Molecular cloning and characterization of TPP36 and its isoform TPP32, novel substrates of Abl tyrosine kinase

We have molecularly cloned TPP36, a novel 36 kDa protein with 281 amino acids that was identified as a protein phosphorylated in B progenitor cells following stimulation with pervanadate/H2O2. Analysis with anti-TPP36 antiserum revealed that TPP36 was expressed ubiquitously and had an isoform with 236 amino acids, designated TPP32. TPP36/32 were localized mainly in cytoplasm despite the presence of a typical nuclear localization signal sequence. These proteins were phosphorylated preferentially by Abl among a panel of tyrosine kinases examined. Phosphorylation of tyrosine 120 in TPP36/32 led to an apparent mobility shift in sodium dodecyl sulfate–polyacrylamide gel electrophoresis, suggesting conformational change in the phosphorylated protein. Thus, TPP36/32 appear to be novel substrates of Abl tyrosine kinase.