Presence of RON receptor tyrosine kinase and its splicing variant in malignant and non-malignant human colonic mucosa

The presence of RON and its variant isoform in malignant and non-malignant human colonic tissues was examined by immunohistochemistry using paraffin-e mbedded sections and RT-PCR analysis followed by direct sequencing of PCR p roduct using RNAs isolated from frozen tissues. In normal colonic mucosa, R ON was uniformly expressed in crypt cells, especially in the bottom of cryp ta. On the other hand, the expression was distributed heterogeneously in ad enomas and in colon cancer. The expression of RON was significantly related to the degree of differentiation of colon cancer and the deletion of the e xpression was observed in colon cancer specimens with high incidence. The R T-PCR analysis of RNA isolated from non-malignant and malignant colonic tis sue revealed the presence of two RON mRNA isoforms with 432-bp and 286-bp. Direct sequecing of major product of 432-bp was revealed to be identical to that of human wild-type RON. On the other hand, major product of 286-bp wa s revealed to be almost identical to that of a splicing variant of RON tran script which has been found in human gastric cancer cell line, KATO-III. Th e results obtained in this study may indicate that both wild-type RON and i ts variant isoform play an important role in regulating the normal function of colonic mucosa such as differentiation and motile activity and the expr ession of both wild-type RON and its variant isoform could be considered to be reduced during malignancy of human colonic mucosa.