Many biomedically significant proteins, including antibodies, cytokines, anticoagulants, blood clotting factors, and others are glycoproteins. Thus, there is a high demand for systems that can be used to produce recombinant glycoproteins for basic biomedical research and direct clinical applications. However, currently available recombinant protein production systems cannot meet this demand. In fact, no currently available system can produce large amounts of recombinant glycoproteins in properly glycosylated form at relatively low cost. The long-term objective of this proposal is to genetically engineer the silkworm to fulfill these requirements and provide a new system for recombinant glycoprotein production. Recent studies have shown that the silkworm silk gland, which is a highly efficient silk protein production and secretion organ, can be genetically engineered to efficiently produce and secrete recombinant proteins. But, transgenic silkworms have been neither developed nor used for recombinant glycoprotein production. The major impediment is that the endogenous protein glycosylation pathways of the silk gland cannot be expected to properly glycosylate higher eukaryotic glycoproteins. We will use metabolic engineering to overcome this impediment, as part of a broader effort to develop the silkworm as a new system for recombinant human glycoprotein production. The basic approach will be to use the piggyBac vector system to isolate transgenic silkworms encoding (1) higher eukaryotic enzymes needed to humanize the native silk gland protein N-glycosylation pathway and (2) a recombinant human N-glycoprotein. Each transgene will be placed under the control of a tissue-specific promoter that will target its expression to the silk gland. There are no previous reports of recombinant glycoprotein production using any type of transgenic insect as a bioreactor. In addition, there are no previous reports of engineering a protein glycosylation pathway in any multicellular animal. Therefore, the proposal to use the silk gland of a transgenic silkworm as a bioreactor for recombinant glycoprotein production and secretion, coupled with the proposal to metabolically engineer the protein N-glycosylation pathway in a major organ of this lower eukaryote, is truly original and innovative. The specific aims of this proposal are (1) To construct and test piggyBac vectors for silk gland-specific expression of genes encoding (1a) enzymes needed to humanize the silkworm protein N-glycosylation pathway and (1b) genes encoding a recombinant human glycoprotein of interest;(2) To use the piggyBac vectors from aim 1 to produce transgenic silkworms;and (3) To assess recombinant glycoprotein production, secretion, and glycosylation by the transgenic silkworms from aim 2.The glycoproteins are a major subclass of proteins distinguished by the presence of carbohydrate side chains covalently linked to the polypeptide backbone. Many different types of biomedically significant proteins, such as antibodies, cytokines, anticoagulants, blood clotting factors are glycoproteins. Modern biomedical researchers studying human glycoproteins or producing them for clinical use rely heavily on recombinant protein production systems. Thus, there is a high demand for systems that can be used to produce recombinant glycoproteins. Unfortunately, few of the currently available systems are well suited for the production of recombinant glycoproteins, as few can produce higher eukaryotic glycoproteins with authentic carbohydrate side chains. Thus, the basic purpose of the research proposed herein is to create a new system that can be used to produce recombinant glycoproteins for basic biomedical research and direct clinical applications. More specifically, we will genetically engineer the silkworm to create this new system. While it might seem strange to target a caterpillar, such as the silkworm, to develop a recombinant glycoprotein production system, we have good reasons to do so. One major reason is that the silkworm silk gland has evolved over millions of years as a highly efficient protein production and secretion organ. Furthermore, several published studies have shown that this organ can be engineered to efficiently produce and secrete recombinant proteins. However, silkworms have not been used for recombinant glycoprotein production because their endogenous protein glycosylation pathways cannot properly glycosylate foreign, higher eukaryotic glycoproteins. Together, the Jarvis and Fraser labs are uniquely positioned to address this problem. The Jarvis lab has been studying and engineering insect protein glycosylation pathways for the past decade and the Fraser lab has developed a superb system for efficient genetic transformation of insects, particularly the silkworm. Thus, we plan to combine our skills to isolate transgenic silkworms that will encode both the higher eukaryotic enzymes needed to humanize their protein glycosylation pathway and a biomedically relevant human glycoprotein of interest. Importantly, the expression of each transgene will be specifically targeted to the silk gland placed using a tissue-specific promoter. There are no previous reports of recombinant glycoprotein production using any type of transgenic insect as a bioreactor. There also are no previous reports of engineering a protein glycosylation pathway in any multicellular animal. Therefore, our proposal to use the silk gland of a transgenic silkworm as a bioreactor for recombinant glycoprotein production and secretion, coupled with our proposal to metabolically engineer the protein N-glycosylation pathway in a major organ of this lower eukaryote, is truly original and innovative. The successful development of the silkworm as a system for recombinant glycoprotein production would have a broad impact with implications in many areas of biomedical research. A better tool for recombinant glycoprotein production would facilitate basic research on glycoprotein structure and function. It also could be used in the biotechnology industry to produce recombinant glycoproteins for clinical use as vaccines or therapeutics. Again, while it might seem like a strange platform, the idea to use caterpillars for the production of non-glycosylated proteins has already been commercialized (see www.c-perl.com). The biotechnological impact of this system could be huge, considering that many high profile, clinically relevant proteins, such as antibodies (e.g. herceptin.), cytokines (e.g. EPOGEN), and anticoagulants (e.g. Tenecteplase") are glycoproteins. At a more basic level, the metabolic engineering effort, which is key to this project, represents an elaborate ectopic expression experiment that will broadly address the biological significance of the differences in protein N-glycosylation pathways of lower and higher eukaryotes. These results will be of great interest to basic scientists, particularly glycobiologists studying protein N-glycosylation in lower organisms and the evolution of protein glycosylation pathways. Finally, these results will be of great interest to bioengineers working to overcome the evolutionary limitations of lower eukaryotic systems for recombinant glycoprotein production.
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