Germ line knockout of IGFBP-3 reveals influences of the gene on mammary gland neoplasia

Abstract

Insulin-like growth factor binding protein-3 (IGFBP-3) is an important carrier protein for insulin-like growth factors (IGFs) in the circulation. IGFBP-3 antagonizes the growth-promoting and anti-apoptotic activities of IGFs in experimental systems, but in certain contexts can increase IGF bioactivity, probably by increasing its half-life. The goal of this study was to investigate the role of IGFBP-3 in breast carcinogenesis and breast cancer metastasis. In the first part of the study, we exposed IGFBP-3 knockout and wild-type female mice to dimethylbenz[a]anthracene (DMBA) and followed them for appearance of primary tumors for up to 13 months. In the second part, mice of each genotype received an IV injection of 4T1 mammary carcinoma cells and then lung nodules were counted. Our results show that IGFBP-3 knockout mice developed breast tumors significantly earlier than the wild-type (13.9 ± 1.1 versus 22.5 ± 3.3 weeks, respectively, P = 0.0144), suggesting tumor suppression activity of IGFBP-3. In tumors of IGFBP-3 knockout mice, levels of phospho-AKT(Ser473) were increased compared to wild-type mice. The lung metastasis assay showed significantly more and larger lung nodules in IGFBP-3 knockout mice than in wild-type mice. While we observed increased levels of IGFBP-5 protein in the IGFBP-3 knockout mice, our findings suggest that this was not sufficient to completely compensate for the absence of IGFBP-3. Even though knockout of IGFBP-3 is associated with only a subtle phenotype under control conditions, our results reveal that loss of this gene has measurable effects on breast carcinogenesis and breast cancer metastasis.

Insulin-like growth factor binding protein-3 links obesity and breast cancer progression

“…This is consistent with another recent study employing a global deletion of IGFBP-3 in female mice [32] but contrasts with two other studies in which decreased circulating IGF-1 levels were observed in male IGFBP-3 knockout mice [19, 20]. The difference in the relationship between circulating IGF-1 and the presence of IGFBP-3 between male and female mice suggests the possibility that the compensatory effects that act to maintain IGF-1 levels in the absence of IGFBP-3 are gender-specific.…”

“…A major finding is that not only high-fat feeding, but also host-derived IGFBP-3, stimulated mammary tumor growth. This differs from the observation, in a different BP3KO model, that chemical carcinogen-induced mammary tumors grew more rapidly than in corresponding wild-type mice [32]. …”

“…The difference in the relationship between circulating IGF-1 and the presence of IGFBP-3 between male and female mice suggests the possibility that the compensatory effects that act to maintain IGF-1 levels in the absence of IGFBP-3 are gender-specific. The expression of other IGF binding proteins was not examined in this study, so possible compensatory IGFBP changes that might act to stabilize and transport IGF-1 in the absence of IGFBP-3 remain unknown, since circulating levels of IGFBP-2 and IGFBP-5 were unchanged in a previous study of IGFBP-3 knockout mice [32]. …”

Metastasis-associated protein 1 is an upstream regulator of DNMT3a and stimulator of insulin-growth factor binding protein-3 in breast cancer

“…Apart from being involved in the cancer progression, low levels of DNMT3a could result in an unscheduled activation of EPAS1 gene which contributes to cell survival under extreme hypoxic conditions10. In addition to cancer progression, DNMT3a may be a negative regulator of tyrosine hydroxylase (TH1) as paraventricular nucleus of the hypothalamus (PVH) in Sim1-specific Dnmt3a deletion mice exhibits an elevated TH level3536. In this context, it is interesting to note that MTA1 - also an repressor of DNMT3a (this study), acts as a coactivator of TH transcription in neuronal cells35.…”

“…Interesting, in addition to MTA1, IGFBP3 is also overexpressed in many other human cancers [13; 36; 37]. However, results from IGFBP3 −/− knockout mice shows an accelerated tumor growth as compared to the wild type mice, suggesting anti-oncogenic role of IGFBP3 in this specific experimental model36. Thus, IGFBP3 may contribute to its growth inhibitory function in both insulin-like growth factor-dependent and -independent manner.…”