Hypoxia regulates global membrane protein endocytosis through caveolin-1 in cancer cells.

Hypoxia promotes tumour aggressiveness and resistance of cancers to oncological treatment. The identification of cancer cell internalizing antigens for drug targeting to the hypoxic tumour niche remains a challenge of high clinical relevance. Here we show that hypoxia down-regulates the surface proteome at the global level and, more specifically, membrane proteome internalization. We find that hypoxic down-regulation of constitutive endocytosis is HIF-independent, and involves caveolin-1-mediated inhibition of dynamin-dependent, membrane raft endocytosis. Caveolin-1 overexpression inhibits protein internalization, suggesting a general negative regulatory role of caveolin-1 in endocytosis. In contrast to this global inhibitory effect, we identify several proteins that can override caveolin-1 negative regulation, exhibiting increased internalization at hypoxia. We demonstrate antibody-mediated cytotoxin delivery and killing specifically of hypoxic cells through one of these proteins, carbonic anhydrase IX. Our data reveal that caveolin-1 modulates cell-surface proteome turnover at hypoxia with potential implications for specific targeting of the hypoxic tumour microenvironment.

Overexpression of podocalyxin-like protein is an independent factor of poor prognosis in colorectal cancer.

BACKGROUND: Podocalyxin-like 1 (PODXL) is a cell-adhesion glycoprotein and stem cell marker that has been associated with an aggressive tumour phenotype and poor prognosis in several forms of cancer. In this study, we investigated the prognostic impact of PODXL expression in colorectal cancer (CRC). METHODS: Using tissue microarrays and immunohistochemistry, PODXL expression was evaluated in 536 incident CRC cases from a prospective, population-based cohort study. Kaplan-Meier analysis and Cox proportional hazards modelling were used to assess the impact of PODXL expression on cancer-specific survival (CSS) and overall survival (OS). RESULTS: High PODXL expression was significantly associated with unfavourable clinicopathological characteristics, a shorter CSS (hazard ratio (HR)=1.98; 95% confidence interval (CI) 1.38-2.84, P<0.001) and 5-year OS (HR=1.85; 95% CI 1.29-2.64, P=0.001); the latter remaining significant in multivariate analysis (HR=1.52; 95% CI 1.03-2.25, P=0.036). In addition, in curatively resected stage III (T1-4, N1-2, M0) patients (n=122) with tumours with high PODXL expression, a significant benefit from adjuvant chemotherapy was demonstrated (p(interaction) =0.004 for CSS and 0.015 for 5-year OS in multivariate analysis). CONCLUSION: Podocalyxin-like 1 expression is an independent factor of poor prognosis in CRC. Our results also suggest that PODXL may be a useful marker to stratify patients for adjuvant chemotherapy.

Identification of ubiquitin in bovine milk and its growth inhibitory effects on human cancer cell lines.

Bovine milk is associated with improved health and reduced risk of several diseases, among them cancer. Milk is a complex mixture of known and unknown components. The components and the mechanisms that contribute to the cancer-preventive effects are largely unknown. We set out to find new peptides in milk and identified ubiquitin (Ub) using matrix-assisted laser desorption ionization-time of flight mass spectrometry and Western blot. Using quantitative Western blot, we estimated the Ub concentration to be about 0.003 micromol/L in milk. We then decided to investigate the effect of treating human colon cancer CaCo-2 cells with Ub, using higher concentrations than in milk. CaCo-2 cells treated with 0.02 to 2.0 micromol/L Ub showed significantly decreased proliferation compared with untreated control cells. A higher growth inhibitory effect than in CaCo-2 cells was found in the neuroblastoma cell line SH-SY5Y treated with 0.02 to 0.2 micromol/L Ub. A bromodeoxyuridine DNA flow cytometric method was used to study cell cycle kinetics in Ub-treated CaCo-2 cells. The data point toward a prolongation of the G(1) phase. The levels of several cell cycle regulatory proteins were affected. Our data point to Ub possibly being one of the components in milk reducing the risk of cancer.

Identification of sequences in Epstein-Barr virus DNA required for the expression of the second Epstein-Barr virus-determined nuclear antigen in COS-1 cells.

The BamHI WYH region of the Epstein-Barr virus (EBV) genome encodes a protein localized to the nucleus of the infected cell, the EBV-determined nuclear antigen EBNA2. We have constructed a series of recombinant vectors that carried the complete EBNA2 gene, or the gene modified so as to contain defined deletions involving presumed exons and regulatory elements of the gene. The recombinant vectors were transfected into COS-1 cells which permit the replication of simian virus 40 origin-containing plasmids to a high copy number, and the transient expression of EBNA2 was analysed. A recombinant plasmid that carried a BglII-NotI subfragment of the BamHI WYH region (nucleotides 44664 to 50628) contained all the information necessary for inducing the expression of a full length EBNA2 polypeptide. Moreover, EBV DNA sequences between nucleotides 45,442 and 48,337 could be deleted without interfering with the ability of the vectors to induce EBNA2. On the other hand the loss of the left one-third of the BglII-NotI fragment completely abolished the EBNA2-inducing capacity of the vector. A rightward promoter consensus sequence in the BamHI W part of the BglII-NotI fragment was functional in COS-1 cells expressing EBNA2 and essential for EBV-specific RNA synthesis. The results indicated that transcription of the EBNA2 gene was initiated in the BamHI W fragment, that the transcript was spliced and that all of EBNA2 was encoded within the continuous long open reading frame in the BamHI Y and H fragments.

Stable transfection of a human lymphoma line by sub-genomic fragments of Epstein-Barr virus DNA to measure humoral and cellular immunity to the corresponding proteins.

An Epstein-Barr virus (EBV)-negative human lymphoid B-cell line, DG75, was stably transfected with recombinant selection vectors that carry a subfragment of the BamHI WYH region (nucleotides 44664 to 50628), the BamHI K fragment, or a subfragment of the EcoRI D region (nucleotides 166614 to 170149) of B95-8 EBV DNA. These fragments contain the coding exons for the EBV-determined nuclear antigens EBNA2 and EBNA1, and the membrane antigen LMP, respectively. Antigen expression of the cells was detected by immunofluorescence. EBNA2 was expressed in 80-100% of the transfected cells, in contrast to EBNA1 which was expressed in only 25%, and LMP in only about 5% of the cells. Humoral antibody responses were measured by immunofluorescence and compared to cellular immunity as determined by the leukocyte migration inhibition (LMI) technique. Extracts from transfected cell lines expressing EBNA1, EBNA2 or LMP elicited an LMI response with cells from healthy EBV-seropositive individuals whereas the extract from the parental DG75 cell line did not. The results demonstrate the value of stably transfected cell lines expressing a defined EBV antigen for the monospecific analysis of host responses to the EBV-encoded antigen complex in growth-transformed cells.