Sarco/endoplasmic reticulum Ca2+ ATPases (SERCAs) PUMP free Ca2+ from the cytosol into the endoplasmic reticulum. The human SERCA3 family counts six members named SERCA3a to 3f. However, the exact role of these different isoforms in cellular physiology remains undetermined. In this study, we compared some physiological consequences of SERCA3b and SERCA3f overexpression in HEK-293 cells. We observed that overexpression of SERCA3b, affected cell adhesion capacity associated with a major disorganization of F-actin and a decrease in focal adhesion. Furthermore, we found that SERCA3f overexpression resulted in an increase in endoplasmic reticulum stress markers (including processing of X-box-binding protein-1 (XBP-1) mRNA and expression of chaperone glucose-regulated protein 78 (GRP78)). This was associated with the activation of caspase cascade and a higher spontaneous cell death. In conclusion, these data point for the first time to distinct physiological roles of SERCA3 isoforms in cell functions. (c) 2006 Elsevier Inc. All rights reserved.