Advances Made Toward Bioengineering Heparin in Cultured Cells

Researchers at the University of California San Diego report that they are one step closer to the ability to make heparin in cultured cells. Heparin, a potent anti-coagulant, is the most prescribed drug in hospitals yet cell-culture-based production of heparin is currently not possible. Heparin is currently produced by extracting the drug from pig intestines. Ten years ago, contaminants from the pig preparations led to dozens of deaths.

According to a paper published in PNAS last week, the team found a critical gene in heparin biosynthesis: ZNF263 (zinc-finger protein 263). The researchers believe this gene regulator is a key discovery on the way to industrial heparin production. The idea would be to control this regulator in industrial cell lines using genetic engineering, paving the way for safe industrial production of heparin in well-controlled cell culture.

The UC San Diego team used bioinformatic software to scan the genes encoding enzymes involved in heparin production, specifically looking for sequence elements that could represent binding sites for transcription factors. The existence of such a binding site could indicate that the respective gene is regulated by a corresponding gene regulator protein, i.e. a transcription factor.

"One DNA sequence that stood out the most is preferred by a transcription factor called ZNF263 (zinc-finger protein 263)," explains co-author Nathan E. Lewis. "While some research has been done on this gene regulator, this is the first major regulator involved in heparin synthesis, he added.

Using CRISPR/Cas9, the researchers mutated ZNF263 in a human cell line that normally does not produce heparin. They found that the heparan sulfate that this cell line would normally produce was now chemically altered and showed a reactivity that was closer to heparin. Experiments further showed that ZNF263 represses key genes involved in heparin production. Interestingly, analysis of gene expression data from human white blood cells showed suppression of ZNF263 in mast cells and basophils, which are related to mast cells. The researchers report that ZNF263 appears to be an active repressor of heparin biosynthesis throughout most cell types, and mast cells are enabled to produce heparin because ZNF263 is suppressed in these cells.

This finding could have important relevance in biotechnology. Cell lines used in industry (such as CHO cells that normally are unable to produce heparin) could be genetically modified to inactivate ZNF263 which could enable them to produce heparin, like mast cells do.