The six members of the insulin-like growth factor-binding protein family (IGFBP-1-6) are important components of the IGF (insulin-like growth factor) axis. In this capacity, they serve to regulate the activity of both IGF-I and -II polypeptide growth factors. The IGFBPs are able to enhance or inhibit the activity of IGFs in a cell- and tissue-specific manner. One of these proteins, IGFBP-5, also has an important role in controlling cell survival, differentiation and apoptosis. In this review, we report on the structural and functional features of the protein which are important for these effects. We also examine the regulation of IGFBP-5 expression and comment on its potential role in tumour biology, with special reference to work with breast cancer cells.

A panel of 12 Burkitt's lymphoma cell lines and four other B cell lines were tested for the presence of mutations in p53. Protein analysis using a mutant‐specific antibody and sequencing of both cDNA and genomic DNA revealed changes relative to the standard p53 protein sequence in 12 of the 16 lines studied, including 10 of the BL lines. Mutation of p53 in the BL lines was usually accompanied by loss of the other allele of p53. Testing of the mutated p53 cDNAs for gain of transforming activity or loss of growth suppression activity showed that several of the BL mutants were functionally altered from wild‐type p53.

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SummaryMaintenance of tissue boundaries is crucial for control of metastasis. We describe a new signalling pathway in which epithelial cell disruption can be minimised and thereby restricts epithelial-mesenchymal transgressions. This involves the release of insulin-like growth factor (IGF)-binding protein 5 (IGFBP5) from apoptotic cells, which increases the adhesion of epithelial cells on mesenchymal but not epithelial extracellular matrix (ECM), and involves the direct interaction of IGFBP5 and a2b1 integrins. IGFBP5 also induced cell adhesion to vitronectin in the absence of aVb3 integrin, the vitronectin receptor, again through an a2b1-integrin-dependent action, suggesting that IGFBP5 can induce spreading on matrices, even in the absence of the integrins normally used in this process. Using IGFBP5 mutants we demonstrate that the effect is IGF-independent but requires the heparin-binding domain in the C-terminus of IGFBP5. A truncated mutant containing only the C-terminal of IGFBP5 also induced adhesion. Adhesion induced by IGFBP5 was dependent on Cdc42 and resulted in activation of integrin-linked kinase (ILK) and Akt. Consistent with these changes, IGFBP5 facilitated prolonged cell survival in nutrient-poor conditions and decreased phosphorylation of the stress-activated kinase p38 MAPK (MAPK14). Whereas IGFBP5 enhanced adhesion, it inhibited cell migration, although this was not evident using the truncated Cterminal mutant, suggesting that effects of IGFBP5 on adhesion and migration involve different mechanisms. We anticipate that these responses to IGFBP5 would reduce the metastatic potential of cells.

We have previously reported that two highly conserved amino acids in the C-terminal domain of rat insulin-like growth factor-binding protein (

Summary Investigation of genetic changes in tumours by loss of heterozygosity (LOH) is a powerful technique for identifying chromosomal regions that may contain tumour suppressor genes. LOH has been described on chromosome 6 in ovarian carcinoma using restriction fragment length polymorphism analysis with a small number of probes. We studied 29 ovarian carcinomas with 19 probes mapping to chromosome 6. Sixteen of the 29 tumours showed LOH on 6q (55%). Of these 16, 63% showed loss of all informative markers on that arm. One tumour showed loss of 6q24-qter, localising the putative tumour suppressor gene to that region. Loss on 6p was 28% overall. However, using three dinucleotide repeat primer pairs from 6p to study LOH in seven (Friend et al., 1986), with the finding that a germline mutation constituted the first 'hit', to be followed by a second, somatic inactivation of the gene, which was usually detectable by RFLP analysis of filters of DNA from matched normal-tumour pairs. More recently, it has been shown that some families with retinoblastoma share a common mutation that can be traced from affected parent to affected child. In these cases, the other allele is lost or inactivated in various ways that differ in different affected family members (Phillips et al., 1991).For soine years there has been considerable cytogenetic evidence that in OC, one chromosome 6, particularly the long arm, is missing in part or in whole (Mitelman, 1991 seven had breakpoints between 6q21 -23, thus loss of the long arm telomeric to this region was the commonest single abnormality of chromosome 6 in this study. Despite the common occurrence of aneuploidy, Atkin et al. (1983) showed that one copy of 6q may be lost in early stage tumours, when the karotype is relatively undisturbed. These data have been followed up more recently by molecular studies of LOH that have broadly confirmed the cytogenetic findings (Ehlen & Dubeau, 1990;Lee et al., 1990).Further data are now needed to accurately define regions of LOH, so that efforts can be concentrated on cloning genes in the relevant region of chromosome 6. Therefore we have studied 29 pairs of matched malignant tumour and normal DNA with ten DNA markers that detect polymorphic sequences on 6q and six that do so on 6p. We also used the centromeric marker p308 (D6ZJ). Oka et al. (1991) showed that by using carefully dissected tumours it was possible to reliably demonstrate LOH by PCR. Subsequently dinucleotide (microsatellite) repeats mapping to chromosome 17 were used to successfully demonstrate LOH in breast cancer (Futreal et al., 1992). Therefore we included the dinucleotide repeats D6S89 and FTHPI, which were utilised to study the regions 6p22.3-23 and 6pl2-21 respectively by PCR-LOH. From the use of these eight 6p probes in all the tumours, we selected seven tumours for a more extensive analysis with three further dinucleotide repeats mapping to the region 6pl2-6p23. We also included 12 nonmalignant ovarian tissue specimens in our RFLP analysis. Although not all these samples wer...

The insulin-like growth factor (IGF) axis has been studied extensively in the developing vertebrate embryo. Knockout experiments have demonstrated that both IGF-I and -II are required for normal development in the mouse embryo, and mRNA and protein expression patterns for both growth factors, together with those for the type I IGF receptor and the six IGF-binding proteins, have been analysed in embryos from different species. Although the unique temporal and spatial expression patterns of these genes indicates important roles for the IGF axis during organ and whole animal development, the variation and complexity of expression makes these roles difficult to unravel. However, one possible mechanism unifying the IGF system in development is programmed cell death (apoptosis), which has been shown to be important in sculpting embryonic tissues, and, in particular, the developing limb bud. In addition, the very early onset of expression of various IGF family members in chicken embryos further emphasizes the fundamental importance of this system in development. This article reviews the work that has been carried out in this area in the context of current understanding of the IGF system.

We have used quantitative RT-PCR to analyse the mRNA expression profile of the major components of the IGF axis in different stages of murine mammary gland development, including late pregnancy, lactation and involution. We have shown that all the genes studied, IGF-I, IGF-II, IGF receptor (IGFR) and IGF-binding protein (IGFBP)-1 to -6, were expressed in every stage, albeit at greatly differing levels and displaying unique expression profiles between developmental stages. IGF-I was always expressed at significantly higher levels than either IGF-II or IGFR. This suggests that IGF-I may be the more important IGF during mammary morphogenesis. Overall, IGFBP-3 demonstrated the highest level of expression of any of the IGFBP genes throughout all the developmental stages studied. However, within developmental stages, by far the highest level of expression of any of the IGFBPs was that of IGFBP-5 at day 2 of involution; this was almost an order of magnitude higher than any of the other IGFBP levels recorded. This corroborated our previous findings that the levels of IGFBP-5 protein are highly elevated in the involuting mammary gland, and demonstrated that this up-regulation of IGFBP-5 operates at the level of transcriptional control or message stability. Comparison of the expression profile for these different genes would strongly suggest that they are likely to have differential functions throughout mammary gland development, and also highlights potential interactions and co-regulation between different members of this axis. In addition, our results have identified some similarities and differences in the expression of IGFBPs between the mouse mammary epithelial cell line, HC11, and the normal mammary gland which are worthy of study, most notably the differential regulation of IGFBP-2 and the site of expression of IGFBP-4 and -6. Overall, this study has demonstrated the importance and complexity of the IGF axis during mammary gland development and provides a valuable resource for future research in this area.