Three mammalian GGAs (Golgi-localized, gamma-ear-containing, ARF-binding 
proteins), GGA1, 2, and 3 have been implicated in the sorting of mannose 
6-phosphate receptor (MPR). To investigate the distinct roles of GGA2 in 
lysosomal enzyme transport, we established two stable cell lines that had a 
reduced expression of GGA2 by RNA interference. The expression levels of GGA2 
were approximately 5% of the control levels, whereas those of non-targeted GGA1 
and GGA3 were not apparently reduced. The depletion of GGA2 did not cause 
changes in the overall distribution of GGA1, GGA3, cation-dependent MPR, or 
cation-independent MPR. However, the cell lines showed increased secretion of a 
lysosomal enzyme, cathepsin D. In addition, a moderate expression of the 
dominant negative VHS-GAT domain of GGA2 had no effect on the trans-Golgi 
network (TGN) signal of three GGAs, nor was the GGA2 signal affected by the 
expression of VHS-GAT domain of GGA1 or 3. These results suggest that GGA2 is 
recruited to the TGN independently of the other GGAs and is required for the 
efficient sorting of lysosomal enzymes.