Identification of a novel type of alternative splicing of a tyrosine kinase receptor. Juxtamembrane deletion of the c-met protein kinase C serine phosphorylation regulatory site.

We have detected a novel type of structural variant of the tyrosine kinase receptor for c-met, also known as the hepatocyte growth factor receptor, in mouse tissues. The cDNA of the variant transcript of c-met lacks 141 base pairs, which predicts an in-frame deletion of 47 amino acids in the juxtamembrane region of the cytoplasmic domain. Sequence analysis of genomic DNA containing the c-met locus revealed that the absence of a discrete exon is responsible for this 141-base pair deletion and that alternative splicing leads to production of two forms of transcript. These two forms of transcript are designated as c-metsm (for small) and c-metlg (for large) to distinguish the absence or presence of the 141-base pair segment, respectively. The c-metsm variant is present in adult mouse tissues including kidney, liver, and brain as well as in 9-10-day-old embryos. In all cases, expression of c-metsm was lower than that of the normal transcript, c-metlg. An antiserum against mouse c-Met protein immunoprecipitated corresponding protein forms of approximately 152 and approximately 145 kDa from whole kidney lysate under reducing conditions. The size difference of approximately 7 kDa between these isoforms corresponds to the predicted difference of 47 amino acids. The presence of this shorter variant transcript and its corresponding protein isoform in a variety of normal tissues suggests a physiological role. The deleted region in the cytoplasmic domain of c-metsm contains a sequence motif (S985ARS) for protein kinase C phosphorylation that has recently been shown to play a key role in the down-regulation of hepatocyte growth factor receptor kinase activity. The identification of this novel isoform, c-metsm, demonstrates that a tyrosine kinase receptor can achieve additional diversity by alternative splicing at a key regulatory site in its cytoplasmic domain.