Factor VIII with a 237 amino acid B-domain has an extended half-life in F8-knockout mice.

Essentials Factor (F)VIII with an intermediate-length B-domain showed higher levels in murine gene therapy. FVIII with different B-domain lengths were analysed. FVIII variants with B-domains between 186 and 240 amino acids (aa) have extended half-life in mice. Reduced cell binding of FVIII with a 237aa B-domain may explain the extended half-life. SUMMARY: Background Factor VIII consists of the A1-domain, A2-domain, B-domain, A3-domain, C1-domain, and C2-domain. FVIII with an intermediate-length B-domain of 226 amino acids (aa) has previously been evaluated in murine gene therapy studies. Objective To characterize FVIII with intermediate-length B-domains in vitro and in vivo in F8-knockout (KO) mice. Methods and results FVIII molecules with B-domains of 186-240aa had longer half-lives in F8-KO mice than FVIII molecules with shorter or longer B-domains. FVIII with a B-domain containing the 225 N-terminal aa fused to the 12 C-terminal aa of the wild-type B-domain (FVIII-237) had a 1.6-fold extended half-life in F8-KO mice as compared with FVIII with a 21aa B-domain (FVIII-21). The in vitro and in vivo activity of FVIII-237 were comparable to those of FVIII-21, as was binding to von Willebrand factor. Cell binding to LDL receptor-related protein 1 (LRP-1)-expressing cells was markedly reduced for FVIII-237 as compared with FVIII-21, whereas the affinity for LRP-1 was not reduced in surface plasmon resonance (SPR) studies. FVIII-21 cell binding and internalization could be inhibited by a fragment consisting of the 226 N-terminal aa of the FVIII B-domain, and SPR analysis suggested that this B-domain fragment might bind with weak affinity to FVIII-21. Conclusion Reduced cell binding of FVIII-237 might explain the observed extended half-life in F8-KO mice. This may contribute to the increased FVIII levels measured in murine gene therapy studies using FVIII constructs with similar B-domain lengths.

Purification and characterization of a new recombinant factor VIII (N8).

SUMMARY: A new recombinant factor VIII (FVIII), N8, has been produced in Chinese hamster ovary (CHO) cells. The molecule consists of a heavy chain of 88 kDa including a 21 amino acid residue truncated B-domain and a light chain of 79 kDa. The two chains are held together by non-covalent interactions. The four-step purification includes capture, affinity purification using a monoclonal recombinant antibody, anion exchange chromatography and gel filtration. The specific clotting activity of N8 was 8800-9800 IU mg(-1). Sequence and mass spectrometry analysis revealed two variants of the light chain, corresponding to two alternative N-terminal sequences also known from plasma FVIII. Two variants of the heavy chain are present in the purified product, namely with and without the B-domain linker attached. This linker is removed upon thrombin activation of N8 rendering an activated FVIII (FVIIIa) molecule similar to plasma FVIIIa. All six known tyrosine sulphations of FVIII were confirmed in N8. Two N-linked glycosylations are present in the A3 and C1 domain of the light chain and two in the A1 domain of the heavy chain. The majority of the N-linked glycans are sialylated bi-antennary structures. An O-glycosylation site is present in the B-domain linker region. This site was glycosylated with a doubly sialylated GalNAc-Gal structure in approximately 65% of the product. In conclusion, the present data show that N8 is a pure and well-characterized FVIII product with biochemical properties that equal other FVIII products.

Characterisation of G418-induced metabolic load in recombinant CHO and BHK cells: effect on the activity and expression of central metabolic enzymes.

In a previous article (Yallop and Svendsen 2001), recombinant CHO and BHK cell lines, expressing the human glucagon receptor and the gastric inhibitory peptide receptor, respectively, showed reduced growth rates and altered nutrient utilisation when grown with increasing concentrations of G418. This response was associated with an increased expression of the neo (r) protein, while expression of the recombinant membrane receptors remained unaltered. The metabolic response was characterised in both cell lines by an increase in the specific rate of glutamine utilisation and in CHO cells by a decrease in the yield of lactate from glucose, suggesting a change in the flux of glucose through central metabolism. The aim of this study was to further elucidate these metabolic changes by determining the activity and relative expression of key enzymes involved in glucose and glutamine metabolism. For both CHO and BHK cells, there was an increase in the activity of glutaminase, glutamate dehydrogenase and glutamine synthetase, suggesting an increased flux through the glutaminolysis pathway. The activity of glucose-6-phosphate dehydrogenase and pyruvate carboxylase in CHO cells was also increased whilst lactate dehydrogenase activity remained unaltered, suggesting an increased flux to the pentose phosphate pathway and TCA cycle, respectively. The activity of these enzymes in BHK cells was unchanged. Quantitative RT-PCR showed that expression levels of glutaminase and pyruvate carboxylase were the same with and without G418, indicating that the differences in activities were likely due to post-translational modifications.

Interaction between the transcription factor SPBP and the positive cofactor RNF4. An interplay between protein binding zinc fingers.

The activator of stromelysin 1 gene transcription, SPBP, interacts with the RING finger protein RNF4. Both proteins are ubiquitously expressed and localized in the nucleus. RNF4 facilitates accumulation of specific SPBP-DNA complexes in vitro and acts as a positive cofactor in SPBP-mediated transactivation. SPBP harbors an internal zinc finger of the PHD/LAP type. This domain can form intra-chain protein-protein contacts in SPBP resulting in negative modulation of SPBP-RNF4 interaction.

Human ERRgamma, a third member of the estrogen receptor-related receptor (ERR) subfamily of orphan nuclear receptors: tissue-specific isoforms are expressed during development and in the adult.

The nuclear receptor protein superfamily is a large group of transcription factors involved in many aspects of animal development, tissue differentiation, and homeostasis in the higher eukaryotes. A subfamily of receptors, ERRalpha and beta (estrogen receptor-related receptor alpha and beta), closely related to the ER, were among the first orphan nuclear receptors identified. These receptors can bind DNA as monomers and are thought to activate transcription constitutively, unaffected by beta-estradiol. Studies of the expression patterns of ERRalpha and gene disruption experiments of ERRbeta indicate that they play an important role in the development and differentiation of specific tissues in the mouse. In this work we demonstrate the existence in humans of a third member of this subfamily of receptors, termed ERRgamma, which is highly expressed in a number of diverse fetal and adult tissues including brain, kidney, pancreas, and placenta. The ERRgamma mRNA is highly alternatively spliced at the 5'-end, giving rise to a number of tissue-specific RNA species, some of which code for protein isoforms differing in the N-terminal region. Like ERRalpha and beta, ERRgamma binds as a monomer to an ERRE. A GAL4-ERRgamma fusion protein activates transcription in a ligand-independent manner in transfected HEK293 cells to a greater degree than either the GAL4-ERRalpha or -beta fusion proteins.

Activation of 2'-5' oligoadenylate synthetase by single-stranded and double-stranded RNA aptamers.

A number of small RNA molecules that are high affinity ligands for the 46-kDa form of human 2'-5' oligoadenylate synthetase have been identified by the SELEX method. Surface plasmon resonance analysis indicates that these RNAs bind to the enzyme with dissociation constants in the nanomolar range. Competition experiments indicate that the binding site for the small RNAs on the 2'-5' oligoadenylate synthetase molecule at least partially overlaps that for the synthetic double-stranded RNA, poly(I).poly(C). Several of the RNAs function as potent activators of 2'-5' oligoadenylate synthetase in vitro, although there is no correlation between binding affinity and ability to activate. The RNA aptamers having the strongest activation potential appear to have few base-paired regions. This suggests that 2'-5' oligoadenylate synthetase, which has previously been believed to be activated only by double-stranded RNA, can also be activated by RNA ligands with little secondary structure. Since 2'-5' oligoadenylate synthetase possesses no homology to other known RNA-binding proteins, the development of small specific ligands by SELEX should facilitate studies of RNA-protein interactions and may reveal novel features of the structure-function relationships involving this enzyme.

E-box sequence and context-dependent TAL1/SCL modulation of basic helix-loop-helix protein-mediated transcriptional activation.

TAL1/SCL is a basic helix-loop-helix (bHLH) oncoprotein that is expressed in several cell lines including many hematolymphoid cells, but not in T- and B-lineage cells. The TAL1 gene was originally discovered as being transcriptionally activated by chromosomal rearrangements in T-cell acute lymphoblastic leukemia (T-ALL). Here we have shown that TAL1 and the ubiquitously expressed murine bHLH transcription factor ALF1 formed heterodimers that, compared with ALF1 homodimers, had a more restricted E-box specificity and bound preferentially to the glucocorticoid-responsive E-box (Egre) motif (AACAGATGGT). Overexpression of the dominant inhibitory HLH protein Id1 in NIH3T3 cells reduced the transcriptional activity mediated by ALF1 homodimers, whereas the transcriptional activity mediated by TAL1/ALF1 heterodimers was resistant to Id overexpression. Our results show that ALF1 may serve as a dimerization partner for the bHLH oncoprotein TAL1 and form a complex with a distinctive DNA binding property. These findings support the hypothesis that the leukemic characteristics of the TAL1 oncoprotein could be mediated by activation of a set of target genes as heterodimeric complexes with ubiquitously expressed bHLH transcription factors such as ALF1 and that a principal role of TAL1 might be to neutralize an Id-mediated inactivation.

Various modes of basic helix-loop-helix protein-mediated regulation of murine leukemia virus transcription in lymphoid cell lines.

The transcriptionally regulatory regions of the lymphomagenic Akv and SL3-3 murine leukemia retroviruses (MLVs) contain two types of E-box consensus motifs, CAGATG. One type, EA/S, is located in the upstream promoter region, and the other, E(gre), is located in a tandem repeat with enhancer properties. We have examined the requirements of the individual E-boxes in MLV transcriptional regulation. In lymphoid cell lines only, the E(gre)-binding protein complexes included ALF1 or HEB and E2A basic helix-loop-helix proteins. Ectopic ALF1 and E2A proteins required intact E(gre) motifs for mediating transcriptional activation. ALF1 transactivated transcription of Akv MLV through the two E(gre) motifs equally, whereas E2A protein required the promoter-proximal E(gre) motif. In T- and B-cell lines, the E(gre) motifs were of major importance for Akv MLV transcriptional activity, while the EA/S motif had some effect. In contrast, neither E(gre) nor EA/S motifs contributed pronouncedly to Akv MLV transcription in NIH 3T3 cells lacking DNA-binding ALF1 or HEB and E2A proteins. The Id1 protein was found to repress ALF1 activity in vitro and in vivo. Moreover, ectopic Id1 repressed E(gre)-directed but not EA/S-directed MLV transcription in lymphoid cell lines. In conclusion, E(gre) motifs and interacting basic helix-loop-helix proteins are important determinants for MLV transcriptional activity in lymphocytic cell lines.

E-box variants direct formation of distinct complexes with the basic helix-loop-helix protein ALF1.

The murine transcription factor ALF1 belongs to the class of basic helix-loop-helix proteins specific for the NCAGNTGN-version of the E-box. Binding of homodimeric ALF1 to variants of this motif was studied by a combination of binding site selection technology and DNA modification interference analysis. The results showed that substitutions at the non-conserved positions in the E-box sequence could cause profound alterations in the patterns of specific contacts at the protein-DNA interface. Thus, both the overall extent of the binding region and the backbone phosphate contact pattern differed markedly between closely related E-boxes with similar affinities for ALF1. The identity of the base at the inner N was an important determinant of contact pattern specification. The E-box variants differed in their ability to mediate ALF1 dependent transcriptional activation in vivo. We discuss the possibility that adaptability in basic helix-loop-helix protein-DNA interactions can result in complexes with different functional properties.

Determination of recognition-sequences for DNA-binding proteins by a polymerase chain reaction assisted binding site selection method (BSS) using nitrocellulose immobilized DNA binding protein.

We have developed a simple procedure for rapid determination of a DNA sequence recognized by a DNA binding protein based on immobilization of the protein on nitrocellulose filters. The procedure consists of the following steps: A recombinant protein with a functional DNA binding domain is expressed in E. coli. The protein is purified to homogeneity, immobilized on nitrocellulose paper, and exposed to a pool of double stranded oligonucleotides carrying in the central part a 20 bp random sequence, which is flanked by conserved sequences with restriction endonuclease recognition sites for analytical and subcloning purposes and sequences complementary to polymerase chain reaction primers. Oligonucleotides retained by the DNA-binding protein are liberated by increasing the ionic strength and used in a new binding process after amplification by the polymerase chain reaction technique. Finally the amplified product is cloned for determination of the DNA sequence selected by the DNA-binding protein. Murine Zn-finger and basic helix-loop-helix DNA binding proteins were used to demonstrate the efficiency of the method. We show that the yield of oligonucleotides binding to the protein was increased by several consecutive rounds of filter binding and amplification, and that the protein extracted a specific sequence from the pool of random oligonucleotides.