SLC9A1 and breast carcinoma: Furthermore, MDA-MB-231 breast cancer cells expressing this CR variant (1K3R4E) showed increased invasion, migration, and spheroid growth compared to cells expressing WT NHE1 (Amith et al., 2016). The other two NHE1 variants expressed were S648A and S648D, representing the non-phosphorylated and phosphorylated states of S648, respectively.