The "SWITCH" Project

The Problem

Producing complex therapeutic proteins requires biosynthesis in mammalian cells. The produced proteins can sometimes have some level of toxicity for the cells, limiting the productivity if they are produced constantly and accumulating. Additionally, in a bioreactor setup, the synthesis of a particular protein is usually activated upon addition of a particular molecule. Additional molecules are rarely easily removable.

The pharmaceutical industry needs an easier way to induce the production of a particular compound in mammalian cells.

And this is where our "SWITCH" project steps in.

The First Switch

We want to transfect a light switch along with the gene of interest. This means that the product will only be synthesized by the cells in the presence of blue light, allowing them to grow happily in the dark. The switch is based in an already existing chimeric protein, LovTAP. This protein was originally intended to act as a light-induced repressor in bacteria. The EPFL 2009 iGEM team proposed to fuse it with VP16, a viral activator, in order to convert it into a light-induced activator in mammalian cells. This year we will try to realize this idea by transfecting CHO (Chinese hamster ovary) cells with two plasmids: one coding for the LovTAP-VP16 fusion protein and another with a read-out protein preceded by a binding site for LovTAP-VP16. If everything goes as expected, LovTAP-VP16 will only bind the plasmid and activate the production of read-out when exposed to light.

The Other Switch

In addition, we will be realizing the light switch described by Fussenegger et al. In this light switch, light-sensitive melanopsin triggers a cascade involving calcium ion channels that eventually leads to the transcription of the gene of interest. Fussenegger's team did this using HEK (human embryo kidney) cells, and we will also try to make it work on CHO cells.