Abstract
Binding of intergenic Scaffold/Matrix Attachment Regions (S/MARs) to nuclear matrix proteins is believed to poise adjacent genes for transcription by forming chromatin loops. Vector constructs containing Scaffold/Matrix Attachment Regions (S/MAR) flanking the gene of interest, therefore, are able to enhance recombinant protein expression in mammalian cells. We compared two methods that are based on buffers containing 2M NaCl and Lithium-3,5-diidosalicylate (LIS) to isolate S/MARs from HEK293 and CHO DG44 cell lines. Isolated S/MARs were sequenced using the Illumina HiSeq platform and mapped against CHO DG44 genome contigs and the human genome GRCh37.p13 respectively (Sequence raw data from this article have been deposited at the EMBL Data Libraries under Study ID PRJEB26090 (ERP108063)). The 2M NaCl method produced 16 million S/MAR consensus sequences which included nine million and seven million from HEK293 and CHO DG44 respectively. LIS method, on the other hand, generated thirteen million S/MAR consensus containing 8.4 million and 4.7 million from HEK293 and CHO DG44, respectively. In order to compare all sets of S/MAR consensus, BLASTN analyses were performed based on exact matches. The number of perfect matches between S/MAR sequences produced by both methods was quite low: 0.46% and 0.07% for HEK293 and CHO DG44 cells respectively, indicating that the two methods isolate different sets of S/MARs. Comparison between the two cell lines found six S/MARs in common, with average coverage of 82%, obtained by the 2M NaCl method, but none of these are intergenic. The LIS method gave 38 S/MARs with average coverage of 85%, common to both cell types; of these, 13 were intergenic. We hypothesize that S/MARs from HEK293 and CHO DG44 isolated using the LIS method have the potential to be universal vector expression elements that can overcome the problem of low production yield.
Highlights
In the era of modern medicine, recombinant protein therapeutics are contributing significantly to innovative and effective therapies for treatment of numerous human diseases (Agarwal et al, 1998)
While the information for a genome-wide study has not been established for mammalian cells, our study aims to identify Scaffold/Matrix Attachment Regions (S/Matrix Attachment Region (MAR)) sequences based on both LIS (Keaton et al, 2011) and NaCl (Krawetz et al, 2005) extraction methods for two different mammalian cell lines, CHO DG44 and HEK 293, at genome level using the Solexa sequencing platform (Illumina Incorporation, USA)
The percentages of DNA recovered in the S/MAR and loop fractions were determined in order to evaluate the distribution of both fractions after being isolated by these two methods (Table 1)
Summary
In the era of modern medicine, recombinant protein therapeutics are contributing significantly to innovative and effective therapies for treatment of numerous human diseases (Agarwal et al, 1998). Therapeutic proteins such as antibodies and enzymes, produced in mammalian cells, have been successfully utilized in the treatment of diseases in the past decade. The positional effect of transgene integration sites might hinder the effectiveness of the recombinant protein expression in the transfected cells This factor could be due to the influences of the chromatin structure effects and/or dominant regulatory elements flanking the integration sides of the gene (Feng et al, 2001).
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