Cartilage Tissue Engineering by the 3D Bioprinting of iPS Cells in a Nanocellulose/Alginate Bioink.

Cartilage lesions can progress into secondary osteoarthritis and cause severe clinical problems in numerous patients. As a prospective treatment of such lesions, human-derived induced pluripotent stem cells (iPSCs) were shown to be 3D bioprinted into cartilage mimics using a nanofibrillated cellulose (NFC) composite bioink when co-printed with irradiated human chondrocytes. Two bioinks were investigated: NFC with alginate (NFC/A) or hyaluronic acid (NFC/HA). Low proliferation and phenotypic changes away from pluripotency were seen in the case of NFC/HA. However, in the case of the 3D-bioprinted NFC/A (60/40, dry weight % ratio) constructs, pluripotency was initially maintained, and after five weeks, hyaline-like cartilaginous tissue with collagen type II expression and lacking tumorigenic Oct4 expression was observed in 3D -bioprinted NFC/A (60/40, dry weight % relation) constructs. Moreover, a marked increase in cell number within the cartilaginous tissue was detected by 2-photon fluorescence microscopy, indicating the importance of high cell densities in the pursuit of achieving good survival after printing. We conclude that NFC/A bioink is suitable for bioprinting iPSCs to support cartilage production in co-cultures with irradiated chondrocytes.

E2F1, ARID3A/Bright and Oct-2 factors bind to the Epstein-Barr virus C promoter, EBNA1 and oriP, participating in long-distance promoter-enhancer interactions.

The Epstein-Barr virus (EBV) C promoter (Cp) regulates several genes required for B-cell proliferation in latent EBV infection. The family of repeats (FR) region of the latent origin of plasmid replication (oriP) functions as an Epstein-Barr nuclear antigen 1 (EBNA1)-dependent distant enhancer of Cp activity, and the enhancer-promoter interaction is mediated by a higher-order multi-protein complex containing several copies of EBNA1. Using DNA-affinity purification with a 170 bp region of the Cp in combination with mass spectrometry, we identified the cell cycle-regulatory protein E2F1, the E2F-binding protein ARID3A, and the B-cell-specific transcription factor Oct-2 as components of this multi-protein complex. Binding of the three factors to the FR region of oriP was determined by DNA-affinity and immunoblot analysis. Co-immunoprecipitation and proximity ligation analysis revealed that the three factors, E2F1, ARID3A and Oct-2, interact with each other as well as with EBNA1 in the nuclei of EBV-positive cells. Using the chromatin immunoprecipitation assay, we showed that E2F1 and Oct-2 interacted with the FR part of oriP and the Cp, but the ARID3A interaction was, however, only detected at the Cp. Our findings support the hypothesis that EBNA1 initiates transcription at the Cp via interactions between multiple EBNA1 homodimers and cellular transcription factors in a large molecular machinery that forms a dynamic interaction between Cp and FR.

Identification of intracellular proteins associated with the EBV-encoded nuclear antigen 5 using an efficient TAP procedure and FT-ICR mass spectrometry.

Epstein-Barr virus nuclear antigen 5 (EBNA5) is one of the first viral proteins detected after primary EBV infection and has been shown to be required for efficient transformation of B lymphocytes. EBNA5 is a protein that has many suggested functions but the underlying biology remains to be clarified. To gain further insight into the biological roles of the proposed multifunctional EBNA5, we isolated EBNA5 containing protein complexes using a modified tandem affinity purification (TAP) method and identified the protein components by LC-MS/MS analysis of tryptic digests on a LTQ-FT-ICR mass spectrometer. The modified TAP tag contained a Protein A domain and a StrepTagII sequence separated by two Tobacco Etch Virus protease cleavage sites and was fused to the C-terminus of EBNA5. Our results confirmed the wide applicability of this two-step affinity purification strategy for purification of protein complexes in mammalian cells. A total of 147 novel putative EBNA5 interaction partners were identified, 37 of which were validated with LC-MS/MS in split-tag experiments or in co-immuno precipitates from HEK293 cell extracts. This subgroup included the Bcl2-associated Athanogene 2 (BAG2) co-chaperone involved in protein folding and renaturation, the 26S proteasome subunit 2 involved in regulation of ubiquitin/proteasome protein degradation, and the heterogeneous ribonucleoprotein M (hnRNP M) involved in pre-mRNA processing. These EBNA5 interactors were further verified by co-immunoprecipitations from cell extracts of three EBV-positive lymphoblastoid lines. The combination of the Hsp70, Hsc70, BAG2 and 26S proteasome subunit 2 interactors suggests that EBNA5 might have a functional relationship with protein quality control systems that recognize proteins with abnormal structures and either refold them to normal conformation or target them for degradation. Our study also confirms previously identified interactors including HA95, Hsp70, Hsc70, Hsp27, HAX-1, Prolyl 4-hydroxylase, S3a, and alpha- and beta-tubulin.