IDENTIFICATION OF A HUMAN CDNA-ENCODING A NOVEL PROTEIN-KINASE WITH 2REPEATS OF THE LIM DOUBLE ZINC-FINGER MOTIF

By low-stringency screening of a human hepatoma HepG2 cell cDNA librar y, using the genomic fragment of chick c-sea receptor tyrosine kinase as a probe, we isolated overlapping cDNAs encoding a novel protein kin ase, which we termed LIM-kinase (LIMK). The predicted open reading fra me encodes a 647-amino-acid polypeptide containing a putative protein kinase structure in the C-terminal half. In addition, LIMK has two rep eats of cysteine-rich LIM/double zinc finger motif at the most N-termi nus. To our knowledge, this is the first protein kinase seen to contai n the LIM motif(s) in the molecule. Although the protein kinase domain of LIMK has highly conserved sequence elements of protein kinases, ph ylogenetic analysis revealed that LIMK cannot be classified into any s ubfamily of known protein kinases. Northern blot analysis revealed tha t the single species of LIMK mRNA of 3.3 kb was expressed in various h uman epithelial and hematopoietic cell lines. In rat tissues, LIMK mRN A was expressed in the brain, at the highest level. LIM is suggested t o be involved in protein-protein interactions by binding to another LI M motif. As the LIM domain is frequently present in the homeodomain-co ntaining transcriptional regulators and oncogenic nuclear proteins, LI MK may be involved in developmental or oncogenic processes through int eractions with these LIM-containing proteins.