Prevalence of the Mercurial-Sensitive EctoATPase in Human Small Cell Lung Carcinoma: Characterization and Partial Purification

Cell surface ATPase (ectoATPase) activity is detected on many mammalian cells. Previous documentation in the rat hepatocyte-hepatoma system indicated that ectoATPase activity increased during tumorigenesis with accompanying changes in enzymatic properties and localization. These results, combined with the recently established characteristics of two distinct ectoATPases, a mercurial-sensitive ectoATPase, and a mercurial-insensitive ectoATPase, suggest that the former is increased, whereas the latter is decreased, during hepatoma formation. We found that the mercurial-sensitive ectoATPase was also expressed at high levels in three lines of human small cell lung carcinoma (SCLC) cells. During purification of this enzyme from an SCLC xenograft, four isoforms of this enzyme, with similar biochemical properties but different ionic charges were detected. The elution of two proteins of 170 and 150 kDa from a DEAE-cellulose column appeared to correlate with elution of ATPase activity. These characterizations should be useful in the further investigation of the molecular structure and function of the SCLC mercurial-sensitive ectoATPase which may be an important cell surface marker of SCLC cells.