Transient transfection induces different intracellular calcium signaling in CHO K1 versus HEK 293 cells

Abstract

For the controlled production of recombinant proteins in mammalian cells by transient transfection, it may be desirable not only to manipulate, but also to diagnose the expression success early. Here, we applied laser scanning confocal microscopy to monitor transfection induced intracellular Ca2+ responses. We compared Chinese hamster ovary (CHO K1) versus human embryo kidney (HEK) 293 cell lines, which differ largely in their transfectability. An improved calcium phosphate transfection method was used for its simplicity and its demonstrated upscale potential. Cytosolic Ca2+ signaling appeared to inversely reflect the cellular transfection fate. Virtually all CHO cells exhibited asynchronous, cytosolic Ca2+ oscillations, which peaked 4 h after addition of the transfecting solution. Yet, most of the HEK cells displayed a slow and continuous Ca2+ increase over the time of transfection. CHO cells, when exposed to a transfection-enhancing glycerol shock, strongly downregulated their Ca2+ response, including its oscillations. When treated with thapsigargin; a Ca2+ store depleting drug, the number of successfully transfected CHO cells was significantly reduced. Our result points to intracellular store release as a critical component for the transfection fate of CHO cells, and its early detection before product visualization.