Activation of a Tumor-associated Protein Kinase (p40^TAK) and Casein Kinase 2 in Human Squamous Cell Carcinomas and Adenocarcinomas of the Lung

Abstract

Several non-small cell lung carcinomas (squamous cell carcinomas and adenocarcinomas) were analyzed for protein kinase activity. Soluble protein extracts derived from these tumors and from the lung parenchyma adjacent to the tumors were resolved by Mono Q anion exchange chromatography, and the fractions were assayed for phosphotransferase activity towards in vitro substrates. Myelin basic protein, casein, and a ribosomal S6-1 COOH-terminus peptide were efficient substrates for protein kinases that exhibited elevated phosphotransferase activity in the tumor extracts when compared to extracts derived from the adjacent nonneoplastic lung or from the lung parenchyma from patients with nonneoplastic lung disorders. Casein phosphotransferase activity was resolved into two peaks that eluted at 0.44 m NaCl and 0.56 m NaCl. The second peak was identified as casein kinase 2, based upon immunoreactivity to casein kinase 2-specific antipeptide antibodies and its sensitivity to inhibition by heparin sulfate. Myelin basic protein phosphotransferase activity eluted at 0.44 m NaCl, but Western blot analysis revealed that this could not be ascribed to mitogen-activated protein (MAP) kinases. This tumor associated protein kinase, designated p40^TAK, exhibited a molecular mass of approximately 40 kDa upon gel filtration. In addition to myelin basic protein, it phosphorylated S6 peptide analogues and histone H1 on seryl residues. Like casein kinase 2, p40^TAK exhibited elevated basal phosphotransferase activity in squamous cell carcinomas and adenocarcinomas of the lung when compared to the nonneoplastic lung parenchyma adjacent to the tumor.