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Human homolog of Drosophila expanded, hEx, functions as a putative tumor suppressor in human cancer cell lines independently of the Hippo pathway

Oncogene volume 31, pages 1189–1195 (2012)Cite this article

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 p21Cip1 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.

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Acknowledgements

This work was supported by a grant from the Canadian Institute of Health Research, a New Investigator Award from the Canadian Institute of Health Research and an Early Researcher Award from the Ontario Ministry of Research and Innovation, Canada, to Xiaolong Yang; and an Ontario Graduate Scholarship to Stacy Visser-Grieve. We would like to thank Matt Gordon at the Queen's Cancer Research Institute for performing the FACS analysis and Dr Frank Gunn-Moore for providing the hEx-GFP plasmid.

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  1. Department of Pathology and Molecular Medicine, Queen's University, Kingston, Ontario, Canada

    S Visser-Grieve, Y Hao & X Yang

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  1. S Visser-Grieve
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Correspondence to X Yang.

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Visser-Grieve, S., Hao, Y. & Yang, X. Human homolog of Drosophila expanded, hEx, functions as a putative tumor suppressor in human cancer cell lines independently of the Hippo pathway. Oncogene 31, 1189–1195 (2012). https://doi.org/10.1038/onc.2011.318

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