Heckman, B. M. et al. Crosstalk between the p190-B RhoGAP and IGF signaling pathways is required for embryonic mammary bud development. Dev. Biol. 309, 137-149

Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA.
Developmental Biology (Impact Factor: 3.55). 10/2007; 309(1):137-49. DOI: 10.1016/j.ydbio.2007.07.002
Source: PubMed


P190-B RhoGAP (p190-B, also known as ARHGAP5) has been shown to play an essential role in invasion of the terminal end buds (TEBs) into the surrounding fat pad during mammary gland ductal morphogenesis. Here we report that embryos with a homozygous p190-B gene deletion exhibit major defects in embryonic mammary bud development. Overall, p190-B-deficient buds were smaller in size, contained fewer cells, and displayed characteristics of impaired mesenchymal proliferation and differentiation. Consistent with the reported effects of p190-B deletion on IGF-1R signaling, IGF-1R-deficient embryos also displayed a similar small mammary bud phenotype. However, unlike the p190-B-deficient embryos, the IGF-1R-deficient embryos exhibited decreased epithelial proliferation and did not display mesenchymal defects. Because both IGF and p190-B signaling affect IRS-1/2, we examined IRS-1/2 double knockout embryonic mammary buds. These embryos displayed major defects similar to the p190-B-deficient embryos including smaller bud size. Importantly, like the p190-B-deficient buds, proliferation of the IRS-1/2-deficient mesenchyme was impaired. These results indicate that IGF signaling through p190-B and IRS proteins is critical for mammary bud formation and ensuing epithelial-mesenchymal interactions necessary to sustain mammary bud morphogenesis.

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Available from: Tracy Vargo-Gogola
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    • "Both IRS1 and IRS2 were previously shown to play important roles during embryonic MG development (Chan and Lee, 2008; Heckman et al., 2007). Postnatally, both Irs1 and Irs2 null MGs are normal, possibly because they compensate for each other (Chan and Lee, 2008; Heckman et al., 2007). We previously generated Irs1/Irs2 double conditional knockout mice with the R26YFP reporter (Irs1 L/L ;Irs2 L/L ;R26YFP) and used K14-Cre and MMTV-Cre mouse lines to disrupt them in MECs (Figure S3A). "
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    Full-text · Article · Jun 2014 · Stem Cell Reports
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    • "P190B Rho GTPase activating protein (GAP), an important regulator of Rac and RhoA, functions as a negative regulator by accelerating GTP hydrolysis [15], [16]. Our previous studies have shown that p190B plays a crucial role in the developing embryonic and postnatal mammary gland [17], [18], and intriguingly, that it has pro-tumorigenic functions during MMTV-Neu induced mammary tumor formation [19], [20]. Furthermore, we have demonstrated that p190B overexpression in the developing mammary gland promotes aberrant terminal end bud (TEB) morphogenesis and hyperbranching in association with alterations in the adjacent stroma [18]. "
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    ABSTRACT: Rho GTPases mediate stromal-epithelial interactions that are important for mammary epithelial cell (MEC) morphogenesis. Increased extracellular matrix (ECM) deposition and reorganization affect MEC morphogenesis in a Rho GTPase-dependent manner. Although the effects of altered ECM on MEC morphogenesis have been described, how MECs regulate stromal deposition is not well understood. Previously, we showed that p190B RhoGAP overexpression disrupts mammary gland morphogenesis by inducing hyperbranching in association with stromal alterations. We therefore hypothesized that MEC overexpression of p190B regulates paracrine interactions to impact fibroblast activation. Using a combination of in vivo morphometric and immunohistochemical analyses and primary cell culture assays, we found that p190B overexpression in MECs activates fibroblasts leading to increased collagen, fibronectin, and laminin production and elevated expression of the collagen crosslinking enzyme lysyl oxidase. Phosphorylation of the TGF-β effector SMAD2 and expression of the TGF-β target gene αSma were increased in p190B-associated fibroblasts, suggesting that elevated TGF-β signaling promoted fibroblast activation. Mechanical tension and TGF-β cooperate to activate fibroblasts. Interestingly, active TGF-β was elevated in conditioned medium from p190B overexpressing MECs compared to control MECs, and p190B overexpressing MECs exhibited increased contractility in a collagen gel contraction assay. These data suggest that paracrine signaling from the p190B overexpressing MECs may activate TGF-β signaling in adjacent fibroblasts. In support of this, transfer of conditioned medium from p190B overexpressing MECs onto wildtype fibroblasts or co-culture of p190B overexpressing MECs with wildtype fibroblasts increased SMAD2 phosphorylation and mRNA expression of ECM genes in the fibroblasts when compared to fibroblasts treated with control CM or co-cultured with control MECs. The increased ECM gene expression and SMAD2 phosphorylation were blocked by treatment with a TGF-β receptor inhibitor. Taken together, these data suggest that p190B overexpression in the mammary epithelium induces fibroblast activation via elevated TGF-β paracrine signaling.
    Full-text · Article · May 2013 · PLoS ONE
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    • "Dlk1, an endogenous inhibitor of Notch, could act to repress Notch signals in the mammary primordial epithelium; Notch controls cell fate and tissue homeostasis in postnatal mammary epithelium and could be regulating stem cell function from the time that they arise [46]. Other genes of interest include Arhgap28 and Centd3 since another Rho-GTPase activating protein-encoding gene, Arhgap5, has been shown to regulate epithelial-mesenchymal interactions necessary to sustain mammary bud morphogenesis [47]. "
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