mRNA is ubiquitously expressed in multiple tissues as a 1.7-kb mRNA; the ubiquitous expression pattern was further confirmed at the protein level (Tomiuk et al., 2000). The over-expressed nSMase1 colocalizes with marker proteins of the endoplasmic reticulum (ER) and the Golgi apparatus by immunocytochemistry (Tomiuk et al., 2000). Although the ER localization was further confirmed (Fensome et al., 2000; Rodrigues-Lima et al., 2000), a subsequent study in hepatoma cells found that endogenous rat nSMase1 localized mainly to the nuclear matrix. This suggests that nSMase1 may function in multiple organelles (Mizutani et al., 2001).
