Enhanced expression of a 37,000-dalton protein in human lung cancers

When proteins in the tissue extracts of lung cancers were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (PAGE), a 37,000-dalton protein (37K) was detected as a prominent form in all cases thus far examined. This protein was barely detectable or its amount was very small in the normal lung tissue extracts. Two-dimensional PAGE of lung tumor extracts showed 37K as a major spot with an isoelectric point of 7.6. An antibody against 37K was raised in a rabbit by injecting purified 37K. Immunoblot analysis of normal lung and lung tumor tissues revealed that the affinity-purified anti-37K antibody specifically recognized 37K and that the intensities of immunostaining corresponded to those of Coomassie brilliant blue staining.