FIGURE 4.

SALM4 trans-cellular interactions are mediated by its extracellular domain. A, HeLa cells were transiently transfected with SALM2 and SALM4 chimeras tagged with HA or Myc at their N termini. Total staining was detected with antibodies to the C termini of SALM2 and SALM4. Exchanging the extracellular domain of SALM2 with the N terminus of SALM4 induces the clustering of the SALM2 C-terminal region (inset). However, replacing the extracellular domain of SALM4 with the N terminus of SALM2 prevents the clustering seen with SALM4, suggesting that clustering is mediated by the SALM4 extracellular domain. B, HeLa cells transiently transfected with SALM4 were incubated in calcium-free media for 20 h (left panel) or treated with 0.1 mm EGTA for 30 min (right panel). In the absence of calcium, SALM4 expressing cells still form clusters between cells, suggesting that SALM4 trans-cellular interactions are not mediated by a calcium-dependent mechanism.