Abstract
In this report we describe the identification and characterization of a novel tumor-associated receptor-type tyrosine kinase (hek). We produced a monoclonal antibody (III.A4) that detected a novel glycoprotein on the immunizing pre-B cell acute lymphoblastic leukemia cell line (LK63). This antigen was shown to be expressed sporadically on hemopoietic tumor cell lines and on ex vivo tumors. However, using antibody staining, the molecule was undetectable on normal tissues. Further biochemical characterization showed this molecule (hek) to be a phosphoroprotein. This observation taken together with the tumor-associated nature of hek expression suggested that hek might be a receptor-type protein tyrosine kinase. This was demonstrated by affinity purification of hek. In in vitro kinase experiments the purified hek protein was autophosphorylated on tyrosine and also mediated tyrosine phosphorylation of casein. Purified hek was subjected to N-terminal amino acid sequence analysis which showed that hek had a unique N terminus. Amino acid sequence determination of peptides from a V8 protease digest of hek yielded one 21-amino acid stretch of sequence which showed close homology with the eph subfamily of protein tyrosine kinases. These studies show hek to be a novel human tumor-associated protein tyrosine kinase, which by analogy with previously characterized protein tyrosine kinase proto-oncogenes, may have a role in tumorigenesis.
Highlights
From the $Lions Clinical Cancer Research Laboratory and the )IJoint Protein Sequence Laboratory,the Walter and Eliza Hall
Purifiedhek was subjected to N-terminal amino acid sequence analysis which showed that hek had a unique N terminus
Amino acid sequence determination of peptides from a VS protease digest of hek yielded one 21-amino acid stretch of sequence which showed close homologywith the eph subfamily of prokinases which, after myristylation, become associated with the inner leaf of the cell membrane (18).Within the hemopoietic system a number of lineage-restricted src-like kinases have been defined (19).For example the T cell-associated srclike kinase, Ick, has been shown to associate independently tein tyrosine kinases
Summary
Further biochemical characterization showtehdis mol- kinase proteins ingrowth control came from the study of viral ecule (hek)to be a phosphoroprotein.This observation oncogenes (16, 17) These genes were shown to be directly taken togetherwith the tumor-associated natuorfehek involved in growth dysregulation by the introduction of DNA expression suggested thahtek might be a receptor-typeencoding these genes into murine fibroblasts. Amino acid sequence determination of peptides from a VS protease digest of hek yielded one 21-amino acid stretch of sequence which showed close homologywith the eph subfamily of prokinases which, after myristylation, become associated with the inner leaf of the cell membrane (18).Within the hemopoietic system a number of lineage-restricted src-like kinases have been defined (19).For example the T cell-associated srclike kinase, Ick, has been shown to associate independently tein tyrosine kinases These studies show hek to be a with both the CD4 and CD8 transmembrane glycoproteins to novel human tumor-associated proteintyrosine kinase, form a signaling complex (20, 21). We assigned this molecule the provisional name hek (human ephlelk-like kinase).The possible role of hek in the neoplastic process is discussed
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
