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Cyclic AMP regulates formation of mammary epithelial acini in vitro.

ABSTRACT: Epithelial cells form tubular and acinar structures notable for a hollow lumen. In three-dimensional culture utilizing MCF10A mammary epithelial cells, acini form due to integrin-dependent polarization and survival of cells contacting extracellular matrix (ECM), and the apoptosis of inner cells of acini lacking contact with the ECM. In this paper, we report that cyclic AMP (cAMP)-dependent protein kinase A (PKA) promotes acinus formation via two mechanisms. First, cAMP accelerates redistribution of ?6-integrin to the periphery of the acinus and thus facilitates the polarization of outer acinar cells. Blocking of ?6-integrin function by inhibitory antibody prevents cAMP-dependent polarization. Second, cAMP promotes the death of inner cells occupying the lumen. In the absence of cAMP, apoptosis is delayed, resulting in perturbed luminal clearance. cAMP-dependent apoptosis is accompanied by a posttranscriptional PKA-dependent increase in the proapoptotic protein Bcl-2 interacting mediator of cell death. These data demonstrate that cAMP regulates lumen formation in mammary epithelial cells in vitro, both through acceleration of polarization of outer cells and apoptosis of inner cells of the acinus.

SUBMITTER: Nedvetsky PI

PROVIDER: S-EPMC3408423 | biostudies-literature | 2012 Aug

REPOSITORIES: biostudies-literature

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Cyclic AMP regulates formation of mammary epithelial acini in vitro.

Nedvetsky Pavel I PI Kwon Sang-Ho SH Debnath Jayanta J Mostov Keith E KE

Molecular biology of the cell 20120606 15

Epithelial cells form tubular and acinar structures notable for a hollow lumen. In three-dimensional culture utilizing MCF10A mammary epithelial cells, acini form due to integrin-dependent polarization and survival of cells contacting extracellular matrix (ECM), and the apoptosis of inner cells of acini lacking contact with the ECM. In this paper, we report that cyclic AMP (cAMP)-dependent protein kinase A (PKA) promotes acinus formation via two mechanisms. First, cAMP accelerates redistribution ...[more]

PMID: 22675028

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Project description:BackgroundMyocardin-related transcription factors (MRTF) A and B link actin dynamics and mechanotransduction to gene expression. In mice, MRTF-A is involved in mammary gland differentiation, but its role in human mammary epithelial cells remains unclear.MethodsThree-dimensional cultures of human mammary epithelial MCF10A cells were used to model acinar morphogenesis. Stable MRTF-A knockdown, MRTF-A/B rescue and MRTF-A/B overexpression was established to characterize the functional role during morphogenesis using confocal microscopy and expression analysis. Breast cancer patient databases were analyzed for MRTF-A expression.ResultsWe showed that a precise temporal control of MRTFs is required for normal morphogenesis of MCF10A mammary acini. MRTF transcriptional activity, but not their protein amounts, is transiently induced during 3D acini formation. MRTF-A knockdown dramatically reduces acini size and prevents lumen formation. These effects are rescued by re-expression of MRTF-A, and partially by MRTF-B. Conversely, overexpression of MRTF-A and MRTF-B increases acini size, resulting in irregular spheroids without lumen and defective apico-basal polarity. These phenotypes correlate with deregulated expression of cell cycle inhibitors p21/Waf1, p27/Kip1 and altered phosphorylation of retinoblastoma protein. In MRTF overexpressing spheroids, proliferation and apoptosis are simultaneously increased at late stages, whilst neither occurs in control acini. MRTFs interfere with anoikis of the inner cells and cause an integrin switch from α6 to α5, repression of E-cadherin and induction of mesenchymal markers vimentin, Snai2 and Zeb1. Moreover, MRTF-overexpressing spheroids are insensitive to alteration in matrix stiffness. In two breast cancer cohorts, high expression of MRTF-A and known target genes was associated with decreased patient survival.ConclusionMRTF-A is required for proliferation and formation of mammary acini from luminal epithelial cells. Conversely, elevated MRTF activity results in pre-malignant spheroid formation due to defective proliferation, polarity loss and epithelial-mesenchymal transition.

Project description:INT6/EIF3E has been implicated in breast tumorigenesis, but its functional activities remain poorly defined. We found that, repressing INT6 expression induced transformed properties in normal human mammary epithelium (MCF10A); in contrast, Int6 silencing induced apoptosis in HeLa cells. As in fission yeast, Int6 in human cells was required for assembly of active proteasomes. A reverse-phase protein array screen identified SRC3/AIB1 as one oncoprotein the level and stability of which increased when Int6 was silenced in MCF10A cells. Our data further show that Int6 binds SRC3 and its ubiquitin ligase Fbw7, thus perhaps mediating the interaction between SRC3-Fbw7 and proteasomes. Consistent with this, Int6 silencing did not increase SRC3 levels in HeLa cells, which have low Fbw7 levels. It is surprising that, however, polyubiquitylated proteins do not accumulate or may even decrease in Int6-silenced cells that contain defective proteasomes. Considering that decreased ubiquitin might explain this observation and that Int6 might control ubiquitin levels in its role as a subunit of eIF3 (eukaryote translation initiation factor 3), we found that silencing Int6 reduced monoubiquitin protein levels, which correlated with a shift of ubiquitin mRNAs from larger polysomes to non-translating ribosomes. In contrast, levels of many housekeeping proteins did not change. This apparent reduction in the translation of ubiquitin genes correlated with a modest reduction in protein synthesis rate and formation of large polysomes. To further determine whether Int6 can selectively control translation, we analyzed translation of different 5'-untranslated region reporters and found that indeed, loss of Int6 had differential effects on these reporters. Together the data suggest that Int6 depletion blocks ubiquitin-dependent proteolysis by decreasing both ubiquitin levels and the assembly of functional proteasome machinery, leading to accumulation of oncoproteins, such as SRC3 that can transform mammary epithelium. Our data also raise the possibility that Int6 can further fine-tune protein levels by selectively controlling translation of specific mRNAs.

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Cyclic AMP regulates formation of mammary epithelial acini in vitro.

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Cyclic AMP regulates formation of mammary epithelial acini in vitro.

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