Determining subcellular localization of novel drug targets by transient transfection in COS cells

Genomics-based approaches are increasingly being used to identify disease-associated genes that represent potential new drug targets. As a first step in the validation of genes of unknown function, we describe a method for rapidly determining the subcellular localization of the gene product. If an immunotherapeutic approach is being considered, it is of particular interest to identify targets that are either on the cell-surface or secreted. Transient expression in COS cells combined with immunofluorescent staining provides a semi-high throughput method for determining the subcellular localization of multiple targets in parallel. COS cells are ideal for this purpose since: (i) they transfect easily; (ii) the high levels of expression that can be achieved transiently allow detection after 24 h; and (iii) the relatively large size and spread morphology of these cells allows the subcellular organelles to be easily visualized. To evaluate the system, we show prototype staining patterns for known cytoplasmic, secreted, Golgi-associated, endoplasmic reticulum-associated, and plasma membrane proteins, as well as data for novel targets. The localization of novel secretory and cell-surface proteins as determined by immunofluorescent staining, was confirmed by independent methods.