IFN‐γ regulation of vacuolar pH, cathepsin D processing and autophagy in mammary epithelial cells

Department of Surgery, Northwestern University Feinberg School of Medicine, Chicago, Illinois 60614-3394
Journal of Cellular Biochemistry (Impact Factor: 3.26). 09/2008; 105(1):208 - 218. DOI: 10.1002/jcb.21814


In this study we examined the ability of interferon-γ (IFN-γ) to regulate mammary epithelial cell growth and gene expression, with particular emphasis on two genes: Maspin (a member of serine protease inhibitor superfamily), and the lysosomal aspartyl endopeptidase cathepsin D (CatD). The protein products of these genes are critically involved in regulation of multitude of biological functions in different stages of mammary tissue development and remodeling. In addition, the expression of Maspin is down-regulated in primary breast cancer and is lost in metastatic disease, while CatD is excessively produced and aberrantly secreted by breast cancer cells. We report that IFN-γ receptors are expressed in mammary epithelial cells, and receptor engagement by IFN-γ transduces the IFN-γ signal via Stat-1 resulting in decreased vacuolar pH. This change in vacuolar pH alters CatD protein processing and secretion concurrent with increased Maspin secretion. In addition, IFN-γ exerts a suppressive effect on cell growth and proliferation, and induces morphological changes in mammary epithelial cells. Our studies also reveal that breast cancer cells, which are devoid of Maspin, are refractory to IFN-γ with respect to changes in vacuolar pH and CatD. However, Maspin transfection of breast cancer cells partially sensitizes the cells to IFN-γ's effect, thus providing new therapeutic implications. J. Cell. Biochem. 105: 208–218, 2008. © 2008 Wiley-Liss, Inc.

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    • "Corroborating the activation of IFNgR signaling in luminal cells, we also observed enriched expression of IFNgR1 in the luminal fraction of organoids (Figure S6C). This is in keeping with previous studies showing IFNgR1 and IFNgR2 expression in cultured normal human mammary epithelial cells, which represent a mixture of luminal and basal cell populations based on their cytokeratin expression (Khalkhali-Ellis et al., 2008), while proteomic profiling revealed that IFNgR1 is present only on a subset of luminal progenitors in vivo (Ji et al., 2011). Functionally, we found that incubation of organoids with IFNg inhibited branching (Figure 6C), confirming an inhibitory role for IFNg in mammary morphogenesis. "
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    • "Although limited data exist on the role of proinflammatory cytokines in the human breast, IFNγ has been reported to be present in the breast during development and milk production [48]. In vitro studies have shown that human mammary epithelial cells contain the IFNγ receptor and are sensitive to IFN-γ stimulation, resulting in inhibition of proliferation, disruption of cell polarity and tight junctions; all are critical steps in milk stasis, involution and tissue remodeling during outgrowth [49-51]. Therefore, the presence of IFNγ during stages of breast tissue remodeling suggests the potential for monocyte/macrophage exposure in breast tissue, and a role for IFN-γ in breast function. "
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    • "A massive breakdown of lysosomes could cause cell death by necrosis, which is related to increase of cytosolic acidification [10]. IFN-γ can regulate lysosome activities by the alteration of vacuolar pH or the activation of cathepsin expression to cause cell death [23], [24]. Here we found no significant increase in hepatocytes' acidification and protein level of cathepsin B/L upon IFN-γ stimulation. "
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