BACKGROUND: Despite earlier studies demonstrating in vitro propagation of solid tumour cancer stem cells (CSCs) as non-adherent tumour spheres, it remains controversial as to whether CSCs can be maintained in vitro. Additional validation of the CSC properties of tumour spheres would support their use as CSC models and provide an opportunity to discover additional CSC cell surface markers to aid in CSC detection and potential elimination. METHODS: Primary tumour cells isolated from 13 surgically resected colon tumour specimens were propagated using serum-free CSCselective conditions. The CSC properties of long-term cultured tumour spheres were established and mass spectrometry-based proteomics performed. RESULTS: Freshly isolated CD133 þ colorectal cancer cells gave rise to long-term tumour sphere (or spheroids) cultures maintaining CD133 expression. These spheroid cells were able to self-renew and differentiate into adherent epithelial lineages and recapitulate the phenotype of the original tumour. Relative to their differentiated progeny, tumour spheroid cells were more resistant to the chemotherapeutic irinotecan. Finally, CD44, CD166, CD29, CEACAM5, cadherin 17, and biglycan were identified by mass spectrometry to be enriched in CD133 þ tumour spheroid cells. CONCLUSION: Our data suggest that ex vivo-expanded colon CSCs isolated from clinical specimens can be maintained in culture enabling the identification of CSC cell surface-associated proteins.

ExperimentalBattery construction.-Batteries were assembled in hermetically sealed stainless steel cans with a lithium metal anode and an elec-

RNA processing is altered during malignant transformation, and expression of the polypyrimidine tract-binding protein (PTB) is often increased in cancer cells. Although some data support that PTB promotes cancer, the functional contribution of PTB to the malignant phenotype remains to be clarified. Here we report that although PTB levels are generally increased in cancer cell lines from multiple origins and in endometrial adenocarcinoma tumors, there appears to be no correlation between PTB levels and disease severity or metastatic capacity. The three isoforms of PTB increase heterogeneously among different tumor cells. PTB knockdown in transformed cells by small interfering RNA decreases cellular growth in monolayer culture and to a greater extent in semi-solid media without inducing apoptosis. Down-regulation of PTB expression in a normal cell line reduces proliferation even more significantly. Reduction of PTB inhibits the invasive behavior of two cancer cell lines in Matrigel invasion assays but enhances the invasive behavior of another. At the molecular level, PTB in various cell lines differentially affects the alternative splicing pattern of the same substrates, such as caspase 2. Furthermore, overexpression of PTB does not enhance proliferation, anchorage-independent growth, or invasion in immortalized or normal cells. These data demonstrate that PTB is not oncogenic and can either promote or antagonize a malignant trait dependent upon the specific intra-cellular environment.The polypyrimidine tract-binding protein (PTB), 3 also termed heterogeneous nuclear ribonucleoprotein I, is a 57-kDa RNA-binding protein that binds preferentially to pyrimidinerich sequences (1-3). PTB contains four RNA recognition motifs (RRMs). RRM 1 and 2 at the N terminus of the protein are involved in the dimerization of PTB, whereas RRM 3 and 4 are responsible for high affinity interactions with RNA (4, 5). PTB has been shown to be involved in many aspects of pre-mRNA and mRNA metabolism. PTB participates in pre-mRNA splicing (6) and acts as a splicing repressor in alternative splicing of pre-mRNA (5, 7-12). PTB is also involved in 3Ј end polyadenylation of pre-mRNA (13-15) and is important for translational regulation of certain RNA transcripts through internal ribosome entry sites (16 -20). In addition, PTB shuttles between the nucleus and the cytoplasm (21), which is regulated through phosphorylation by 3Ј,5Ј-cAMP-dependent protein kinase (22).Alternative splicing is a process that allows multiple different proteins to be made from the same pre-mRNA by either including or excluding particular exons during pre-mRNA splicing. PTB plays a key role in alternative site selection for many gene products by acting as a splicing repressor that prevents the inclusion of target exons (11,(23)(24)(25). Changes in alternative splicing sites have been previously correlated with malignant transformation (26 -29), and the expression level of PTB has been found elevated in transformed cells. Such an elevation is responsible for the increases...

The perinucleolar compartment (PNC) is a nuclear subdomain that is unique to tumor cells, and the percentage of cells in a population containing PNCs (PNC prevalence) indicates the level of malignancy of that population. Here, we utilize anticancer drugs and other exogenous stimuli to investigate the structure and function of the PNC. Screening of clinically used anti-cancer drugs revealed two types of drugs disassemble PNCs and do so through their specific molecular actions. Transcription inhibitors reduce PNC prevalence in parallel with RNA polymerase III transcription reduction, and a subset of DNA-damaging drugs and stimuli (UV radiation) disassemble the PNC. Inhibition of cellular DNA damage response demonstrated that the DNA damage itself, not the response or polymerase III inhibition, is responsible for PNC disassembly, suggesting that the maintenance of the PNC is dependent upon DNA integrity. Analyses of the types of DNA damage that cause PNC disassembly show that interstrand DNA base pairing, not strand continuity, is important for PNC integrity, indicating that the PNC components are directly interacting with the DNA. Complementary cell biology experiments demonstrated that the number of PNCs per cell increases with the rounds of endoreplication and that PNCs split into doublets during mid S phase, both of which are phenotypes that are typical of a replicating DNA loci. Together, these studies validate PNC disassembly as a screening marker to identify chemical probes and revealed that the PNC is directly nucleated on a DNA locus, suggesting a potential role for the PNC in gene expression regulation. The perinucleolar compartment (PNC)2 is a non-membrane-bound nuclear subdomain that is associated with, but structurally distinct from, the nucleolus. The PNC is a generally heritable trait, in which the number of PNCs per cell in daughter cells often mimics that of their mother cells. The PNC is heterogeneous in shape and ranges from 0.5 to 4 m in size (1), is stable through interphase, disassembles during mitosis, and reassembles in early G 1 (1). The PNC is concentrated with newly synthesized RNA polymerase III RNAs (MRP RNase RNA, RNase P H1 RNA, hY RNAs (hY1, -2, and -5), AluRNA, and SRP (7SL) RNA) and RNA-binding proteins (nucleolin, PTB, CUG repeat-binding protein, KSRP, Raver1, Raver2, and Rod1) (2-9).3 Continuous transcription by pol III is necessary for the structure integrity of the PNC, implicating involvement of PNCs in pol III RNA metabolism (9). However, the complete molecular composition and function of the PNC remain to be elucidated.Extensive in vitro studies showed that the PNC is unique to tumor cells and preferentially forms in tumor cells derived from solid tissues (1, 10). In vitro studies of cancer cell lines from various origins and malignant capacities have shown that PNC prevalence correlates with the malignancy of tumors and has the potential to be developed as a pan-cancer prognostic marker (10). In addition, in vivo investigations using human breast tissue samples demonstrated...

Metastasis remains a leading cause of cancer mortality due to the lack of specific inhibitors against this complex process. To identify compounds selectively targeting the metastatic state, we used the perinuclear compartment (PNC), a complex nuclear structure associated with metastatic behaviors of cancer cells, as a phenotypic marker for a high-content screen of over 140,000 structurally diverse compounds. Metarrestin, obtained through optimization of a screening hit, disassembles PNCs in multiple cancer cell lines, inhibits invasion in vitro, blocks metastatic development in three mouse models of human cancer, and extends survival of mice in a metastatic pancreatic cancer xenograft model with no organ toxicity or discernable adverse effects. Metarrestin disrupts the nucleolar structure and inhibits RNA polymerase (Pol) I transcription, at least in part by interacting with the translation elongation factor eEF1A2. Altogether, metarrestin represents a potential therapeutic approach for the treatment of metastatic cancer.