Deletion or insertion in the first immunoglobulin-plexin-transcription (IPT) domain differentially regulates expression and tumorigenic activities of RON receptor Tyrosine Kinase

Qi Ma,Ming-Hai Wang,Sunny Guin,Kun Zhang,Yong-Qing Zhou

doi:10.1186/1476-4598-9-307

Abstract

BackgroundActivation of the RON receptor tyrosine kinase, a member of the c-MET family, regulates tumorigenic phenotypes. The RON extracellular domains are critical in regulating these activities. The objective of this study was to determine the role of the first IPT domain in regulating RON-mediated tumorigenic activities and the underlying mechanisms.ResultsTwo RON variants, RON160 and RONE5/6in with deletion and insertion in the first IPT domain, respectively, were molecularly cloned. RON160 was a splicing variant generated by deletion of 109 amino acids encoded by exons 5 and 6. In contrast, RONE5/6in was derived from a transcript with an insertion of 20 amino acids between exons 5 and 6. Both RON160 and RONE5/6in were proteolytically matured into two-chain receptor and expressed on the cell surface. RON160 was constitutively active with tyrosine phosphorylation. However, activation of RONE5/6in required ligand stimulation. Deletion resulted in the resistance of RON160 to proteolytic digestion by cell associated trypsin-like enzymes. RON160 also resisted anti-RON antibody-induced receptor internalization. These features contributed to sustained intracellular signaling cascades. On the other hand, RONE5/6in was highly susceptible to protease digestion, which led to formation of a truncated variant known as RONp110. RONE5/6in also underwent rapid internalization upon anti-RON antibody treatment, which led to signaling attenuation. Although ligand-induced activation of RONE5/6in partially caused epithelial to mesenchymal transition (EMT), it was RON160 that showed cell-transforming activities in cell focus formation and anchorage-independent growth. RON160-mediated EMT is also associated with increased motile/invasive activity.ConclusionsAlterations in the first IPT domain in extracellular region differentially regulate RON mediated tumorigenic activities. Deletion of the first IPT results in formation of oncogenic variant RON160. Enhanced degradation and internalization with attenuated signaling cascades could be the mechanisms underlying non-tumorigenic features of RONE5/6in.

Highlights

Activation of the RON receptor tyrosine kinase, a member of the c-MET family, regulates tumorigenic phenotypes
Different RON mRNA transcripts with alterations in the first IPT unit are present in colon, breast, and pancreatic cancer cells Previous studies have shown that deletion of the first IPT unit coded by exons 5 and 6 results in formation of oncogenic variant RON160 [13]
To determine if other types of alterations exists in the first IPT unit, total RNA isolated from a panel of twelve cancer cell lines was subjected to Reverse Transcription (RT)-Polymerase chain reaction (PCR) analysis

Summary

Introduction

Activation of the RON receptor tyrosine kinase, a member of the c-MET family, regulates tumorigenic phenotypes. The RON (recepteur d’origine nantais) receptor tyrosine kinase belongs to the MET proto-oncogene family [1,2], which plays a critical role in epithelial cell homeostasis and tumorigenic development [3]. Evidence has indicated that altered RON expression results in increased survival and pro-apoptotic activity of tumor cells [18,19]. We have recently observed that down-regulation of RON expression under chronic hypoxia is a mechanism contributing to the insensitivity of tumor cells towards small molecule inhibitor-induced inhibitory or cytotoxic activities [22]. Aberrant RON expression is a pathogenic factor contributing to cancer development and malignant progression. Such abnormality provides the molecular basis of targeting RON for potential therapeutic intervention [23]

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