analyses on AML1-ETO functions, and outline putative mechanisms of its leukemogenic potential.

Protein ISGylation modulates the JAK-STAT signaling pathway

ISG15 is one of the most strongly induced genes upon viral infection, type I interferon (IFN) stimulation, and lipopolysaccharide (LPS) stimulation. Here we report that mice lacking UBP43, a protease that removes ISG15 from ISGylated proteins, are hypersensitive to type I IFN. Most importantly, in UBP43-deficient cells, IFN-beta induces a prolonged Stat1 tyrosine phosphorylation, DNA binding, and IFN-mediated gene activation. Furthermore, restoration of ISG15 conjugation in protein ISGylation-defective K562 cells increases IFN-stimulated promoter activity. These findings identify UBP43 as a novel negative regulator of IFN signaling and suggest the involvement of protein ISGylation in the regulation of the JAK-STAT pathway.

Estrogen increases hyperemic microvascular blood flow velocity in postmenopausal women

BACKGROUND

Epidemiologic studies suggest that estrogen replacement therapy (ERT) is protective against vascular disease. ERT confers this benefit by lowering lipid levels and improving arterial function. However, its effect on the microvasculature in vivo is unknown. Thus the purposes of this study were to evaluate effect of estrogen status on the hyperemic response of the microvasculature in vivo in postmenopausal women and to compare the hyperemic response of the microvasculature in postmenopausal women taking ERT with that of premenopausal women.

METHODS

We measured forearm microvasculature flow velocity by using a laser Doppler in a cross section of 64 healthy premenopausal and postmenopausal women 23 to 72 years old. Microvasculature blood flow velocity was measured at baseline. throughout 2 minutes of ischemia, and immediately after the ischemic period was terminated (i.e., during the peak hyperemic response).

RESULTS

The peak of the hyperemic flow velocity (PHFV) in the postmenopausal women who were taking long-term ERT at usual doses was greater than that of postmenopausal women who were not currently taking ERT (p < .0001). Moreover, the PHFV of postmenopausal women taking ERT was similar to that of premenopausal women. Multivariate regression analysis showed estrogen status and baseline flow velocity to be independent predictors of PHFV.

CONCLUSIONS

Current, long-term ERT at usual replacement doses is associated with improved microvascular responses in postmenopausal women, which may explain some of its beneficial vascular effects.

Exclusion of the nuclear factor-kappa B3 (REL A) gene as candidate for the multiple endocrine neoplasia type 1 (MEN 1) gene

Multiple endocrine neoplasia type 1 (MEN 1) is inherited as an autosomal dominant disorder, characterized by neoplasia and hyperplasia in specific endocrine organs. The MEN 1 gene, which is most probably a tumor suppressor gene, has been localized to a region of approximately 900 kb on chromosome 11q13. The nuclear factor-kappa B (NF-kappa B) is a transcription factor with pleiotropic expression, which is involved in the regulation of expression of many cellular genes. The p50/p65 heterodimer is the most abundant form of NF-kappa B. The gene encoding the p65 subunit (NF-kappa B3/REL A) was recently localized in the 900-kb MEN 1 region and was considered a good candidate gene for MEN 1. The structure and nucleotide sequence of the NF-kappa B3 coding region in MEN 1 patients were compared with those of non-MEN 1 subjects, to determine the potential role of this gene in MEN 1 tumorigenesis. Southern blot analysis with constitutional DNA from probands of 14 independent MEN 1 families and DNA from four MEN 1 tumor specimens did not reveal any structural abnormality of the NF-kappa B3 gene. Direct sequencing of cDNAs from two affected subjects from 2 different MEN 1 families, as well as nucleotide sequence analysis of exon/intron boundaries in these patients, did not reveal MEN 1-specific point mutations or other small structural aberrations in the NF-kappa B3 gene. These results make it very unlikely that the NF-kappa B3 gene is the gene responsible for the development of MEN 1.

Polycentric total knee arthroplasty. A ten-year follow-up study

After review of the first 209 polycentric total knee arthroplasties (in 159 patients) performed at the Mayo Clinic between July 1970 and November 1971, we found that the calculated probability of the arthroplasty remaining successful ten years postoperatively was 66 per cent. Actual results showed 42 per cent of the arthroplasties to be successful in patients who were still alive at review; another 24 per cent were successful but were in patients who had died or were lost to follow-up before ten years postoperatively. In 34 per cent failure occurred, which we defined as reoperation for any reason, unacceptable pain, or loss of function. The most common causes of failure were instability or ligament laxity (13 per cent), loosening of a component (7 per cent), infection (3 per cent), and patellofemoral joint pain (4 per cent). Prior knee surgery significantly decreased the probability of success, as did axial malalignment of the prosthetic components at operation.

The snapping iliopsoas tendon

Herein we describe a previously seldom recognized variety of snapping hip, which is caused by snapping of the iliopsoas tendon over the iliopectineal eminence when the femur is moved from the flexed position at the hip and extended through 45 degrees of flexion. The finding is demonstrated with the patient supine and gently resisting gravity with the iliopsoas muscle, thus placing it under tension. At approximately 45 degrees of flexion, the iliopsoas tendon in two patients was confirmed radiographically to snap abruptly, coincident with an audible sound over the iliopectineal eminence of the pelvis. We believe that this occurs relatively frequently and is generally asymptomatic.

Unicompartmental knee arthroplasty using polycentric and geometric hemicomponents

Unicompartmental knee arthroplasty was performed in 207 knees of 179 patients using either a polycentric (188) or a geometric (nineteen) hemicomponent. After an average follow-up of 2.6 years, the results in 184 (89 per cent) of the knees were satisfactory. Pain and the need for ambulatory aids were reduced, and the distance the patients could walk was increased. Twenty-three (11 per cent) of the 207 procedures were rated as failures. The major cause of failure was loosening of the components (tibial in twelve and femoral in one); there also were unexplained pain in five knees, problems with the opposite unreplaced compartment in three, technical error in one, and pain in the patellofemoral joint in one. Nine of 155 intraoperative specimens for bacterial culture obtained during unicompartmental arthroplasty were positive, and two specimens that were positive on culture were obtained during revision of twenty failed unicompartmental arthroplasties. No gross or histological evidence of infection was demonstrated at operation. Based on this study, we concluded that this procedure can provide satisfactory relief of pain, adequate knee motion, and increased levels of independence and activity for patients with unicompartmental disease who are not suitable candidates for proximal tibial osteotomy or total knee replacement.

Polycentric total knee arthroplasty: a prognostic assessment

Polycentric total knee arthroplasty has been performed at the Mayo Clinic on more than 1,600 knees since July 1970. Two groups of 106 and 101 knee arthroplasties performed between July 1970 and July 1971 and June 1971 and January 1972, respectively, were compared at 5 and 7 years. The technique used exposed the joint to methacrylate particles, yet, despite this, wear did not prove to be a problem. Failures occurred because of infection, loosening of the tibial components, settling of the tibial components, subluxation or dislocation, ligamentous laxity, progression of patellofemoral arthritis, and persistence of pain. We did not encounter patellar problems in our patients with osteoarthritis. In the first group with 106 knees, 45 patients with 58 rheumatoid knees survived 7 years; 79% of knees had good results at 5 years and 72% had good results at 7 years. Twenty-one patients with 28 osteoarthritic knees survived 7 years; 75% of knees had good results at 5 years and 61% had good results at 7 years. In group 2 with 101 knees, 43 patients with 64 rheumatoid knees survived 7 years. The results were good in 83% at 5 years and in 64% at 7 years. Among the 20 patients with osteoarthritic knees who survived 7 years, 92% of knees had good results at 5 years and 62.5% had good results at 7 years. This figure is somewhat misleading because 7 patients were lost to follow up in group 2 after 5 years. There is still a need for a well-tolerated resurfacing procedure by means of a nonconstrained prosthesis.

Total joint arthroplasty. The knee

Total knee replacement has become an established form of treatment for gonarthrosis and usually results in excellent relief of pain and approximately 90 degrees of joint motion with satisfactory joint stability. The anatomic stability that cannot be restored at surgery must be provided for by additional prosthetic stability. Fixation of prosthetic devices, particularly in the tibia, is marginal and results in an increased incidence of loosening when the quality of bone is weak, as in osteoporosis, or when shear stress is increased because of malalignment or prosthetic constraint. Resurfacing techniques provide the greatest options if surgical revision is necessary. Surgical goals should be realistically assessed so as to maintain the best potential for future treatment options.

Arthrodesis of the knee following failed total knee arthroplasty

In forty-five patients, who had an arthrodesis because of failed total knee arthroplasty, the cause was infection in forty, instability in two, failure of the prosthesis in two, and loosening in one. The arthrodesis succeeded in twenty-nine (81%) of thirty-six patients who had had a minimally or partially constrained arthroplasty and in five (56%) of nine who had had a hinge-type prosthesis inserted. The reasons for failure were severe bone loss, persistent sepsis, and loss of bone apposition after manipulation. The technique of arthrodesis did not seem to influence the final result. External fixation most commonly had to be used because of the infections and the device was kept in place for an average of ten weeks, after which immobilization in a cast was used until the arthrodesis healed.