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

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.

The Hippo pathway in colorectal cancer

“…Polymorphisms associated with Alzheimer's disease [117], CCL: downregulation leads to resistance to Taxol I MC10FA cells [118] Not studied…”

Framework for the Integration of Genomics, Epigenomics and Transcriptomics in Complex Diseases

“…2). Interestingly, rs401681 -TERT/CPTL1M , a variant strongly associated with low-grade and low-risk UBC [38] , was found to be associated with a lower expression of FRMD6 in our study, a gene that was reported to be involved in the inhibition of proliferation in human cells [39] .…”

14-3-3 Proteins interact with FRMD6 and regulate its subcellular localization in breast cancer cells

“…Overexpression of FRMD6 in MDA-MB-231 and MDA-MB-436 breast cancer cells suppresses cell proliferation and up-regulates their sensitivity to chemotherapeutic drug Taxol [20] . Therefore, we tested the anti-proliferative ability of the T28A mutant of FRMD6.…”

“…Knockdown of FRMD6 in MCF10A cells induces Epithelial-Mesenchymal transition (EMT) [19] . Overexpression of FRMD6 in MDA-MB-231 and MDA-MB-436 breast cancer cells suppresses cell proliferation and upregulates their sensitivity to chemotherapeutic drug Taxol [20] . Although we have already known that FRMD6 functions as a tumor suppressor via the Hippo pathway, the regulatory mechanism on FRMD6 still remains elusive.…”