Miz1 Deficiency in the Mammary Gland Causes a Lactation Defect by Attenuated Stat5 Expression and Phosphorylation

Miz1 is a zinc finger transcription factor with an N-terminal POZ domain. Complexes with Myc, Bcl-6 or Gfi-1 repress expression of genes like Cdkn2b (p15(Ink4)) or Cd-kn1a (p21(Cip1)). The role of Miz1 in normal mammary gland development has not been addressed so far. Conditional knockout of the Miz1 POZ domain in luminal cells during pregnancy caused a lactation defect with a transient reduction of glandular tissue, reduced proliferation and attenuated differentiation. This was recapitulated in vitro using mouse mammary gland derived HC11 cells. Further analysis revealed decreased Stat5 activity in Miz1 Delta POZ mammary glands and an attenuated expression of Stat5 targets. Gene expression of the Prolactin receptor (PrlR) and ErbB4, both critical for Stat5 phosphorylation (pStat5) or pStat5 nuclear translocation, was decreased in Miz1 Delta POZ females. Microarray, ChIP-Seq and gene set enrichment analysis revealed a down-regulation of Miz1 target genes being involved in vesicular transport processes. Our data suggest that deranged intracellular transport and localization of PrlR and ErbB4 disrupt the Stat5 signalling pathway in mutant glands and cause the observed lactation phenotype

Adult stem cells at work: regenerating skeletal muscle

Skeletal muscle regeneration is a finely tuned process involving the activation of various cellular and molecular processes. Satellite cells, the stem cells of skeletal muscle, are indispensable for skeletal muscle regeneration. Their functionality is critically modulated by intrinsic signaling pathways as well as by interactions with the stem cell niche. Here, we discuss the properties of satellite cells, including heterogeneity regarding gene expression and/or their phenotypic traits and the contribution of satellite cells to skeletal muscle regeneration. We also summarize the process of regeneration with a specific emphasis on signaling pathways, cytoskeletal rearrangements, the importance of miRNAs, and the contribution of non-satellite cells such as immune cells, fibro-adipogenic progenitor cells, and PW1-positive/Pax7-negative interstitial cells

A dysfunctional miR-1-TRPS1-MYOG axis drives ERMS by suppressing terminal myogenic differentiation

Rhabdomyosarcoma is the most common pediatric soft tissue tumor, comprising two major subtypes: the PAX3/7-FOXO1 fusion-negative embryonal and the PAX3/7-FOXO1 fusion-positive alveolar subtype. Here, we demonstrate that the expression levels of the transcriptional repressor TRPS1 are specifically enhanced in the embryonal subtype, resulting in impaired terminal myogenic differentiation and tumor growth. During normal myogenesis, expression levels of TRPS1 have to decrease to allow myogenic progression, as demonstrated by overexpression of TRPS1 in myoblasts impairing myotube formation. Consequentially, myogenic differentiation in embryonal rhabdomyosarcoma in vitro as well as in vivo can be achieved by reducing TRPS1 levels. Furthermore, we show that TRPS1 levels in RD cells, the bona fide model cell line for embryonal rhabdomyosarcoma, are regulated by miR-1 and that TRPS1 and MYOD1 share common genomic binding sites. The myogenin (MYOG) promoter is one of the critical targets of TRPS1 and MYOD1; we demonstrate that TRPS1 restricts MYOG expression and thereby inhibits terminal myogenic differentiation. Therefore, reduction of TRPS1 levels in embryonal rhabdomyosarcoma might be a therapeutic approach to drive embryonal rhabdomyosarcoma cells into myogenic differentiation, thereby generating postmitotic myotubes

TRPS1 shapes YAP/TEAD-dependent transcription in breast cancer cells

YAP is a transcriptional co-activator downstream of Hippo pathway that displays oncogenic but also tumour suppressive functions. Here, the authors perform an unbiased genome wide CRISPR screen and identify Trichorhinophalangeal syndrome 1 (TRPS1) that represses YAP/TEAD activity independently of Hippo pathway in breast cancer

Stat5 phosphorylation is reduced in <i>Miz1</i>Δ<i>POZ</i> mammary glands and in <i>shMiz1</i> HC11 cells.

<p>(<b>A</b>) Analysis of Stat5a/b mRNA expression in <i>Miz1</i>Δ<i>POZ</i> (ΔPOZ) and control mammary gland tissue (<i>Ctr</i>). (<b>B</b>) Immunoblot analysis of Stat5 in wildtype and <i>Miz1</i>Δ<i>POZ</i> mammary glands. (<b>C</b>) Immunohistochemical staining of pStat5 in the mammary gland tissue from wildtype and <i>Miz1</i>Δ<i>POZ</i> animals. (<b>D</b>) Western blots from HC11 cells stably transfected with a scrambled short hairpin (sh) RNA (shscr) or a Miz1 shRNA (see also Fig. 4<b>E</b> and <b>F</b>). Numbers indicated are fold changes of band intensities obtained by densitometry (see Materials and Methods). Quantitative RT-PCR for the prolactin receptor (<b>E</b>; <i>Prlr</i>), the Supressors of cytokine signalling (<i>Socs</i>) 1, 2 and 3 and caveolin-1 (<b>F</b>; <i>Cav1</i>), and for <i>ErbB4</i> (<b>G</b>). Lactation day 6 samples were used in all <i>in vivo</i> experiments. Scale bar in C: 50 µm.</p

Genes related to vesicular transport processes are bound by Miz1 and down-regulated in <i>Miz1</i>Δ<i>POZ</i> mammary glands.

<p>(<b>A</b>) GSEA analysis comparing the gene expression of wildtype versus <i>Miz1</i>Δ<i>POZ</i> mammary glands. The 100 Miz1 target promoters with the highest tag number were used as the gene set in this analysis. (<b>B</b>) Browser pictures of Miz1 ChIP-Seq profiles at the Miz1 target genes <i>Exoc2</i>, <i>Vamp4</i> and <i>Lrp12.</i> (<b>C</b>) Quantitative RT-PCRs testing the expression of genes indicated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0089187#pone-0089187-t001" target="_blank">Table 1</a>. (<b>D</b>) Electron microscopy showing vesicles with (arrows) and without (asterisks) casein micelles in tissue from control and <i>Miz1</i>Δ<i>POZ</i> animals. (<b>E</b>) Percentage of the two vacuole types in mammary gland epithelial cells of control and <i>Miz1</i>Δ<i>POZ</i> animals from lactation day 10. Data obtained from 4 animals per genotype. Total number of vacuoles counted: ctr, 309–379; ΔPOZ, 339–404. Scale bar in D: 1 µm.</p