Expression of PMCA-type Ca2+ pumps in gastric and colon cancer cell lines. Equal amounts (30 μg/lane) of total cellular proteins from various gastric (KATO-III) and colon (DLD-1, Caco-2, LS-174T and HT-29) cancer cell lines were loaded for SDS-PAGE, electroblotted and immunostained for: overall PMCA expression using the 5F10 (upper panel); PMCA4b expression using the JA3 (middle panel) and for PMCA4 (4a and 4b) expression using the JA9 (lower panel) monoclonal antibodies. 5 μg of microsomal membrane protein from the epithelial HeLa cells was mixed with 25 ng of microsomal membrane protein from COS-7 cells transfected with the PMCA4a cDNA. This mixed sample was loaded onto the gel to mark the position of the PMCA1b, 4a and 4b isoforms within a single sample.
PMCA1b is the major PMCA isoform in the gastric/colon cancer cell lines. The expression of PMCA4b, but not that of the PMCA4a protein could also be detected in these cells at a lower level.