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Selection of host cells expressing protein at high levels

a high-level protein and host cell technology, applied in the field of molecular biology and biotechnology, to achieve the effect of rapid and efficient creation of stable mammalian cell lines and increased probability of high expression

Inactive Publication Date: 2011-12-08
CHROMAGENICS BV
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

"The patent text describes a method for selecting host cells that produce high levels of a polypeptide of interest using a multicistronic transcription unit. The method involves using a selectable marker polypeptide that is translationally impaired by mutations. The mutations in the selectable marker polypeptide are made to impair its translation initiation. The patent also describes a DNA molecule that includes a translation start sequence for the selectable marker polypeptide. The DNA molecule can be used to select host cells with high levels of expression of the polypeptide. The invention provides further advantageous embodiments and improvements to the methods and DNA molecule described in the incorporated patents."

Problems solved by technology

One problem associated with the expression of transgenes is that it is unpredictable, stemming from the high likelihood that the transgene will become inactive due to gene silencing (McBurney et al., 2002), and therefore many host cell clones have to be tested for high expression of the transgene.

Method used

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  • Selection of host cells expressing protein at high levels
  • Selection of host cells expressing protein at high levels
  • Selection of host cells expressing protein at high levels

Examples

Experimental program
Comparison scheme
Effect test

example 1

Construction and Testing of a Zeocin-Resistance Gene Product with No Internal Methionine

[0198]The basic idea behind the development of the novel selection system of the incorporated '525 application is to place the gene encoding the resistance gene upstream of a gene of interest, and one promoter drives the expression of this bicistronic mRNA. The translation of the bicistronic mRNA is such that only in a small percentage of translation events the resistance gene will be translated into protein and that most of the time the downstream gene of interest will be translated into protein. Hence the translation efficiency of the upstream resistance gene is severely hampered in comparison to the translation efficiency of the downstream gene of interest. To achieve this, three steps can be taken according to the invention of the '525 application:[0199]1) within the resistance gene on the mRNA, the searching ribosome preferably should not meet another AUG, since any downstream AUG may serve ...

example 2

Creation and testing of Zeocin-d2EGFP Bicistronic Constructs with Differential Translation Efficiencies

[0208]To create a bicistronic mRNA encompassing a mutated Zeocin-resistance mRNA with less translational efficiency, and the d2EGFP gene as downstream gene of interest, the start codon of the d2EGFP gene was first optimized (step 3 in Example 1). After that, the different versions of the Zeocin-resistance gene were created. The differences between these versions are that they have different start codons, with distinct translational efficiency (step 2 in Example 1, FIG. 1C-E). These different ZEOCIN®-resistance gene versions were cloned upstream of the modified d2EGFP gene (FIG. 2).

Materials and Methods

Creation of Plasmids

[0209]The d2EGFP reporter ORF was introduced into pcDNA3. The sequence around the start codon of this d2EGFP cDNA is GAATTCGG (start codon in bold; SEQ ID NO:73), which is not optimal. As a first step, d2EGFP was amplified from pd2EGFP (Clontech 6010-1) with primer...

example 3

Establishment of a Higher Number of TTG Zeo STAR Colonies and Comparison with an IRES-Zeo Construct

[0218]The results in example 2 indicate that the TTG Zeo has extremely stringent translation efficiency, which might be to high to convey ZEOCIN® resistance to the cells. The transfection was scaled up to test whether there would be some colonies that have such high expression levels that they survive. Scaling up the experiment could also address the question whether the high average of TTG Zeo STAR 7 / 67 / 7 would become higher when more colonies were analyzed.

Materials and Methods

[0219]CHO-K1 cells were transfected with the constructs that have the TTG Zeo gene as selection marker, with and without STAR elements 7 and 67 (FIG. 4). Transfections, selection, culturing etc were as in example 2, except that 6 times more cells, DNA and Lipofectamine 2000 were used. Transfections and selection were done in Petri dishes.

Results

[0220]FIG. 4A shows that transfection with the TTG Zeo STAR 7 / 67 / 7 ...

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Abstract

Described is a DNA molecule comprising an open reading frame sequence that encodes a selectable marker polypeptide, wherein the DNA molecule in the coding strand comprises a translation start sequence for the selectable marker polypeptide having a GTG start codon or a TTG start codon, and wherein the ORF sequence that encodes the selectable marker protein has been mutated to replace at least half of its CpG dinucleotides as compared to the native ORF sequence that encodes the selectable marker protein. Further provided are such DNA molecules wherein the ORF sequence that encodes a selectable marker polypeptide is part of a multicistronic transcription unit that further comprises an open reading frame sequence encoding a polypeptide of interest. Also described are methods for obtaining host cells expressing a polypeptide of interest, wherein the host cells comprise the DNA molecules described herein. Further provided is the production of polypeptides of interest, comprising culturing host cells comprising the DNA molecules described herein.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a continuation of co-pending U.S. patent application Ser. No. 11 / 416,490, filed May 2, 2006, which is a continuation-in-part of co-pending U.S. patent application Ser. No. 11 / 269,525, filed Nov. 7, 2005, which application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application Ser. No. 60 / 626,301, filed Nov. 8, 2004, and U.S. Provisional Patent Application Ser. No. 60 / 696,610, filed Jul. 5, 2005. U.S. patent application Ser. No. 11 / 269,525 also claims the benefit of EP 04105593.0, filed Nov. 8, 2004. This application is further a continuation-in-part of co-pending U.S. patent application Ser. No. 11 / 359,953, filed Feb. 21, 2006, and which itself is a continuation-in-part of the aforementioned co-pending U.S. patent application Ser. No. 11 / 269,525, filed Nov. 7, 2005. This application is also a continuation of co-pending U.S. Ser. No. 12 / 226,706, filed Oct. 24, 2008, which is the national stage...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C12P21/02C12N15/85C12N15/63C12N1/00C12N1/21C07H21/04C12N5/10
CPCC12N15/67C12N15/85C12N2840/206C12N2840/20C12N2830/46C12N9/1205C12N2840/203C12N2840/50C12Y207/01095C07K14/505
Inventor OTTE, ARIE PIETERVAN BLOKLAND, HENRICUS JOHANNES MARIAKWAKS, THEODORUS HENDRIKUS JACOBUSSEWALT, RICHARD GEORGE ANTONIUS BERNARDUS
Owner CHROMAGENICS BV
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