Identification of a novel activated form of the keratinocyte growth factor receptor by expression cloning from parathyroid adenoma tissue

Abstract

Parathyroid adenomas are benign tumors in the parathyroid glands, whose pathogenesis is largely unknown. We utilized an expression cDNA cloning strategy to identify oncogenes activated in parathyroid adenomas. An expression cDNA library was prepared directly from a clinical sample of parathyroid adenoma tissue, transfected into NIH3T3 cells, and foci of morphologically transformed cells were isolated. Following plasmid rescue, we identi®ed cDNAs for the keratinocyte growth factor receptor at a high frequency. Interestingly, approximately half of the clones encoded a variant receptor containing an altered C-terminus. Analysis of the transforming activity of the variant receptor revealed that the altered C-terminus upregulated the transforming activity in a ligand-independent manner. The higher transforming activity was not accompanied by increase of dimerization or overall autophosphorylation of the receptor. However, tyrosine phosphorylation of downstream receptor substrates, including Shc isoforms and possibly FRS2, are increased in the transfectants expressing the parathyroid tumorderived receptor. Genomic analysis showed that a previously unidenti®ed exon was used to form the novel isoform. This alternative splicing appears to occur preferentially in parathyroid adenomas.

Fibroblast growth factor 23 reduces expression of type IIa Na+/Pi co‐transporter by signaling through a receptor functionally distinct from the known FGFRs in opossum kidney cells

“…For expression using retrovirus, we have constructed human wild‐type FGFR2(IIIc) ( FGFR2 ( WT )) (Sakaguchi et al . 1999b), and dominant‐negative FGFR2(IIIc) ( FGFR2 ( DN )) linked to the enhanced green fluorescent protein ( EGFP ) through the IRES (internal ribosomal entry site) sequence in the pMXs‐IG vector (a gift from Dr Kitamura, University of Tokyo).…”

Inhibition of human bladder tumour cell growth by fibroblast growth factor receptor 2b is independent of its kinase activity. Involvement of the carboxy-terminal region of the receptor

“…Two isoforms of the receptor, FGFR2b and Ksam-IIC3, which differ in the carboxy-terminal domain, have been described and have very different growth-activating properties (Ishii et al, 1995;Lorenzi et al, 1997;Sakaguchi et al, 1999). We therefore investigated the growth inhibitory properties of Ksam-IIC3, the isoform with the short carboxy-terminal domain (Figure 4a).…”

Truncated FGFR2 is a clinically actionable oncogene in multiple cancers

“…Two more FGFR2 isoforms make use of an alternative E18. The encoded C termini either overlap with the proximal part of the canonical FGFR2 C terminus (C2) or are different to it (C4) [16][17][18] . Thus, splicing to E18-C3 or E18-C4 generates FGFR2 isoforms that encode dysfunctional C termini resembling E18 truncation (Extended Data Fig.…”

“…Previous research showed in vitro transforming abilities of C-terminally truncated FGFR2 isoforms [17][18][19][25][26][27] . Our in vivo screening data and analyses of human oncogenomic datasets similarly suggested that exclusion of E18 is a critical determinant to render FGFR2 REs oncogenic.…”

“…FGFR2 is a receptor tyrosine kinase (RTK) that consists of an extracellular ligand-binding domain, intracellular tyrosine kinase domains and a carboxy (C)-terminal tail relevant for receptor activity fine-tuning 14 . In human cancers, FGFR2 can be affected by hotspot mutations and structural variants, namely fusions and amplifications 1 , some of which produce truncated FGFR2 isoforms [15][16][17][18][19] . FGFR2 structural variants have been considered to be oncogenic and actionable due to the resulting overexpression and increased stabilization of the receptor 2,[20][21][22] .…”