BackgroundCancer stem cells (CSCs) are regarded as the cause of tumor formation and recurrence. The isolation and identification of CSCs could help to develop novel therapeutic strategies specifically targeting CSCs.MethodsHuman hepatoma cell lines were plated in stem cell conditioned culture system allowed for sphere forming. To evaluate the stemness characteristics of spheres, the self-renewal, proliferation, chemoresistance, tumorigenicity of the PLC/PRF/5 sphere-forming cells, and the expression levels of stem cell related proteins in the PLC/PRF/5 sphere-forming cells were assessed, comparing with the parental cells. The stem cell RT-PCR array was performed to further explore the biological properties of liver CSCs.ResultsThe PLC/PRF/5, MHCC97H and HepG2 cells could form clonal nonadherent 3-D spheres and be serially passaged. The PLC/PRF/5 sphere-forming cells possessed a key criteria that define CSCs: persistent self-renewal, extensive proliferation, drug resistance, overexpression of liver CSCs related proteins (Oct3/4, OV6, EpCAM, CD133 and CD44). Even 500 sphere-forming cells were able to form tumors in NOD/SCID mice, and the tumor initiating capability was not decreased when spheres were passaged. Besides, downstream proteins DTX1 and Ep300 of the CSL (CBF1 in humans, Suppressor of hairless in Drosophila and LAG1 in C. elegans) -independent Notch signaling pathway were highly expressed in the spheres, and a gamma-secretase inhibitor MRK003 could significantly inhibit the sphere formation ability.ConclusionsNonadherent tumor spheres from hepatoma cell lines cultured in stem cell conditioned medium possess liver CSC properties, and the CSL-independent Notch signaling pathway may play a role in liver CSCs.
Abstract. 14-3-3 is a ubiquitous protein family that in-
. Our results demonstrate a unique K18 phosphorylation site that is necessary but not sufficient for K18 binding to 14-3-3 proteins. This binding is likely to involve one or more mitotic events coupled to K18 Ser33 phosphorylation, and plays a role in keratin subcellular distribution. Physiological Ser52 or Ser33 phosphorylation on distinct K18 molecules suggests functional compartmentalization of these modifications.
Type I and II keratins help maintain the structural integrity of epithelial cells. Since apoptosis involves progressive cell breakdown, we examined its effect on human keratin polypeptides 8, 18, and 19 (K8, K18, K19) that are expressed in simple-type epithelia as noncovalent type I (K18, K19) and type II (K8) heteropolymers. Apoptosis induces rapid hyperphosphorylation of most known K8/18 phosphorylation sites and delayed formation of K18 and K19 stable fragments. In contrast, K8 is resistant to proteolysis and remains associated with the K18 fragments. Transfection of phosphorylation/glycosylation-mutant K8 and K18 does not alter fragment formation. The protein domains of the keratin fragments were determined using epitope-defined antibodies, and microsequencing indicated that K18 cleavage occurs at a conserved caspase-specific aspartic acid. The fragments are found preferentially within the detergentinsoluble pool and can be generated, in a phosphorylation-independent manner, by incubating keratins with caspase-3 or with detergent lysates of apoptotic cells but not with lysates of nonapoptotic cells. Our results indicate that type I keratins are targets of apoptosis-activated caspases, which is likely a general feature of keratins in most if not all epithelial cells undergoing apoptosis. Keratin hyperphosphorylation occurs early but does not render the keratins better substrates of the downstream caspases. Intermediate filament (IF)1 proteins encompass the nuclear lamins and a large family of tissue-specific cytoplasmic proteins that include keratins in epithelial cells, desmin in muscle, neurofilaments in neuronal cells, and vimentin in mesenchymal cells (reviewed in Refs. 1-3). Keratins are the largest IF protein subgroup and consist of more than 20 polypeptides (K1-K20) that are divided into relatively acidic type I (K9 -K20) and basic type II (K1-K8) keratins (4, 5). All epithelial cells typically express at least one type I and one type II keratin, as noncovalent obligate heteropolymers, in an epithelial cell-type specific manner. For example, simple-type epithelia preferentially express K8/18 with various levels of K19 and K20 (6 -10), keratinocytes express K1/10 and/or K5/14 depending on their differentiation state within the epidermal layer, and corneal epithelial cells express K3/12 (4). Although the full scope of keratin function is not known, one clear keratin function is to help maintain epithelial cell integrity particularly upon cell stress. This role is supported by several animal studies and a growing list of human epidermal, oral, and ocular diseases that result from keratin mutations (11-16).Keratins undergo several modifications that are likely involved in regulating their function (reviewed in Ref. 17), with phosphorylation being the most studied (reviewed in 18, 19). For K8/18, the known in vivo phosphorylation sites include Ser-52/Ser-33 of K18 (20) 2 and Ser-23/Ser-431/Ser-73 of K8 (22, 23). Of note, keratin phosphorylation is highly dynamic (24 -27) and is modulated during several phy...
The p53 tumor suppressor protein and the MDM2 oncoprotein form a feedback-control loop that up-regulates cellular MDM2 production, blocks p53 activity, and promotes p53 decay. tsg101 was discovered as a gene whose deficiency results in neoplastic transformation of NIH 3T3 cells and the ability to generate metastatic tumors in nude mice. Its protein product contains a domain, Ubc, characteristic of the catalytic domain of ubiquitin conjugase (E2) enzymes but lacking an active-site cysteine crucial for ubiquitin conjugase activity. Here we report that TSG101 participates with MDM2 in an autoregulatory loop that modulates the cellular levels of both proteins, and also of p53, by affecting protein decay. We show that the Ubc domain of TSG101 interferes with ubiquitination of MDM2, that TSG101 inhibits MDM2 decay and elevates its steady-state level, and that these events are associated with down-regulation of p53 protein. Conversely, pulse-chase and Western blot experiments in wild-type and mutant fibroblasts indicate that elevation of MDM2 by overexpression of wild-type p53, by amplification of the endogenous MDM2 gene, or by transfection of MDM2-expressing constructs promotes TSG101 loss, which we show occurs by 26S proteasome-dependent decay. Our results identify TSG101 as both a regulator of, and target of, MDM2͞p53 circuitry.tumorigenesis ͉ ubiquitination ͉ proteolysis
Purpose: To establish a sensitive and specific isolation and enumeration system for circulating tumor cells (CTC) in patients with hepatocellular carcinoma (HCC).Experimental Design: HCC cells were bound by biotinylated asialofetuin, a ligand of asialoglycoprotein receptor, and subsequently magnetically labeled by antibiotin antibody-coated magnetic beads, followed by magnetic separation. Isolated HCC cells were identified by immunofluorescence staining using Hep Par 1 antibody. The system was used to detect CTCs in 5 mL blood. Blood samples spiked with Hep3B cells (ranging from 10 to 810 cells) were used to determine recovery and sensitivity. Prevalence of CTCs was examined in samples from HCC patients, healthy volunteers, and patients with benign liver diseases or non-HCC cancers. CTC samples were also analyzed by FISH.Results: The average recovery was 61% or more at each spiking level. No healthy, benign liver disease or non-HCC cancer subjects had CTCs detected. CTCs were identified in 69 of 85 (81%) HCC patients, with an average of 19 AE 24 CTCs per 5 mL. Both the positivity rate and the number of CTCs were significantly correlated with tumor size, portal vein tumor thrombus, differentiation status, and the disease extent as classified by the TNM (tumor-node-metastasis) classification and the Milan criteria. HER-2 gene amplification and TP53 gene deletion were detected in CTCs.Conclusion: Our system provides a new tool allowing for highly sensitive and specific detection and genetic analysis of CTCs in HCC patients. It is likely clinically useful in diagnosis and monitoring of HCC and may have a role in clinical decision making.
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