A VARIANT TRANSCRIPT ENCODING AN ISOFORM OF THE HUMAN PROTEIN-TYROSINE KINASE EPHB2 IS GENERATED BY ALTERNATIVE SPLICING AND ALTERNATIVE USE OF POLYADENYLATION SIGNALS

We previously isolated and characterized cDNA clones of DRT (EPHB2), e ncoding a receptor protein-tyrosine kinase of the EPH family, Northern blot analysis showed that EPHB2 transcripts are expressed in three si zes of approximately 4, 5, and 11 kb, suggesting that these transcript s are generated by alternative splicing and/or alternative use of poly adenylation sites. To explore this possibility, we isolated additional EPHB2 cDNA clones, including clone 5K-1, by re-screening the human fe tal brain cDNA library. Nucleotide sequence analysis of clone 5K-1 rev ealed that it represents a variant transcript of EPHB2 (EPHB2v), Relat ive to the EPHB2 cDNA sequence previously reported, clone 5K-1 has two coding region deletions of 3 and 93 nucleotides. Nucleotide sequence analyses of EPHB2 genomic DNA fragments corresponding to these deletio ns suggest that the EPHB2v transcript is generated by alternative spli cing. The 3' end of clone 5K-1 contains a polyadenosine stretch preced ed by a potential polyadenylation signal, which is not used to generat e the EPHB2 transcript, Taken together, these data indicate that EPHB2 v is generated by both alternative splicing and alternative use of pol yadenylation sites. The EPHB2v protein lacks one arginine residue that resides immediately following the EPHB2 transmembrane domain, In cont rast, as a result of the frame shift caused by the 93 nucleotide delet ion, the C-terminus of the EPHB2v protein is longer by 70 amino acids than that of EPHB2. We also show that the human neuroblastoma cell lin e SY5Y and NTera-2N neurons express high levels of EPHB2 and lower lev els of EPHB2v, These structural variations found between the EPHB2 and EPHB2v proteins may reflect functional heterogeneity of EPHB2.