McCartney, B. M., Kulikauskas, R. M., LaJeunesse, D. R. & Fehon, R. G. The neurofibromatosis-2 homologue, Merlin, and the tumor suppressor expanded function together in Drosophila to regulate cell proliferation and differentiation. Development 127, 1315-1324

Developmental, Cell and Molecular Biology Group, Duke University, Durham, NC 27708-1000, USA.
Development (Impact Factor: 6.46). 04/2000; 127(6):1315-24.
Source: PubMed


Neurofibromatosis-2 is an inherited disorder characterized by the development of benign schwannomas and other Schwann-cell-derived tumors associated with the central nervous system. The Neurofibromatosis-2 tumor suppressor gene encodes Merlin, a member of the Protein 4.1 superfamily most closely related to Ezrin, Radixin and Moesin. This discovery suggested a novel function for Protein 4.1 family members in the regulation of cell proliferation; proteins in this family were previously thought to function primarily to link transmembrane proteins to underlying cortical actin. To understand the basic cellular functions of Merlin, we are investigating a Drosophila Neurofibromatosis-2 homologue, Merlin. Loss of Merlin function in Drosophila results in hyperplasia of the affected tissue without significant disruptions in differentiation. Similar phenotypes have been observed for mutations in another Protein 4.1 superfamily member in Drosophila, expanded. Because of the phenotypic and structural similarities between Merlin and expanded, we asked whether Merlin and Expanded function together to regulate cell proliferation. In this study, we demonstrate that recessive loss of function of either Merlin or expanded can dominantly enhance the phenotypes associated with mutations in the other. Consistent with this genetic interaction, we determined that Merlin and Expanded colocalize in Drosophila tissues and cells, and physically interact through a conserved N-terminal region of Expanded, characteristic of the Protein 4.1 family, and the C-terminal domain of Merlin. Loss of function of both Merlin and expanded in clones revealed that these proteins function to regulate differentiation in addition to proliferation in Drosophila. Further genetic analyses suggest a role for Merlin and Expanded specifically in Decapentaplegic-mediated differentiation events. These results indicate that Merlin and Expanded function together to regulate proliferation and differentiation, and have implications for understanding the functions of other Protein 4.1 superfamily members.

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Available from: Dennis Lajeunesse, Mar 30, 2015
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    • "Merlin also modulates the activity of non-receptor Thr/Ser kinases such as PAK1/2 [23]. Additionally, merlin regulates cell proliferation and differentiation [24], and functions upstream of the Hippo signaling pathway [15], [25], [26], [27], [28]. However, it remains unclear as to how merlin exerts its tumor suppressor function in mammalian cells and how it contributes to cancer growth and progression. "
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    ABSTRACT: Merlin is encoded by the neurofibromatosis type 2 (NF2) gene and is a member of the Band 4.1 protein family. This protein acts as a linker that connects cell surface proteins to the actin cytoskeleton. Defects caused by mutations of the NF2 gene give rise to NF2 disease, which is generally characterized by the formation of bilateral vestibular schwannomas and, to a lesser extent, meningiomas and ependymomas. In addition to these tumor types, NF2 is mutated and/or merlin expression is reduced or lost in numerous non-NF2 associated tumors, including melanoma. However, the role of merlin in human melanoma growth and the mechanism underlying its effect are currently unknown. In the present study, we show that merlin knockdown enhances melanoma cell proliferation, migration, and invasion in vitro and that decreased merlin expression promotes subcutaneous melanoma growth in immunocompromised mice. Concordantly, we find that increased expression of merlin in a metastatic melanoma cell line reduced their in vitro migration and proliferation, and diminished their ability to grow in an anchorage independent manner. Increased merlin expression also inhibits in vivo growth of these melanoma cells. Lastly, we demonstrate that higher merlin levels in human melanoma cells promote the H(2)O(2)-induced activation of MST1/2 Ser/Thr kinases, which are known tumor suppressors in the Hippo signaling pathway. Taken together, these results provide for the first time evidence that merlin negatively regulates human melanoma growth, and that loss of merlin, or impaired merlin function, results in an opposite effect. In addition, we show that increased merlin expression leads to enhanced activation of the MTS1/2 kinases, implying the potential roles of MST1/2 in mediating the anti-melanoma effects of merlin.
    Preview · Article · Aug 2012 · PLoS ONE
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    • "A mutated expanded (ex) gene was originally identified in 1926 and shown to enhance the growth of imaginal discs in Drosophila, suggesting that ex functions as a tumor suppressor (Stern and Bridges, 1926). Since then, ex has been definitely classified as a tumor suppressor due to its abilities to restrict growth, differentiation and enhance apoptosis in the wings and eyes of flies (Boedigheimer and Laughon, 1993; Blaumueller and Mlodzik, 2000; McCartney et al., 2000). Due to the similar overgrowth phenotypes seen in the imaginal discs of flies exhibiting mutations in the core Hippo pathway components, ex was added as a key player in this pathway (Hamaratoglu et al., 2006). "
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    ABSTRACT: The Hippo signaling network is proving to be an essential regulator within the cell, participating in multiple cellular phenotypes including cell proliferation, apoptosis, cell migration and organ size control. Much of this pathway is conserved from flies to mammals; however, how the upstream components, namely Expanded, affect downstream processes in mammalian systems has remained elusive. Only recently has human Expanded (hEx), also known as FRMD6 or Willin, been identified. However, its functional significance with respect to its putative tumor suppressor function and activation of the Hippo pathway has not been studied. In this study, we show for the first time that hEx possesses several tumor suppressor properties. First, hEx dramatically inhibits cell proliferation in two human cancer cell lines, MDA-MB-231 and MDA-MB-436 cells, and sensitizes these cells to the chemotherapeutic drug Taxol. Furthermore, downregulation of hEx in the immortalized MCF10A breast cell line leads to enhanced proliferation and resistance to Taxol treatment. As evidence for its tumor suppressor function, overexpression of hEx inhibits colony formation, soft agar colony growth in vitro and in vivo tumor growth in nude mice. Although Drosophila expanded (ex) can activate the Hippo pathway, surprisingly no significant alterations were discovered in the phosphorylation status of any of the Hippo pathway components, including downstream tumor suppressor LATS1, upon overexpression of hEx. In addition, knockdown of both LATS1 and LATS2 in hEx-overexpressing cells was unable to rescue the hEx phenotype, suggesting that hEx functions independently of the Hippo pathway in this cell line. Alternatively, we propose a mechanism through which hEx inhibits progression through the S phase of the cell cycle by upregulating p21(Cip1) and downregulating Cyclin A. This is the first study to functionally characterize hEx and show that hEx acts in a distinct manner compared with Drosophila expanded.
    Full-text · Article · Jul 2011 · Oncogene
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    • "Most identified target genes of Yki, such as cyclin E, Myc, diap, and bantam, promote cell proliferation or cell survival (Goulev et al., 2008; Wu et al., 2008; Zhang et al., 2008; Zhao et al., 2008; Ziosi et al., 2010). For the upstream regulators, Merlin (Mer) and Expanded (Ex), two FERM domain-containing family proteins, as well as the WW and C2 domain-containing protein Kibra, interact with the Hippo kinase cascade and activate Wts (Baumgartner et al., 2010; Genevet et al., 2010; Hamaratoglu et al., 2006; McCartney et al., 2000; Yu et al., 2010). Mediators of the planar cell polarity, such as the atypical cadherin Fat (Ft) and the unconventional myosin Dachs, also influence the Hippo pathway (Bennett and Harvey, 2006; Cho et al., 2006; Silva et al., 2006; Tyler and Baker, 2007; Willecke et al., 2006, 2008; Zecca and Struhl, 2010). "
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    ABSTRACT: During Drosophila oogenesis, the somatic follicle cells form an epithelial layer surrounding the germline cells to form egg chambers. In this process, follicle cell precursors are specified into polar cells, stalk cells, and main-body follicle cells. Proper specification of these three cell types ensures correct egg chamber formation and polarization of the anterior-posterior axis of the germline cells. Multiple signaling cascades coordinate to control the follicle cell fate determination, including Notch, JAK/STAT, and Hedgehog signaling pathways. Here, we show that the Hippo pathway also participates in polar cell specification. Over-activation of yorkie (yki) leads to egg chamber fusion, possibly through attenuation of polar cell specification. Loss-of-function experiments using RNAi knockdown or generation of mutant clones by mitotic recombination demonstrates that reduction of yki expression promotes polar cell formation in a cell-autonomous manner. Consistently, polar cells mutant for hippo (hpo) or warts (wts) are not properly specified, leading to egg chamber fusion. Furthermore, Notch activity is increased in yki mutant cells and reduction of Notch activity suppresses polar cell formation in yki mutant clones. These results demonstrate that yki represses polar cell fate through Notch signaling. Collectively, our data reveal that the Hippo pathway controls polar cell specification. Through repressing Notch activity, Yki serves as a key repressor in specifying polar cells during Drosophila oogenesis.
    Preview · Article · Jul 2011 · Developmental Biology
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