Using matrix attachment regions to improve recombinant protein production

Chinese hamster ovary (CHO) cells are the system of choice for the production of complex molecules, such as monoclonal antibodies. Despite significant progress in improving the yield from these cells, the process to the selection, identification, and maintenance of high-producing cell lines remains cumbersome, time consuming, and often of uncertain outcome. Matrix attachment regions (MARs) are DNA sequences that help generate and maintain an open chromatin domain that is favourable to transcription and may also facilitate the integration of several copies of the transgene. By incorporating MARs into expression vectors, an increase in the proportion of high-producer cells as well as an increase in protein production are seen, thereby reducing the number of clones to be screened and time to production by as much as 9 months. In this chapter, we describe how MARs can be used to increase transgene expression and provide protocols for the transfection of CHO cells in suspension and detection of high-producing antibody cell clones.

MAR elements regulate the probability of epigenetic switching between active and inactive gene expression

Gene expression often cycles between active and inactive states in eukaryotes, yielding variable or noisy gene expression in the short-term, while slow epigenetic changes may lead to silencing or variegated expression. Understanding how cells control these effects will be of paramount importance to construct biological systems with predictable behaviours. Here we find that a human matrix attachment region (MAR) genetic element controls the stability and heritability of gene expression in cell populations. Mathematical modeling indicated that the MAR controls the probability of long-term transitions between active and inactive expression, thus reducing silencing effects and increasing the reactivation of silent genes. Single-cell short-terms assays revealed persistent expression and reduced expression noise in MAR-driven genes, while stochastic burst of expression occurred without this genetic element. The MAR thus confers a more deterministic behavior to an otherwise stochastic process, providing a means towards more reliable expression of engineered genetic systems.

A new chemical tool (C0036E08) supports the role of adenosine A(2B) receptors in mediating human mast cell activation

Asthma is a chronic inflammatory disease of the airways that involves many cell types, amongst which mast cells are known to be important. Adenosine, a potent bronchoconstricting agent, exerts its ability to modulate adenosine receptors of mast cells thereby potentiating derived mediator release, histamine being one of the first mediators to be released. The heterogeneity of sources of mast cells and the lack of highly potent ligands selective for the different adenosine receptor subtypes have been important hurdles in this area of research. In the present study we describe compound C0036E08, a novel ligand that has high affinity (pK(i) 8.46) for adenosine A(2B) receptors, being 9 times, 1412 times and 3090 times more selective for A(2B) receptors than for A(1), A(2A) and A(3) receptors, respectively. Compound C0036E08 showed antagonist activity at recombinant and native adenosine receptors, and it was able to fully block NECA-induced histamine release in freshly isolated mast cells from human bronchoalveolar fluid. C0036E08 has been shown to be a valuable tool for the identification of adenosine A(2B) receptors as the adenosine receptors responsible for the NECA-induced response in human mast cells. Considering the increasing interest of A(2B) receptors as a therapeutic target in asthma, this chemical tool might provide a base for the development of new anti-asthmatic drugs.

Parallel regulation by olanzapine of the patterns of expression of 5-HT2A and D3 receptors in rat central nervous system and blood cells

Patterns of protein expression can be used to identify biomarkers of disease, prognosis or treatment response. Peripheral 5-HT2A and D3 receptors have been proposed as protein markers in schizophrenia. We investigated the possible parallel regulation of these candidate biomarkers in central nervous system (CNS) and peripheral blood cells by a comparative study of the effects of antipsychotic treatment on the expression of the receptors in both systems in rats. Acute (24 and 48 h) and subchronic (16 days) treatment of rats with olanzapine induced a significant decrease in 5-HT2A receptor density both in frontal cortex (Bmax=76.2%, 83.0% and 46.0% of control after 24 h, 48 h and 16 days of treatment, respectively; P<0.01) and blood platelets (Bmax approximately 55% of control at all times measured; P<0.01), without any changes in receptor affinity. Furthermore, olanzapine induced redistribution in 5-HT2A-like immunoreactivity and time-dependent remodelling of synaptic circuits involved in the activity of pyramidal and GABAergic neurons in frontoparietal motor cortex of treated rats, as assessed by immunohistochemical studies. D3 receptor mRNA levels increased significantly by 52.5% (P<0.01) and 21.1% (P<0.05) in nucleus accumbens, and by 53.4% (P<0.05) and 91.7% (P<0.01) in lymphocytes, after acute (24 h and 48 h) treatment with olanzapine, returning to levels similar to control after subchronic treatment (16 days). In conclusion, we observed in rats after olanzapine treatment: (1) parallelism in the regulation of 5-HT2A receptors in frontal cortex and in blood platelets; (2) parallelism in the regulation of D3 mRNA levels in nucleus accumbens and lymphocytes. These results endorse the interest in future studies aimed at validating these receptors as candidate biomarkers in schizophrenia.

Prothymosin alpha, a mammalian c-myc-regulated acidic nuclear protein, provokes the decondensation of human chromosomes in vitro

Prothymosin (ProT alpha) is an acidic nuclear protein, widely distributed in mammalian cells, whose expression is regulated by c-myc and linked to cell proliferation. ProT alpha interacts with histone H1 via its acidic domain, and its overexpression provokes the unfolding of chromatin fibers. Here we show that incubation of human native metaphase chromosomes with ProT alpha induces their extensive unravelling suggesting a function of this protein in chromosome decondensation.

Overexpression of prothymosin alpha accelerates proliferation and retards differentiation in HL-60 cells

Prothymosin alpha (ProTalpha) is an acidic nuclear protein the expression of which is related to the proliferation and differentiation processes in mammalian cells. In the present study we have stably transfected HL-60 cells, a biological system that allows the study of both proliferation and differentiation, with recombinant vectors encoding sense and antisense ProTalpha mRNA. In the HL-60 cell clones overexpressing ProTalpha we observed an acceleration in the growth rate, whereas expression of the antisense orientation showed the opposite effect. Moreover, cell-cycle analysis demonstrated that the G1-phase was shortened in the cells expressing the sense construct. Before studying how ProTalpha affects differentiation, we showed that the down-regulation of ProTalpha gene during differentiation occurs in all mammalian cell lines (HL-60, K562, U937, MEL C88, N2A and PC12) analysed. The biological effect evoked by the induction of the ProTalpha sense vector was the retardation of cell differentiation, although expression of the antisense construct showed no effect on differentiation. In conclusion, our findings provide evidence that ProTalpha is directly implicated in cellular proliferation and that the maintenance of high levels of ProTalpha inside HL-60 cells is incompatible with their ability to differentiate.

A c-myc antisense oligonucleotide inhibits human retinal pigment epithelial cell proliferation

The purpose of this work was to investigate if MYC-dependent intracellular mitogenic pathway is active in cultures of human retinal pigment epithelial (hRPE) cells and whether myc antisense phosphorotioate oligonucleotides (c-myc-AS-ODN) are useful tools for inhibiting the proliferation of hRPE cells. Cultures of hRPE cells were established from adult human corneal donors. These cells were positively stained for cytokeratins and vimentin. Myc mRNA expression was determined by Northern blot analysis and it was determined by means of immunofluorescence if MYC was expressed. C-myc-AS-ODN effect on cell proliferation was estimated by evaluating the incorporation of 5-bromo-2'-deoxy-uridine into cellular DNA. Cell number was estimated by using a tetrazolium bromide based colorimetric method. Human RPE cells in culture expressed MYC and myc mRNA as well as prothymosin alpha mRNA--a gene whose transcription is under MYC control--indicating that MYC-dependent intracellular mitogenic pathway is active in these cells. In accordance with this, we found that blocking the expression of myc by the addition of c-myc-AS-ODN to the culture medium inhibited hRPE cell proliferation. The effect of the c-myc-AS-ODN was found to be sequence specific (the use of a control oligonucleotide with the same sequence but in an opposite direction had no effect) and dose-dependent (4 microM was the lowest effective dose tested). By using RT-PCR we found that the c-myc-AS-ODN inhibition of cell proliferation was related to a diminution in c-myc mRNA expression, and by immunofluorescence we detected a diminution in c-MYC protein staining in RPE cells after 48 hr of treatment with c-myc-AS-ODN. Furthermore, growth inhibition remained for at least 5 days after addition of a single dose of the c-myc-AS-ODN to the culture. We conclude that hRPE cell proliferation is under MYC control. Blocking the expression of myc by c-myc-AS-ODN inhibited hRPE cell proliferation. These findings establish a rationale for investigating the potential use of a c-myc-AS-ODN as a novel therapeutical tool in the treatment of Proliferative Vitreoretinopathy.

Kidney ATPase response in seawater-transferred rainbow trout (Oncorhynchus mykiss). Effect of salinity and fish size

Two sizes of domesticated rainbow trout (Oncorhynchus mykiss, 40 +/- 0.67 and 180 +/- 3.9 g) were directly transferred to brackish water (9 ppt) and seawater (28 ppt). Kidney Na(+)-K(+)-ATPase and Mg(2+)-ATPase activities were measured in fresh water, and after long-term seawater adaptation (up to 21 days). Renal Na(+)-K(+)-ATPase activity increased after saltwater loading in small trout, while large trout displayed an unmodified ATPase activity. The smallest trout showed a low but progressive increase in renal Mg(2+)-ATPase activity after the transfer to both salinities. However, ATPase activity remained unchanged or significantly decreased in large trout after the transfer to seawater or brackish water, respectively.