Altered expression of the RON receptor tyrosine kinase in primary human colorectal adenocarcinomas: generation of different splicing RON variants and their oncogenic potential

Abstract

The RON receptor tyrosine kinase is a member of the MET proto-oncogene family that has been implicated in regulating motile-invasive phenotypes in certain types of epithelial cancers. The purpose of this study was to determine if RON expression is altered in primary human colorectal adenocarcinomas. Results from immunohistochemical staining showed that RON is highly expressed in the majority of colorectal adenocarcinomas (29/49 cases). Accumulated RON is also constitutively active with autophosphorylation in tyrosine residues. Moreover, three splicing variants of RON, namely ROND165, ROND160, and ROND155 were detected and cloned from two primary colon cancer samples. These RON variants were generated by deletions in different regions in extracellular domains of the RON b chain. Functional studies showed that expression of ROND160 or ROND155 in MartinDarby canine kidney cells resulted in increased cell dissociation (scatter-like activity). RON variants, ROND160 and ROND155, also exerted the ability to induce multiple focus formation and sustain anchorageindependent growth of transfected NIH3T3 cells. Moreover, NIH3T3 cells expressing ROND160 or ROND155 formed tumors in athymic nude mice and colonized in the lungs. These data suggest that RON expression is altered in certain primary colon cancers. Abnormal accumulation of RON variants may play a role in the progression of certain colorectal cancers in vivo.

Aberrant activation of ALK kinase by a novel truncated form ALK protein in neuroblastoma

“…25 The recepteur d'origine nantais (RON) RTK variant with a deletion in the first immunoglobulinplexin transcription domain (ROND160) has also been considered as a constitutively activated kinase in several human cancers. 20,26 RON belongs to the MET proto-oncogene family, which plays a critical role in epithelial cell homeostasis and tumorigenic development. 27 ROND160 is derived from a RON mRNA transcript by alternative splicing that eliminates 109 aa residues from the extracellular domain of RON b-chain and is expressed in 450% of primary colon cancers and 90% of brain tumors, but not in any normal tissues.…”

“…27 ROND160 is derived from a RON mRNA transcript by alternative splicing that eliminates 109 aa residues from the extracellular domain of RON b-chain and is expressed in 450% of primary colon cancers and 90% of brain tumors, but not in any normal tissues. 26,28 The deleted 109 aa residues are encoded by exons 5/6, which constitute the first immunoglobulin-plexin transcription domain in the RON b-chain. 26,28 The mechanism for the oncogenic activation of ROND160 is believed to be one in which the deletion in the extracellular domain causes conformational changes in the kinase and leads to spontaneous dimerization, which in turn causes constitutive receptor phosphorylation and increased intracellular signaling activation.…”

“…26,28 The deleted 109 aa residues are encoded by exons 5/6, which constitute the first immunoglobulin-plexin transcription domain in the RON b-chain. 26,28 The mechanism for the oncogenic activation of ROND160 is believed to be one in which the deletion in the extracellular domain causes conformational changes in the kinase and leads to spontaneous dimerization, which in turn causes constitutive receptor phosphorylation and increased intracellular signaling activation. 26,28,29 The ALK del2-3 variant consists of a 282-bp in-frame deletion of ALK that corresponds to 224 --318 aa in the first MAM domain (Figure 1d).…”

New tools for dissecting RON receptor tyrosine kinase oncogenic signaling

“…RON activation typically results in triggering of the ras/ mitogen-activated protein kinase (MAPK), phosphatidyl inositol-3 kinase (PI-3K)/Akt, and focal adhesion kinase (FAK) signaling pathways. Overexpression of the receptor has been observed in a variety of cancers including colorectal adenocarcinomas 13 and carcinomas of the ovaries, 10 bladder 14 and breast. 15,16 In addition, ligand-independent activation of RON has been observed in various cancer samples.…”

“…15,16 In addition, ligand-independent activation of RON has been observed in various cancer samples. 13,17,18 For example, omission of the first IPT domain of RON through an aberrant mRNA splicing event which result in an in frame splice variant (RON∆160) produces a constitutively activated version of RON capable of cellular transforming activities in the absence of ligand. 13,19 However, the mechanisms by which this splice variant transforms immortalized rodent fibroblasts remains unclear.…”