The Nature of Managerial Work: A Comparison of Public- and Private-Sector Managers

Little empirical information is available on the nature of managerial work. Such information is needed, not only for training and development programs but also for managerial selection, appraisal, and utilization. The purpose of this study was to compare high level managerial jobs in public and private sectors by examining job content, job characteristics, and required skills, knowledge, and abilities. Mintzberg's (1973, 1975) roles were used for the comparisons. Data were gathered from 210 public-sector and 220 private- sector managers and executives. Results indicate that managers in the public sector perform the same kind of activities as managers in the private sector in terms of complexity of job content and roles and in terms of job characteristics. The study has action implications for the selection, development, and appraisal systems of both public- and private-sector executives.

SGK3 mediates INPP4B-dependent PI3K signaling in breast cancer

Oncogenic mutations in PIK3CA, the gene encoding the catalytic subunit of phosphoinositide 3-kinase (PI3K), occur with high frequency in breast cancer. The protein kinase Akt is considered to be the primary effector of PIK3CA, although mechanisms by which PI3K mediates Akt-independent tumorigenic signals remain obscure. We show that serum and glucocorticoid-regulated kinase 3 (SGK3) is amplified in breast cancer and activated downstream of PIK3CA in a manner dependent on the phosphoinositide phosphatase INPP4B. Expression of INPP4B leads to enhanced SGK3 activation and suppression of Akt phosphorylation. Activation of SGK3 downstream of PIK3CA and INPP4B is required for 3D proliferation, invasive migration, and tumorigenesis in vivo. We further show that SGK3 targets the metastasis suppressor NDRG1 for degradation by Fbw7. We propose a model in which breast cancers harboring oncogenic PIK3CA activate SGK3 signaling while suppressing Akt, indicative of oncogenic functions for both INPP4B and SGK3 in these tumors.

Acetylation-dependent regulation of essential iPS-inducing factors: a regulatory crossroad for pluripotency and tumorigenesis

Induced pluripotent stem (iPS) cells can be generated from somatic cells by coexpression of four transcription factors: Sox2, Oct4, Klf4, and c-Myc. However, the low efficiency in generating iPS cells and the tendency of tumorigenesis hinder the therapeutic applications for iPS cells in treatment of human diseases. To this end, it remains largely unknown how the iPS process is subjected to regulation by upstream signaling pathway(s). Here, we report that Akt regulates the iPS process by modulating posttranslational modifications of these iPS factors in both direct and indirect manners. Specifically, Akt directly phosphorylates Oct4 to modulate the Oct4/Sox2 heterodimer formation. Furthermore, Akt either facilitates the p300-mediated acetylation of Oct4, Sox2, and Klf4, or stabilizes Klf4 by inactivating GSK3, thus indirectly modulating stemness. As tumorigenesis shares possible common features and mechanisms with iPS, our study suggests that Akt inhibition might serve as a cancer therapeutic approach to target cancer stem cells.

SIRT1 phosphorylation by AMP-activated protein kinase regulates p53 acetylation

The deacetylase SIRT1 regulates multiple biological processes including cellular metabolism and aging. Importantly, SIRT1 can also inactivate the p53 tumor suppressor via deacetylation, suggesting a role in oncogenesis. Recently, SIRT1 was shown to be released from its endogenous inhibitor DBC1 by a process requiring AMPK and the phosphorylation of SIRT1 by yet undefined kinase(s). Here we provide further evidence that AMPK directly phosphorylates SIRT1 on T344, releasing it from DBC1. Furthermore, a phospho-mimetic SIRT1 (T334E) showed decreased binding to DBC1, supporting the importance of this phosphorylation in AMPK-mediated regulation of SIRT1 activity. In addition, inhibition of AMPK by Compound C led to increased p53 acetylation, suggesting a role for the AMPK/SIRT1 pathway in regulating p53 signaling. Together, our results support a hypothesis that AMPK negatively regulates p53 acetylation via phosphorylation of SIRT1 on T344. Furthermore, our findings also define the AMPK/SIRT1 axis as a possible targetable pathway to regulate p53 function.

SCF-mediated Cdh1 degradation defines a negative feedback system that coordinates cell-cycle progression

Proper cell-cycle transitions are driven by waves of ubiquitin-dependent degradation of key regulators by the anaphase-promoting complex (APC) and Skp1-Cullin1-F-box (SCF) E3 ubiquitin ligase complexes. But precisely how APC and SCF activities are coordinated to regulate cell-cycle progression remains largely unclear. We previously showed that APC/Cdh1 earmarks the SCF component Skp2 for degradation. Here, we continue to report that SCF(β-TRCP) reciprocally controls APC/Cdh1 activity by governing Cdh1 ubiquitination and subsequent degradation. Furthermore, we define both cyclin A and Plk1, two well-known Cdh1 substrates, as upstream modifying enzymes that promote Cdh1 phosphorylation to trigger Cdh1 ubiquitination and subsequent degradation by SCF(β-TRCP). Thus, our work reveals a negative repression mechanism for SCF to control APC, thereby illustrating an elegant dual repression system between these two E3 ligase complexes to create the ordered cascade of APC and SCF activities governing timely cell-cycle transitions.

SCF(Fbw7) modulates the NFkB signaling pathway by targeting NFkB2 for ubiquitination and destruction

The NFkB/Rel family of proteins play critical roles in a variety of cellular processes. Thus, their physiological activation is tightly controlled. Recently, the NFkB2/p100 precursor has been characterized as the fourth IkB type of suppressor for NFkB. However, the molecular mechanism(s) underlying regulated destruction of NFkB2 remains largely unknown. Here, we report that, unlike other IkBs, ubiquitination and destruction of NFkB2 are governed by SCF(Fbw7) in a GSK3-dependent manner. In Fbw(7-/-) cells, elevated expression of NFkB2/p100 leads to a subsequent reduction in NFkB signaling pathways and elevated sensitivity to TNFa-induced cell death. Reintroducing wild-type Fbw7, but not disease-derived mutant forms of Fbw7, rescues NFkB activity. Furthermore, T cell-specific depletion of Fbw7 also leads to reduced NFkB activity and perturbed T cell differentiation. Therefore, our work identifies Fbw7 as a physiological E3 ligase controlling NFkB20s stability. It further implicates that Fbw7 might exert its tumor-suppressor function by regulating NFkB activity.

Acetylation-dependent regulation of Skp2 function

Aberrant Skp2 signaling has been implicated as a driving event in tumorigenesis. Although the underlying molecular mechanisms remain elusive, cytoplasmic Skp2 correlates with more aggressive forms of breast and prostate cancers. Here, we report that Skp2 is acetylated by p300 at K68 and K71, which is a process that can be antagonized by the SIRT3 deacetylase. Inactivation of SIRT3 leads to elevated Skp2 acetylation, which leads to increased Skp2 stability through impairment of the Cdh1-mediated proteolysis pathway. As a result, Skp2 oncogenic function is increased, whereby cells expressing an acetylation-mimetic mutant display enhanced cellular proliferation and tumorigenesis in vivo. Moreover, acetylation of Skp2 in the nuclear localization signal (NLS) promotes its cytoplasmic retention, and cytoplasmic Skp2 enhances cellular migration through ubiquitination and destruction of E-cadherin. Thus, our study identifies an acetylation-dependent regulatory mechanism governing Skp2 oncogenic function and provides insight into how cytoplasmic Skp2 controls cellular migration.

The Fbw7 and betaTRCP E3 ubiquitin ligases and their roles in tumorigenesis

The Ubiquitin Proteasome System (UPS) is a major regulator of protein abundance in the cell. The UPS influences the functions of multiple biological processes by targeting key regulators for destruction. E3 ubiquitin ligases are a vital component of the UPS machinery, working with E1 and E2 enzymes to bind substrates and facilitate the transfer of ubiquitin molecules onto the target protein. This poly-ubiquitination, in turn, directs the modified proteins for proteolysis by the 26S proteasome. As the UPS regulates the degradation of multiple oncogenes and tumor suppressors, the dysregulation of this pathway is known to promote various diseases including cancer. While E1 and E2 enzymes have only been minimally linked to cancer development, burgeoning amounts of evidence have implicated loss or gain of E3 function as a key factor in cancer initiation and progression. This review will examine the literature on two SCF-type E3 ligases, SCFFbw7 and SCFbeta-TRCP. In particular, we will highlight novel substrates recently identified for these two E3 ligases, and further discuss how UPS regulation of these targets may promote carcinogenesis.

Negative regulation of the stability and tumor suppressor function of Fbw7 by the Pin1 prolyl isomerase

Fbw7 is the substrate recognition component of the Skp1-Cullin-F-box (SCF)-type E3 ligase complex and a well-characterized tumor suppressor that targets numerous oncoproteins for destruction. Genomic deletion or mutation of FBW7 has been frequently found in various types of human cancers; however, little is known about the upstream signaling pathway(s) governing Fbw7 stability and cellular functions. Here we report that Fbw7 protein destruction and tumor suppressor function are negatively regulated by the prolyl isomerase Pin1. Pin1 interacts with Fbw7 in a phoshorylation-dependent manner and promotes Fbw7 self-ubiquitination and protein degradation by disrupting Fbw7 dimerization. Consequently, overexpressing Pin1 reduces Fbw7 abundance and suppresses Fbw7's ability to inhibit proliferation and transformation. By contrast, depletion of Pin1 in cancer cells leads to elevated Fbw7 expression, which subsequently reduces Mcl-1 abundance, sensitizing cancer cells to Taxol. Thus, Pin1-mediated inhibition of Fbw7 contributes to oncogenesis, and Pin1 may be a promising drug target for anticancer therapy.

Nodular fasciitis: a novel model of transient neoplasia induced by MYH9-USP6 gene fusion

Nodular fasciitis (NF) is a relatively common mass-forming and self-limited subcutaneous pseudosarcomatous myofibroblastic proliferation of unknown pathogenesis. Due to its rapid growth and high mitotic activity, NF is often misdiagnosed as a sarcoma. While studying the USP6 biology in aneurysmal bone cyst and other mesenchymal tumors, we identified high expression levels of USP6 mRNA in two examples of NF. This finding led us to further examine the mechanisms underlying USP6 overexpression in these lesions. Upon subsequent investigation, genomic rearrangements of the USP6 locus were found in 92% (44 of 48) of NF. Rapid amplification of 5'-cDNA ends identified MYH9 as the translocation partner. RT-PCR and direct sequencing revealed the fusion of the MYH9 promoter region to the entire coding region of USP6. Control tumors and tissues were negative for this fusion. Xenografts of cells overexpressing USP6 in nude mice exhibited clinical and histological features similar to human NF. The identification of a sensitive and specific abnormality in NF holds the potential to be used diagnostically. Considering the self-limited nature of the lesion, NF may represent a model of 'transient neoplasia', as it is, to our knowledge, the first example of a self-limited human disease characterized by a recurrent somatic gene fusion event.

The two faces of FBW7 in cancer drug resistance

Chemotherapy is an important therapeutic approach for cancer treatment. However, drug resistance is an obstacle that often impairs the successful use of chemotherapies. Therefore, overcoming drug resistance would lead to better therapeutic outcomes for cancer patients. Recently, studies by our own and other groups have demonstrated that there is an intimate correlation between the loss of the F-box and WD repeat domain-containing 7 (FBW7) tumor suppressor and the incurring drug resistance. While loss of FBW7 sensitizes cancer cells to certain drugs, FBW7-/- cells are more resistant to other types of chemotherapies. FBW7 exerts its tumor suppressor function by promoting the degradation of various oncoproteins that regulate many cellular processes, including cell cycle progression, cellular metabolism, differentiation, and apoptosis. Since loss of the FBW7 tumor suppressor is linked to drug resistance, FBW7 may represent a novel therapeutic target to increase drug sensitivity of cancer cells to conventional chemotherapeutics. This paper thus focuses on the new functional aspects of FBW7 in drug resistance.

Mcl-1 ubiquitination and destruction

Loss of the Fbw7 tumor suppressor is common in diverse human cancer types, including T-Cell Acute Lymphoblastic Leukemia (T-ALL), although the mechanistic basis of its anti-oncogenic activity remains largely unclear. We recently reported that SCFFbw7 regulates cellular apoptosis by controlling the ubiquitination and destruction of the pro-survival protein, Mcl-1, in a GSK3 phosphorylation-dependent manner. We found that human T-ALL cell lines displayed a close relationship between Fbw7 loss and Mcl-1 overexpression. More interestingly, T-ALL cell lines that are deficient in Fbw7 are particularly sensitive to sorafenib, a multi-kinase inhibitor that has been demonstrated to reduce Mcl-1 expression through an unknown mechanism. On the other hand, Fbw7-deficient T-ALL cell lines are much more resistant to the Bcl-2 antagonist, ABT-737. Furthermore, reconstitution of Fbw7 or depletion of Mcl-1 in Fbw7-deficient cells restores ABT-737 sensitivity, suggesting that elevated Mcl-1 expression is important for Fbw7-deficient cells to evade apoptosis. Therefore, our work provides a novel molecular mechanism for the tumor suppression function of Fbw7. Furthermore, it provides the rationale for targeted usage of Mcl-1 antagonists to treat Fbw7-deficient T-ALL patients.

SCF(FBW7) regulates cellular apoptosis by targeting MCL1 for ubiquitylation and destruction

The effective use of targeted therapy is highly dependent upon the identification of responder patient populations. Loss of the Fbw7 tumor suppressor is frequently found in various types of human cancers including breast cancer, colon cancer 1 and T-cell acute lymphoblastic leukemia (T-ALL)2. In line with these genomic data, engineered deletion of Fbw7 in mouse T cells results in T-ALL3–5, validating Fbw7 as a T-ALL tumor suppressor. The precise molecular mechanisms by which Fbw7 exerts anti-tumor activity remain areas of intensive investigation and are thought to relate in part to Fbw7-mediated destruction of key cancer relevant proteins including c-Jun6, c-Myc 7, Cyclin E 8 and Notch-19, all of which possess oncogenic activity and are overexpressed in various human cancers including leukemia. Besides accelerating cell growth 10, overexpression of either c-Jun, c-Myc or Notch-1 can also provoke programmed cell death 11. Thus, considerable uncertainty surrounds how Fbw7-deficient cells evade cell death in the setting of upregulated c-Jun, c-Myc and/or Notch-1. Here we report that SCF^Fbw7 governs cellular apoptosis by targeting the pro-survival Bcl-2 family member, Mcl-1, for ubiquitination and destruction in a GSK3 phosphorylation-dependent manner. Human T-ALL cell lines showed a close relationship between Fbw7 loss and Mcl-1 overexpression. Correspondingly, T-ALL cell lines with defective Fbw7 are particularly sensitive to the multi-kinase inhibitor, sorafenib, but resistant to the Bcl-2 antagonist, ABT-737. On the genetic level, Fbw7 reconstitution or Mcl-1 depletion restores ABT-737 sensitivity, establishing Mcl-1 as a therapeutically relevant bypass survival mechanism for Fbw7-deficient cells to evade apoptosis. Therefore, our work provides novel molecular insight into Fbw7-direct tumor suppression with direct implications for the targeted treatment of Fbw7-deficient T-ALL patients.

TRE17/ubiquitin-specific protease 6 (USP6) oncogene translocated in aneurysmal bone cyst blocks osteoblastic maturation via an autocrine mechanism involving bone morphogenetic protein dysregulation

Aneurysmal bone cyst (ABC) is a pediatric osseous tumor characterized by extensive destruction of the surrounding bone. The molecular mechanisms underlying its pathogenesis are completely unknown. Recent work showed that translocation of the TRE17/USP6 locus occurs in over 60% of ABC cases resulting in TRE17 overexpression. Immature osteoblasts are presumed to be the cell type harboring translocation of TRE17 in at least a subset of ABCs. However, the effects of TRE17 overexpression on transformation and osteoblast function are unknown. TRE17 encodes a ubiquitin-specific protease (USP) and a TBC (TRE2-Bub2-Cdc16) domain that promotes activation of the Arf6 GTPase. Here we report that TRE17 potently inhibits the maturation of MC3T3 pre-osteoblasts in a USP-dependent and Arf6-independent manner. Notably, we find that TRE17 function is mediated through an autocrine mechanism. Transcriptome analysis of TRE17-expressing cells reveals dysregulation of several pathways with established roles in osteoblast maturation. In particular, signaling through the bone morphogenetic protein (BMP) pathway, a key regulator of osteogenesis, is profoundly altered. TRE17 simultaneously inhibits the expression of BMP-4 while augmenting the BMP antagonist, Gremlin-1. Osteoblastic maturation is restored in TRE17-expressing cells by the addition of exogenous BMP-4, thus establishing a functional role for BMP-4 during TRE17-induced transformation. Because bone homeostasis involves a precise balance between the activities of osteoblasts and osteoclasts, our studies raise the possibility that attenuated osteoblast maturation caused by TRE17 overexpression may contribute to the bone loss/destruction observed in ABC.

TRE17/USP6 oncogene translocated in aneurysmal bone cyst induces matrix metalloproteinase production via activation of NF-kappaB

Aneurysmal bone cyst (ABC) is an aggressive, pediatric bone tumor characterized by extensive destruction of the surrounding bone. Though first described over 60 years ago, its molecular etiology remains poorly understood. Recent work revealed that ABCs harbor translocation of TRE17/USP6, leading to its transcriptional upregulation. TRE17 encodes a ubiquitin-specific protease (USP), and a TBC domain that mediates binding to the Arf6 GTPase. However, the mechanisms by which TRE17 overexpression contributes to tumor pathogenesis, and the role of its USP and TBC domains are unknown. ABCs are characterized by osteolysis, inflammatory recruitment, and extensive vascularization, processes in which matrix proteases play a prominent role. This led us to explore whether TRE17 regulates the production of matrix metalloproteinases (MMPs). In the current study, we demonstrate that TRE17 is sufficient to induce expression of MMP-9 and MMP-10, in a manner requiring its USP activity, but not its ability to bind Arf6. TRE17 induces transcription of MMP-9 through activation of NFκB, mediated in part by the GTPase RhoA and its effector kinase, ROCK. Furthermore, xenograft studies demonstrate that TRE17 induces formation of tumors that reproduce multiple features of ABC, including a high degree of vascularization, with an essential role for the USP domain. In sum, these studies reveal that TRE17 is sufficient to initiate tumorigenesis, identify MMPs as novel TRE17 effectors that likely contribute to ABC pathogenesis, and define the underlying signaling mechanism of their induction.

A reconfigured pattern of MLL occupancy within mitotic chromatin promotes rapid transcriptional reactivation following mitotic exit

Mixed lineage leukemia (MLL) and its metazoan Trithorax orthologs have been linked with the epigenetic maintenance of transcriptional activity. To identify mechanisms by which MLL perpetuates active transcription in dividing cells, we investigated its role during M phase of the cell cycle. Unlike other chromatin-modifying enzymes examined, we found that MLL associates with gene promoters packaged within condensed mitotic chromosomes. Genome-wide location analysis identified a globally rearranged pattern of MLL occupancy during mitosis in a manner favoring genes that were highly transcribed during interphase. Knockdown experiments revealed that MLL retention at gene promoters during mitosis accelerates transcription reactivation following mitotic exit. MLL tethers Menin, RbBP5, and ASH2L to its occupied sites during mitosis, but is dispensable for preserving histone H3K4 methylation. These findings implicate mitotic bookmarking as a component of Trithorax-based gene regulation, which may facilitate inheritance of active gene expression states during cell division.

The adaptor complex AP-2 regulates post-endocytic trafficking through the non-clathrin Arf6-dependent endocytic pathway

The ADP-ribosylation factor 6 (Arf6) GTPase functions as a key regulator of endocytic trafficking, participating in clathrin-independent endocytosis in most cell types. Unexpectedly, we found that siRNA-mediated depletion of clathrin or of adaptor protein 2 (AP-2)-complex subunits alters trafficking of Arf6 pathway cargo proteins, such as major histocompatibility complex class I (MHCI) and beta1 integrin. Internalization of these cargoes from the plasma membrane was not affected in cells depleted of clathrin, but was modestly delayed in cells lacking AP-2. Furthermore, depletion of clathrin or AP-2 altered the intracellular distribution of MHCI and beta1 integrin, inducing clustering in a perinuclear region. Despite this altered localization in both depleted populations, enhanced lysosomal targeting of MHCI was observed uniquely in cells that lack AP-2. Total levels of MHCI were modestly but consistently reduced in AP-2-depleted cells, and restored by the lysosomal inhibitor bafilomycin A. Furthermore, the half-life of surface-derived MHCI was reduced in AP-2-depleted cells. Consistent with enhanced degradative sorting, colocalization of Arf6 cargo with the late endosome and lysosome markers CD63 and Lamp1 was increased in cells depleted of AP-2 but not clathrin. These studies indicate a role for AP-2 in maintaining normal post-endocytic trafficking through the Arf6-regulated, non-clathrin pathway, and reveal pervasive effects of clathrin and AP-2 depletion on the endosomal and lysosomal system.

Calcium/calmodulin regulates ubiquitination of the ubiquitin-specific protease TRE17/USP6

The TRE17 (USP6/TRE-2) oncogene induces tumorigenesis in both humans and mice. However, little is known regarding its regulation or mechanism of transformation. TRE17 encodes a TBC (Tre-2/Bub2/Cdc16)/Rab GTPase-activating protein homology domain at its N terminus and a ubiquitin-specific protease at its C terminus. In the current study, we identified the ubiquitous calcium (Ca2+)-binding protein calmodulin (CaM) as a novel binding partner for TRE17. CaM bound directly to TRE17 in a Ca2+-dependent manner both in vitro and in vivo. The CaM-binding site was mapped to two hydrophobic motifs near the C terminus of the TBC domain. Point mutations within these motifs significantly reduced the interaction of TRE17 with CaM. We further found that TRE17 is monoubiquitinated and promotes its own deubiquitination in vivo. CaM binding-deficient mutants of TRE17 exhibited significantly reduced monoubiquitination, suggesting that binding of Ca2+/CaM to TRE17 promotes this modification. Consistent with this notion, treatment of cells with the CaM inhibitor W7 reduced levels of TRE17 monoubiquitination. Interestingly, the calcium ionophore A23187 induced accumulation of a polyubiquitinated TRE17 species. The effect of A23187 was attenuated in CaM binding-deficient mutants of TRE17. Taken together, these studies indicate a role for Ca2+/CaM in regulating ubiquitination through direct interaction with TRE17.

Psychophysiological arousal in older adults: a critical review

In spite of the relatively high prevalence rates of anxiety disorders (AD) and related symptoms, very little is known about the experience, presentation, and assessment of anxiety in later life. Because the physiology of the autonomic nervous system changes with age, an enhanced understanding of how these developmental changes affect the somatic-physiological response patterns to anxiety-evoking stimuli among older adults may help explain whether we can generalize current assessment and treatment practices and procedures for AD from younger to older adults. In this paper, we describe and critically evaluate studies that have employed psychophysiological recording of autonomic arousal to anxiety-arousing or stressful stimuli among samples of younger and older adults. The conclusions one can draw from the review are quite limited by both the paucity of relevant literature and the methodological limitations of the published studies.

Electrostatic attraction of coupled Wigner crystals: finite temperature effects

In this paper we present a unified physical picture for the electrostatic attraction between two coupled planar Wigner crystals at finite temperature. This model may facilitate our conceptual understanding of counterion-mediated attractions between (highly) similarly charged planes. By adopting an elastic theory, we show that the total attractive force between them can be (approximately) decomposed into a short-ranged and a long-ranged component. They are evaluated below the melting temperature of the Wigner crystals. In particular, we analyze the temperature dependence of the short-ranged attraction, arising from ground-state configuration, and we argue that thermal fluctuations may drastically reduce its strength. Also, the long-range force agrees exactly with that based on the charge-fluctuation approach. Furthermore, we take quantum contributions to the long-ranged (fluctuation-induced) attraction into account and show how the fractional power law, which scales as d(-7/2) for large interplanar distance d at zero temperature, crosses over to the classical regime d(-3) via an intermediate regime of d(-2).

A possible role of p73 on the modulation of p53 level through MDM2

MDM2, one of the transcriptional targets of p53, can target p53 for degradation in a negative feedback loop. The p53-related protein p73, however, can bind to MDM2 but is not consequently down-regulated. Here we demonstrate that p73 could transactivate the MDM2 promoter in p53-null cell lines. In p53-null cell lines, the level of MDM2 was increased by p73 due to increases in transcription and protein stability of MDM2. In transient transfection assays, inhibition of the transcriptional activity of p73 required a higher amount of MDM2 than that of p53. This is probably due to the fact that MDM2 can target p53, but not p73, for degradation. We demonstrated further that the level of p53 could be altered by a cooperation between MDM2 and p73, but not by transcriptional inactive mutants of p73. Expression of p73 resulted in a reduction of the ectopically expressed p53 in transient transfections or of the endogenous p53 induced by Adriamycin- or UV-mediated damage. These reductions of p53 were likely to be due to an increase in MDM2-mediated proteolysis. These results suggest the possibility that different levels of p73 in the cell may act as a mechanism to modulate p53 responses after DNA damage and other stresses and that an increase rather than a decrease in p73 may play a role in tumorigenesis.

Novel electrostatic attraction from plasmon fluctuations

In this Letter, we show that, at low temperatures, zero-point fluctuations of the plasmon modes of two mutually coupled 2D planar Wigner crystals give rise to a novel long-range attractive force. For the case where the distance d between two planar surfaces is large, this attractive force has an unusual power-law decay, which scales as d(-7/2), unlike other fluctuation-induced forces. Specifically, we note that its range is longer than the "standard" zero-temperature van der Waals interaction. This result may, in principle, be observed in bilayer electronic systems and provides insight into the nature of correlation effects for highly charged surfaces.

Activation of NF-kappaB/Rel occurs early during neoplastic transformation of mammary cells

NF-kappaB/Rel is a family of transcription factors which are expressed in all cells; however, in most non-B cells, they are sequestered in the cytoplasm in inactive complexes with specific inhibitory proteins, termed IkappaBs. We have recently shown that NF-kappaB/Rel factors are aberrantly activated in human breast cancer and rodent mammary tumors, and function to promote tumor cell survival and proliferation. Here, we have examined the time-course of induction of NF-kappaB/Rel factors upon carcinogen treatment of female Sprague-Dawley (S-D) rats in vivo and in human mammary epithelial cells (HMECs) in culture. We observed that NF-kappaB/Rel activation is an early event, occurring prior to malignant transformation. In S-D rats, increased NF-kappaB/Rel binding was detected in nuclear extracts of mammary glands from 40% of animals 3 weeks post-treatment with 15 mg/kg 7,12-dimethylbenz[a]anthracene (DMBA); this is prior to formation of tumors which normally begin to be detected after 7-9 weeks. In non-tumorigenic MCF-10F cells, in vitro malignant transformation upon treatment with either DMBA or benzo[a]pyrene (B[a]P) resulted in a 4- to 12-fold increase in activity of classical NF-kappaB (p65/p50). NF-kappaB induction was corrrelated with a decrease in the stability of the NF-kappaB-specific inhibitory protein IkappaB-alpha. Ectopic expression of the transactivating p65 subunit of NF-kappaB in MCF-10F cells induced the c-myc oncogene promoter, which is driven by two NF-kappaB elements, and endogenous c-Myc levels. Furthermore, reduction mammoplasty-derived HMECs, immortalized following B[a]P exposure, showed dysregulated induction of classical NF-kappaB prior to malignant transformation. Together these findings suggest that activation of NF-kappaB plays an early, critical role in the carcinogen-driven transformation of mammary glands.

MDM2 and MDMX bind and stabilize the p53-related protein p73

The p53 gene encodes one of the most important tumor suppressors in human cells and undergoes frequent mutational inactivation in cancers. MDM2, a transcriptional target of p53, binds p53 and can both inhibit p53-mediated transcription [1] [2] and target p53 for proteasome-mediated proteolysis [3] [4]. A close relative of p53, p73, has recently been identified [5] [6]. Here, we report that, like p53, p73alpha and the alternative transcription product p73beta also bind MDM2. Interaction between MDM2 and p53 represents a key step in the regulation of p53, as MDM2 promotes the degradation of p53. In striking contrast to p53, the half-life of p73 was found to be increased by binding to MDM2. Like MDM2, the MDM2-related protein MDMX also bound p73 and stabilized the level of p73. Moreover, the growth suppression functions of p73 and the induction of endogenous p21, a major mediator of the p53-dependent growth arrest pathway, were enhanced in the presence of MDM2. These differences between the regulation of p53 and p73 by MDM2/MDMX may highlight a physiological difference in their action.

Regulation of cyclin A-Cdk2 by SCF component Skp1 and F-box protein Skp2

Cyclin A-Cdk2 complexes bind to Skp1 and Skp2 during S phase, but the function of Skp1 and Skp2 is unclear. Skp1, together with F-box proteins like Skp2, are part of ubiquitin-ligase E3 complexes that target many cell cycle regulators for ubiquitination-mediated proteolysis. In this study, we investigated the potential regulation of cyclin A-Cdk2 activity by Skp1 and Skp2. We found that Skp2 can inhibit the kinase activity of cyclin A-Cdk2 in vitro, both by direct inhibition of cyclin A-Cdk2 and by inhibition of the activation of Cdk2 by cyclin-dependent kinase (CDK)-activating kinase phosphorylation. Only the kinase activity of Cdk2, not of that of Cdc2 or Cdk5, is reduced by Skp2. Skp2 is phosphorylated by cyclin A-Cdk2 on residue Ser76, but nonphosphorylatable mutants of Skp2 can still inhibit the kinase activity of cyclin A-Cdk2 toward histone H1. The F box of Skp2 is required for binding to Skp1, and both the N-terminal and C-terminal regions of Skp2 are involved in binding to cyclin A-Cdk2. Furthermore, Skp2 and the CDK inhibitor p21(Cip1/WAF1) bind to cyclin A-Cdk2 in a mutually exclusive manner. Overexpression of Skp2, but not Skp1, in mammalian cells causes a G1/S cell cycle arrest.

Characterization of the cullin and F-box protein partner Skp1

Skp1 interacts with cullins, F-box containing proteins, and forms a complex with cyclin A-Cdk2 in mammalian cells. Skp1 is also involved in diverse biological processes like degradation of key cell cycle regulators, glucose sensing, and kinetochore function. However, little is known about the structure and exact function of Skp1. Here we characterized the interaction between Skp1 and the F-box protein Skp2. We show that Skp1 can bind to Skp2 in vitro using recombinant proteins, and in vivo using the yeast two-hybrid system. Deletion analysis of Skp1 indicated that most of the Skp1 protein is required for binding to Skp2. In mammalian cell extracts, a large portion of Skp1 appears to associate with proteins other than Skp2. Biochemical analysis indicated that Skp1 is likely to be a flexible, non-spherical protein, and is capable of forming dimers.

Skewed X-chromosome inactivation is common in fetuses or newborns associated with confined placental mosaicism

The inactivation of one X chromosome in females is normally random with regard to which X is inactivated. However, exclusive or almost-exclusive inactivation of one X may be observed in association with some X-autosomal rearrangements, mutations of the XIST gene, certain X-linked diseases, and MZ twinning. In the present study, a methylation difference near a polymorphism in the X-linked androgen-receptor gene was used to investigate the possibility that nonrandom X inactivation is increases in fetuses and newborns that are associated with confined placental mosaicism (CPM) involving an autosomal trisomy. Extreme skewing was observed in 7 (58%) of 12 cases with a meiotic origin of the trisomy, but in none of 10 cases examined with a somatic origin of the trisomy, and in only 1 (4%) of 27 control adult females. In addition, an extremely skewed X-inactivation pattern was observed in 3 of 10 informative cases of female uniparental disomy (UPD) of chromosome 15. This may reflect the fact that a proportion of UPD cases arise by "rescue" of a chromosomally abnormal conceptus and are therefore associated with CPM. A skewed pattern of X inactivation in CPM cases is hypothesized to result from a reduction in the size of the early-embryonic cell pool, because of either poor early growth or subsequent selection against the trisomic cells. Since approximately 2% of pregnancies detected by chorionic villus sampling are associated with CPM, this is likely a significant contributor to both skewed X inactivation observed in the newborn population and the expression of recessive X-linked diseases in females.