Regulated autocrine growth of CHO cells

The goal of this work was to engineer a CHO cell line capable of autocrine growth in a fully defined protein-free medium. This was accomplished by sta ble integration of the genes encoding insulin-like growth factor I (IGF-I) and transferrin into the genome of a CHO-K1 cell line. The lac operator/rep ressor system was used to regulate the expression of the IGF-I gene with th e lac operator sequence being placed upstream of the coding sequence for IG F-I. The expression of the lac repressor protein was driven by a modified m etallothionein promoter allowing repressor expression to be regulated by th e culture medium. The cell line called Super CHOr (r for regulated) was abl e to grow in protein-free medium in an autocrine fashion with a doubling ti me of 20-24 hr, either attached to microcarriers or as aggregate suspension cultures. Upon addition of metal to the culture medium, the repressor prot ein was produced and bound to the operator sequences shutting down the expr ession of IGF-I and arresting the growth of the cells. Expression of the hu man growth hormone (hGH) gene and production of hGH was induced by the pres ence of metal ions. It was possible to release the cells from growth arrest in the presence of metal by the addition of isopropyl beta-D-thiogalactopy ranoside (IPTG), which prevented binding of the repressor to its operator s equences. The ability to grow CHO cells in fully defined protein-free mediu m and to be able to regulate their growth rate offers a number of advantage s for the use of these cells as hosts for the production of recombinant DNA derived proteins.