Novel human oncogene lbc detected by transfection with distinct homology regions to signal transduction products.

In order to isolate transforming genes involved in leukemias, DNA from a CML acute phase sample was transfected into NIH-3T3 cells and found to be tumorigenic in nude mice. Partial genomic cloning using human repeat sequence as probe followed by cDNA cloning of this oncogene, termed lbc, was undertaken. The lbc cDNA sequence shows no identity to known proteins and codes for a predicted hydrophilic protein product of 47 kD, which contains several consensus kinase phosphorylation sites. The N-terminus encodes a consensus E-F hand motif followed by a region of homology to the transforming human oncogene dbl associated with regulatory activity for the ras superfamily of small G proteins, while the C-terminus contains homology with pleckstrin and rac protein kinase in a region which overlaps with the recently defined PH (pleckstrin homology) domain. Lbc expression is restricted to human hematopoietic cells and skeletal muscle, lung and heart. Transfection of 3T3 cells with an expression vector encoding lbc cDNA results in focus formation, demonstrating its biological activity. These data indicate that the lbc oncogene encodes a novel product implicated in distinct cellular signal transduction functions.