A tumor-associated fibronectin isoform generated by alternative splicing of messenger RNA precursors.

Abstract

Abstract. Fibronectin (FN) represents the mixture of a number of structurally different molecules (isoforms) whose make-up varies depending on the FN sources. FN from cultured transformed human cells has a very different isoform composition with respect to its normal counterpart. In fact, SV-40-transformed WI-38VAI3 human fibroblasts produce high levels of a FN isoform (B-FN) which is very poorly expressed in their normal, WI-38, counterpart. We have recently demonstrated that the B-FN isoform derives from a differential splicing pattern of the FN primary transcript which leads, in transformed cells, to a high level expression of the exon ED-B (Zardi, L., B. Carnemolla, A. Siri, T. E. Petersen, G. Paolella, G. Sebastio, and F. E. . EMBO (Eur. Mol. Biol. Organ.) J. 6:2337-2342). Here we report on the production and characterization of a monoclonal antibody (BC-1) which recognizes an epitope within the protein sequence coded for by the ED-B exon. This monoclonal antibody makes it possible to carry out immunohistochemical analysis of the distribution of the ED-B-containing FN isoform (B-FN) in human tissues. The results show that while in normal, adult, human tissues total FN has a widespread distribution, the B-FN isoform is restricted only to synovial cells, to some vessels and areas of the interstitium of the ovary, and to the myometrium. On the contrary, the B-FN isoform has a much greater expression in fetal and tumor tissues. These results demonstrate that, in vivo, different FN isoforms have a differential distribution and indicate that the B-FN isoform may play a role in ontogenesis and oncogenetic processes. It has been previously demonstrated that FN polymorphism is at least partially caused by alternative splicing schemes in three regions of the primary transcript of a single gene which may generate 20 different FN subunit isoforms (18,19,29). One of these regions (IIICS, see Fig. 1 A) is between the last two type lZI homology repeats; a single exon is subdivided to yield five alternative patterns of splicing. Hynes and co-workers (34) showed that inclusion of the IIICS sequence contributed to the differences in size between the larger and smaller subunit of plasma FN. Humphries et At the second region of variation (ED-A), a single exon encoding a complete type III repeat is either included or omitted from the mature mRNA. This variation is tissue specific and the ED-A sequence is absent in the mRNA of liver (10,20,21) which is the source of plasma FN (38). Using a rabbit antiserum to the rat ED-A segment, Paul et al. (31) At the third region of variation (ED-B), a single exon encoding a complete type III repeat is either included or omitted from the mature mRNA (14,33,44). The ED-B sequence presents two interesting peculiarities: (a) it is the more conserved FN region, 100 and 96% homology with rat and chicken FN, respectively (28,44); and (b) this exon is highly expressed in transformed human cells, while it is barely de-

Characterisation and radioimmunotherapy of L19-SIP, an anti-angiogenic antibody against the extra domain B of fibronectin, in colorectal tumour models

“…This is supported by other studies in different tumour types (Zardi et al, 1987;Carnemolla et al, 1989;Castellani et al, 1994;Kaczmarek et al, 1994;Neri et al, 1997;D'Ovidio et al, 1998;Kosmehl et al, 1999;Tarli et al, 1999;Viti et al, 1999;Ebbinghaus et al, 2004).…”

“…However, it is overexpressed during active tissue remodelling, for example, angiogenesis in tumours, wound healing and embryogenesis Kaspar et al, 2006). It has been shown to accumulate specifically around neovasculature in studies of many different tumour types, making it a good marker for angiogenesis (Carnemolla et al, 1989;Kaczmarek et al, 1994;Neri et al, 1997;Kosmehl et al, 1999;Tarli et al, 1999;Viti et al, 1999;Demartis et al, 2001;Castellani et al, 2002;Birchler et al, 2003;Ebbinghaus et al, 2004).…”

Human amnion epithelial cells assemble tenascins and three fibronectin isoforms in the extracellular matrix

“…Human embryonal skin fibroblasts were obtained from a local source and were cultured as above. In some experiments the cells were exposed to monensin (1 PM; Eli Lily, Indianapolis, IN) for 16 h to prevent cellular secretion [15,16] [19], BC-1 reacting with EDBcFn [20,21] and FDC-6 reacting with an oncofetal epitope in type III connecting segment region of cFn [22] have been characterized earlier.…”

Involvement of Large Tenascin-C Splice Variants in Breast Cancer Progression

“…[17][18][19][20][21] The size of Tn-C monomers varies as a result of alternative splicing in the FN III repeats at the pre-mRNA level. There are eight conserved FN III repeats (designated as numbers [1][2][3][4][5][6][7][8] and, in the case of human Tn-C, up to nine alternatively spliced FN III repeats (designated as letters A-D) inserted between the conserved repeats 5 and 6. In adults, the smallest Tn-C variant in which the alternatively spliced domain is spliced out is present in static tissues such as cartilage, 22 whereas large variants containing the alternatively spliced FNIII domains in various combinations are found in developing tissues [23][24][25] and in pathological tissues which undergo remodeling, as with regeneration, inflammation, and tumorigenesis.…”