Metallothioneins are small, cysteine-rich proteins that avidly bind heavy metals such as zinc, copper, and cadmium to reduce their concentration to a physiological or nontoxic level. Metallothionein gene transcription is induced by several stimuli, notably heavy metal load and oxidative stress. Transcriptional induction of metallothionein genes is mediated by the metal-responsive transcription factor 1 (MTF-1), an essential zinc finger protein that binds to specific DNA motifs termed metal-response elements. In cell-free DNA binding reactions with nuclear extracts, MTF-1 requires elevated zinc concentrations for efficient DNA binding but paradoxically is inactivated by other in vivo inducers such as cadmium, copper, and hydrogen peroxide. Here we have developed a cell-free, MTF-1-dependent transcription system which accurately reproduces the activation of metallothionein gene promoters not only by zinc but also by these other inducers. We found that while transcriptional induction by zinc can be achieved by elevated zinc concentration alone, induction by cadmium, copper, or H 2 O 2 additionally requires the presence of zinc-saturated metallothionein. This is explained by the preferential binding of cadmium or copper to metallothionein or its oxidation by H 2 O 2 ; the concomitant release of zinc in turn leads to the activation of transcription factor MTF-1. Conversely, thionein, the metal-free form of metallothionein, inhibits activation of MTF-1. The release of zinc from cellular components, including metallothioneins, and the sequestration of zinc by newly produced apometallothionein might be a basic mechanism to regulate MTF-1 activity upon cellular stress.All living organisms are able to cope with a variety of stress situations by immediately adapting their gene expression program to the stress stimulus. For example, metallothioneins, small cysteine-rich proteins, are strongly upregulated upon heavy metal load (2,27,29,49,63,70,71). They have the ability to bind and hence neutralize toxic (such as Cd and Hg) and excess nontoxic (such as Zn and Cu) heavy metal ions and also act as radical scavengers. Metal response element binding transcription factor 1, also called metal-responsive transcription factor 1 (MTF-1), plays an important role in the cellular response to heavy metal stress (2,21,38,55,75) and is essential for embryonic liver development in the mouse (24). MTF-1 contains six zinc fingers of the C 2 H 2 type. C-terminal to the zinc fingers are three distinct activation domains, an acidic, a proline-rich, and a serine/threonine-rich domain. Via the zinc fingers, it binds to DNA sequence motifs with the consensus binding site TGCRCNC, known as metal response elements (MREs). MREs are present in the promoters of metallothionein genes (41,61,64) and other target genes, including zinc transporter ZnT1 and ␥-glutamylcysteine synthetase heavy chain (24,34,37). MTF-1 is also involved in the responses to oxidative stress (16, 24), hypoxia (23, 46), and amino acid starvation (1). In quiescent cells, MTF-1 pref...

F-box and WD repeat domain-containing 7 (FBW7) is the substrate recognition component of the Skp1-Cul1-F-box (SCF) ubiquitin ligase complex and functions as a major tumor suppressor by targeting various oncoproteins for degradation. Genomic deletion or mutation of FBW7 has frequently been identified in many human cancers but not in pancreatic ductal adenocarcinoma. Thus it is important to know how the tumor suppressive function of FBW7 is impaired in pancreatic cancer. In this study, we first observed that low FBW7 expression correlated significantly with ERK activation in pancreatic cancer clinical samples, primarily due to KRAS mutations in pancreatic cancer. We further showed that ERK directly interacted with FBW7 and phosphorylated FBW7 at Thr205, which sequentially promoted FBW7 ubiquitination and proteasomal degradation. Furthermore, the phospho-deficient T205A FBW7 mutant is resistant to ERK activation and could significantly suppress pancreatic cancer cell proliferation and tumorigenesis. These results collectively demonstrate how the oncogenic KRAS mutation inhibits the tumor suppressor FBW7, thus revealing an important function of KRAS mutations in promoting pancreatic cancer progression.

No abstract

We present 22 901 OB spectra of 16 032 stars identified from LAMOST DR5 dataset. A larger sample of OB candidates are firstly selected from the distributions in the spectral line indices space. Then all 22 901 OB spectra are identified by manual inspection. Based on a sub-sample validation, we find that the completeness of the OB spectra reaches about 89 ± 22% for the stars with spectral type earlier than B7, while around 57 ± 16% B8-B9 stars are identified. The smaller completeness for late B stars is lead to the difficulty to discriminate them from A0-A1 type stars. The sub-classes of the OB samples are determined using the software package MKCLASS. With a careful validation using 646 sub-samples, we find that MKCLASS can give fairly reliable sub-types and luminosity class for most of the OB stars. The uncertainty of the spectral sub-type is around 1 sub-type and the uncertainty of the luminosity class is around 1 level. However, about 40% of the OB stars are failed to be assigned to any class by MKCLASS and a few spectra are significantly misclassified by MKCLASS. This is likely because that the template spectra of MKCLASS are selected from nearby stars in the solar neighborhood, while the OB stars in this work are mostly located in the outer disk and may have lower metallicity. The rotation of the OB stars may also be responsible for the mis-classifications. Moreover, we find that the spectral and luminosity classes of the OB stars located in the Galactic latitude larger than 20 • are substantially different with those located in latitude smaller than 20 • , which may either due to the observational selection effect or hint a different origin of the high Galactic latitude OB stars.