(Santa Cruz, USA) were used in the study. XAV-939 purchase Cell lines and culture conditions The human breast cancer cell line MDA-MB-231 was routinely maintained
in Dulbecco’s Modified Eagle Medium (DMEM) (Sigma-Aldrich, Dorset, UK) supplemented with 10% fetal calf serum (FCS), penicillin and streptomycin (Sigma-Aldrich, Dorset, UK). The cells were incubated at 37°C, 5% CO2 and 95% humidity. Human breast specimens A total of 133 breast samples were obtained from breast cancer patients (106 breast cancer tissues and 27 associated background or related normal tissue), with the consent of the patients and approved by the ethical committee. The pathologist verified normal background and cancer specimens, PD-1/PD-L1 inhibitor and it was confirmed that the background samples were free from tumour deposit. These tissues after mastectomy were immediately frozen in liquid nitrogen. Over-expression of Claudin-5 in MDA-MB-231 breast cancer cells A range of normal human tissues were screened for Claudin-5. Normal placenta tissue was chosen for endogenous expression of Claudin-5. The human breast cancer cell line MDA-MB-231was chosen for introduction of
the Claudin-5 gene. The gene, after amplification from placenta tissue cDNA was cloned into aPEF6/V5-His TOPO TA plasmid vector (Invitrogen Ltd., Paisley, UK) breast cancer cells or MDA-MB-231. Expression of the gene was confirmed by RT-PCR. The Claudin-5 expression construct and empty plasmid were, respectively, used to transfect MDA-MB-231 cells by electroporation. Stably transfected cells were then used for subsequent assays after being tested at both transcriptional and translational level. Those cells containing the expression plasmid and displaying enhanced Claudin-5 expression were designated MDA-MB-231CL5exp/MDACL5exp,
those containing the closed pEF6 empty plasmid and used as control cells were designated MDA-MB-231pEF6/MDApEF6 and unaltered wild type 5-FU in vitro were designated MDA-MB-231WT/MDAWT. Generation of Claudin-5 ribozyme transgenes Antihuman Claudin-5 hammerhead ribozymes were designed based on the predictive secondary mRNA structure using Zuker’s RNA mFold program as previously reported [23]. Those knockdown cells displaying low levels of Claudin-5 were designated MDA-MB-231CL5rib2/MDACL5rib2. RNA extraction and Reverse Transcription-Polymerase Chain Reaction (RT-PCR) Cells were grown to confluence in a 25 cm3 flask before RNA was extracted using total RNA isolation (TRI) reagent and following the protocol provided (Sigma-Aldrich, Dorset, UK). RNA was converted to cDNA using iScript cDNA synthesis kit (Primer Desing Ltd., Southampton, UK). Following cDNA synthesis, samples were probed using actin primers to check the quality of the cDNA and confirm uniform levels within each sample together with those specific for the Claudin-5 transcript (full primer sequences are outline in Table 1).