N-Acetylglucosaminyltransferase III Expression in Lower Eukaryotes

Abstract

The present invention relates to eukaryotic host cells having modified oligosaccharides which may be modified further by heterologous expression of a set of glycosyltransferases, sugar transporters and mannosidases to become host-strains for the production of mammalian, e.g., human therapeutic glycoproteins. The process provides an engineered host cell which can be used to express and target any desirable gene(s) involved in glycosylation. Host cells with modified lipid-linked oligosaccharides are created or selected. N-glycans made in the engineered host cells exhibit GnTIII activity, which produce bisected N-glycan structures and may be modified further by heterologous expression of one or more enzymes, e.g., glycosyltransferases, sugar transporters and mannosidases, to yield human-like glycoproteins. For the production of therapeutic proteins, this method may be adapted to engineer cell lines in which any desired glycosylation structure may be obtained.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a continuation of U.S. application Ser. No. 10 / 680,963, which is a continuation-in-part of U.S. application Ser. No. 10 / 371,877, filed on Feb. 20, 2003, now U.S. Pat. No. 7,449,308, which is a continuation-in-part of U.S. application Ser. No. 09 / 892,591, filed Jun. 27, 2001, now U.S. Pat. No. 7,029,872, which claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 60 / 214,358, filed Jun. 28, 2000, U.S. Provisional Application No. 60 / 215,638, filed Jun. 30, 2000, and U.S. Provisional Application No. 60 / 279,997, filed Mar. 30, 2001, each of which is incorporated herein by reference in its entirety. This application is also a continuation-in-part of PCT / US02 / 41510, filed on Dec. 24, 2002, which claims the benefit of U.S. Provisional Application No. 60 / 344,169, filed on Dec. 27, 2001, each of which is incorporated herein by reference in its entirety.REFERENCE TO SEQUENCE LISTING SUBMITTED ELECTRONICAL...

AI Technical Summary

Benefits of technology

[0034]The present invention thus provides a glycoprotein production method using (1) a lower eukaryotic host such as a unicellular or filamentous fungus, or (2) any non-human eukaryotic organism that has a different glycosylation pattern from humans, to modify the glycosylation composition and structures of the proteins made in a host organism (“host cell”) so that they resemble more closely carbohydrate structures found in mammalian, e.g., human proteins. The process allows one to obtain an engineered host cell which can be used to express and target any desirable gene(s), e.g., one involved in glycosylation, by methods that are well-established in the scientific literature and generally known to the artisan in the field of protein expression. Host cells with modified oligosaccharides are created or selected. For the production of therapeutic proteins, this method may be adapted to engineer cell lines in which any desired glycosylation structure may be obtained.

Problems solved by technology

Improper localization of a glycosylation enzyme may prevent proper functioning of the enzyme in the pathway.

Alternatively, the host organism may not provide an adequate level of UDP-GlcNAc in the Golgi or the enzyme may be properly localized but nevertheless inactive in its new environment.

The mere presence of Man5GlcNAc2, therefore, does not assure that further in vivo processing of Man5GlcNAc2 can be achieved.

To date, there is no reliable way of predicting whether a particular heterologously expressed glycosyltransferase or mannosidase in a lower eukaryote will be (1), sufficiently translated (2), catalytically active or (3) located to the proper organelle within the secretory pathway.

Inherent problems associated with all mammalian expression systems have not been solved.

Therapeutic glycoproteins produced in a microorganism host such as yeast utilizing the endogenous host glycosylation pathway differ structurally from those produced in mammalian cells and typically show greatly reduced therapeutic efficacy.

However, N-glycans resembling those made in human cells were not obtained.

However, Man8GlcNAc2 is not a substrate for mammalian glycosyltransferases, such as human UDP-GlcNAc transferase I, and accordingly, the use of that mutant strain, in itself, is not useful for producing mammalian-like proteins, i.e., those with complex or hybrid glycosylation patterns.

While this structure has utility, the method has the disadvantage that numerous enzymatic steps must be performed in vitro, which is costly and time-consuming.

Isolated enzymes are expensive to prepare and need costly substrates (e.g., UDP-GlcNAc).

The method also does not allow for the production of complex glycans on a desired protein.

However, to date, no reports exist that show the high level in vivo trimming of Man8GlcNAc2 to Man5GlcNAc2 on a secreted glycoprotein from P. pastoris.

Moreover, the mere presence of an α-1,2-mannosidase in the cell does not, by itself, ensure proper intracellular trimming of Man8GlcNAc2 to Man5GlcNAc2.

Accordingly, mere localization of a mannosidase in the ER or Golgi is insufficient to ensure activity of the respective enzyme in that targeted organelle.

Re-engineering glycoforms of immunoglobulins expressed by mammalian cells is a tedious and cumbersome task.

Such a growth-inhibition effect complicates the ability to coexpress the target protein and GnTIII and may impose an upper limit on GnTIII overexpression.

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