👤 Jung-Min Lee

Epidermal growth factor (EGF) induces cell proliferation in a variety of cell types by binding to a prototype transmembrane tyrosine kinase receptor. Ligation of this receptor by EGF activates Erk1 and Erk2, members of the mitogen-activated protein (MAP) kinase family, through a Ras-dependent signal transduction pathway. Despite our detailed understanding of these events, the exact mechanism by which EGF causes cells to proliferate is unclear. Big MAP kinase (Bmk1), also known as Erk5, is a member of the MAP kinase family that is activated in cells in response to oxidative stress, hyperosmolarity and treatment with serum. Here we show that EGF is a potent activator of Bmk1. In contrast to Erk1/2, EGF-mediated activation of Bmk1 occurs independently of Ras and requires the MAP-kinase kinase Mek5. Expression of a dominant-negative form of Bmk1 blocks EGF-induced cell proliferation and prevents cells from entering the S phase of the cell cycle. These results demonstrate that Bmk1 is part of a distinct MAP-kinase signalling pathway that is required for EGF-induced cell proliferation and progression through the cell cycle. Show less

Mutations at the mouse Fused locus have pleiotropic developmental effects, including the formation of axial duplications in homozygous embryos. The product of the Fused locus, Axin, displays similarities to RGS (Regulators of G-Protein Signaling) and Dishevelled proteins. Mutant Fused alleles that cause axial duplications disrupt the major mRNA, suggesting that Axin negatively regulates the response to an axis-inducing signal. Injection of Axin mRNA into Xenopus embryos inhibits dorsal axis formation by interfering with signaling through the Wnt pathway. Furthermore, ventral injection of an Axin mRNA lacking the RGS domain induces an ectopic axis, apparently through a dominant-negative mechanism. Thus, Axin is a novel inhibitor of Wnt signaling and regulates an early step in embryonic axis formation in mammals and amphibians. Show less

In budding yeast, entry into the mitotic cell cycle, or Start, requires the Cdc28 cyclin-dependent kinase (Cdk) and one of its three associated G1 cyclins, Cln1, Cln2, or Cln3. In addition, two other G1 cyclins, Pcl1 and Pcl2, associate with a second Cdk, Pho85, to contribute to Start. Although Pho85 is not essential for viability, Pcl1,2-Pho85 kinase complexes become essential for Start in the absence of Cln1,2-Cdc28 kinases. In addition, Pho85 interacts with a third cyclin, Pho80, to regulate acid phosphatase gene expression. Other cellular roles for Pho85 cyclin-Cdk complexes are suggested by the multiple phenotypes associated with deletion of PHO85, in addition to Start defects and deregulated acid phosphatase gene expression. Strains with pho80, pcl1, and pcl2 deletions show only a subset of the pho85 mutant phenotypes, suggesting the existence of additional Pho85 cyclins (Pcls). We used two-hybrid screening and database searching to identify seven additional cyclin-related genes that may interact with Pho85. We found that all of the new genes encode proteins that interacted with Pho85 in an affinity chromatography assay. One of these genes, CLG1, was previously suggested to encode a cyclin, based on the protein's sequence homology to Pcl1 and Pcl2. We have named the other genes PCL5, PCL6, PCL7, PCL8, PCL9, and PCL10. On the basis of sequence similarities, the PCLs can be divided into two subfamilies: the Pcl1,2-like subfamily and the Pho80-like subfamily. We found that deletion of members of the Pcl1,2 class of genes resulted in pronounced morphological abnormalities. In addition, we found that expression of one member of the Pcl1,2 subfamily, PCL9, is cell cycle regulated and is decreased in cells arrested in G1 by pheromone treatment. Our studies suggest that Pho85 associates with multiple cyclins and that subsets of cyclins may direct Pho85 to perform distinct roles in cell growth and division. Show less

Hepatocellular carcinoma (HCC) is one of the most common human tumors in Asia and Africa. The molecular genetic changes involving both protooncogenes and tumor suppressor genes are known to be involved in hepatocarcinogenesis, but the roles of the known tumor suppressor genes in hepatocarcinogenesis are not fully elucidated. In this study, the authors analyzed the loss of heterozygosity (LOH) of known tumor suppressor genes in HCC and evaluated the relationship between LOH of tumor suppressor genes and clinicopathologic features. The authors assessed the LOH of the 10 known tumor suppressor genes (VHL, APC, EXT1, WT1, Rb1, p53, BRCA1, nm23, DPC4, and DCC) with microsatellite markers in 29 consecutively resected HCC specimens. The authors found frequent LOH of tumor suppressor genes in HCC. Twenty five of 29 cases (86%) had LOH of tumor suppressor genes and 17 cases (59%) had LOHs involving 2-4 tumor suppressor genes. Among the tumor suppressor genes, frequent LOH was noted in the p53 (66%), Rb1 (33%), EXT1 (33%), and APC (20%) genes. LOH of the p53 gene and multiple LOH of the tumor suppressor genes were more frequent in poorly differentiated HCCs (P = 0.02). The LOH of tumor suppressor genes is frequent in HCCs and LOH of the p53 gene and accumulated LOHs are related to poorly differentiated HCC. Abnormalities of the p53 gene or the accumulated abnormalities of the tumor suppressor genes may play a role in the aggressive progression of HCC. Show less

Big MAP kinase 1 (BMK1), also known as ERK5, is a mitogen-activated protein (MAP) kinase member whose biological role is largely undefined. We have shown previously that the activity of BMK1 in rat smooth muscle cells is up-regulated by oxidants. Here, we describe a constitutively active form of the MAP kinase kinase, MEK5(D), which selectively activates BMK1 but not other MAP kinases in vivo. Through utilization of MEK5(D), we have determined that a member of the MEF2 transcription factor family, MEF2C, is a protein substrate of BMK1. BMK1 dramatically enhances the transactivation activity of MEF2C by phosphorylating a serine residue at amino acid position 387 in this transcription factor. Serum is also a potent stimulator of BMK1-induced MEF2C phosphorylation, since a dominant-negative form of BMK1 specifically inhibits serum-induced activation of MEF2C. One consequence of MEF2C activation is increased transcription of the c-jun gene. Taken together, these results strongly suggest that in some cell types the MEK5/BMK1 MAP kinase signaling pathway regulates serum-induced early gene expression through the transcription factor MEF2C. Show less

Saccharomyces cerevisiae, which lack a functional SOD1 gene, encoding the cytosolic Cu,Zn-superoxide dismutase (SOD1), exhibit a variety of metabolic defects in aerobic but not in anaerobic growth. We test here the hypothesis that some of these defects may be due to specific transcriptional changes programmed for cell survival under dioxygen stress. Analysis of the budding pattern and generation time showed that the slower proliferation of an sod1Delta mutant strain under air was due to an increase from 42 to 89 min spent in the G1 phase of the cell cycle. This delay in G1 was not due to an overall decline in biosynthetic activity since total protein and mRNA synthesis was not reduced even under 100% O2. However, rRNA synthesis was strongly decreased, e.g. by 80% in the mutant under 100% O2 (in comparison to N2). Under these conditions, the mutant permanently arrested in G1; this arrest was due to an inhibition of the Start function that prepares yeast for S phase. This Start arrest was due to an inhibition of transcription of the autoregulated G1 cyclins, CLN1 and CLN2; the transcription of the constitutive G1 cyclin, CLN3, was unaffected by the stress. Expression of a hyperstable Cln3 prevented the G1 arrest, indicating that it was due solely to the inhibition of cell cycle-dependent cyclin expression. This remodeling of transcription in oxidative stress was seen also in the inhibition of glucose derepression of SUC2 expression. In contrast, the signaling and activation of mating pheromone (FUS1) and copper-responsive (CUP1) promoter activity were not affected by dioxygen stress, while genes encoding other anti-oxidant enzymes (SOD2, CTT1 and CTA1) were strongly induced. The UBI loci, encoding ubiquitin, were particularly good examples of this pattern of negative and positive transcriptional response to the stress. UBI1-UBI3 expression was repressed in the mutant under 100% O2, while expression of UBI4 was strongly induced. The data demonstrate that extensive remodeling of transcription occurs in yeast under a strong dioxygen stress. This remodeling results in a pattern of expression of gene products needed for defense and repair, and suppression of activities associated with normal proliferative growth. Show less

We describe the isolation and chromosomal mapping of a mouse homolog of the Batten disease gene, CLN3. Like its human counterpart, the mouse cDNA contains an open reading frame of 1314 bp encoding a predicted protein product of 438 amino acids. The mouse and human coding regions are 82 and 85% identical at the nucleic acid and amino acid levels, respectively. The mouse gene maps to distal Chromosome 7, in a region containing genes whose homologs are on human chromosome 16p12, where CLN3 maps. Isolation of a mouse CLN3 homolog will facilitate the creation of a mouse model of Batten disease. Show less

Hereditary multiple exostoses is an autosomal dominant disorder that is characterized by short stature and multiple, benign bone tumours. In a majority of families, the genetic defect (EXT1) is linked to the Langer-Giedion syndrome chromosomal region in 8q24.1. From this region we have cloned and characterized a cDNA which spans chromosomal breakpoints previously identified in two multiple exostoses patients. Furthermore, the gene harbours frameshift mutations in affected members of two EXT1 families. The cDNA has a coding region of 2,238 bp with no apparent homology to other known gene sequences and thus its function remains elusive. However, recent studies in sporadic and exostosis-derived chondrosarcomas suggest that the 8q24.1-encoded EXT1 gene may have tumour suppressor function. Show less

The cDNAs encoding human prostatic acid phosphatase were cloned and characterized. The mRNAs contain 3' noncoding regions of heterogeneous sizes 646, 1887 or 1913 nucleotides. A dimer and a monomer of the conserved Alu-repeats are present in the longer 3' noncoding sequences. The complete sequence of 354 amino acids for the mature enzyme was determined by sequencing both cDNA and protein. Human prostatic and lysosomal acid phosphatases exhibit 50% sequence homology, including five Cys residues and two putative N-linked glycosylation sites. The Acp-3 gene coding for human prostatic acid phosphatase was mapped onto chromosome 3 in this investigation. The Acp-2 gene coding for lysosomal acid phosphatase has previously been located on chromosome 11, while the Acp-1 gene coding for red blood cell acid phosphatase is on chromosome 2. Show less

A monoclonal antibody with high affinity to acid phosphatase isoenzyme 2 (Ab-AcP2) was selected to examine its binding to different normal and tumor tissues using the indirect immunohistochemical method. Both mature prostatic epithelial cells in the prostate and the highly dedifferentiated prostatic cancer cells in the bone marrow showed strong binding to the antibody. Among nonprostatic tissues, only bone marrow, breast, and kidney showed trace staining in some specimens. The specificity of Ab-AcP2 was much better than that of the polyclonal antibody to acid phospatase previously reported. When the antibody to the prostate-specific antigen (Ab-PSA) was used, weak background staining was often encountered, and weak to moderate stains were seen in the prostatic stroma, bone marrow, lung, skin, and melanoma. Show less