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Human ortholog of Drosophila Melted impedes SMAD2 release from TGF-β receptor I to inhibit TGF-β signaling

  1. Theodore J. Browna,b,c,1
  1. aLunenfeld-Tanenbaum Research Institute at Mount Sinai Hospital, Toronto, ON, Canada M5T 3H7;
  2. Departments of bPhysiology,
  3. cObstetrics and Gynaecology,
  4. dCell and Systems Biology, and
  5. fMolecular Genetics, University of Toronto, Toronto, ON, Canada M5S 3G5;
  6. ePrincess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada M5G 1L7

  1. Edited by Igor B. Dawid, The Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, and approved May 5, 2015 (received for review March 11, 2015)

Significance

Ventricular zone expressed pleckstrin homology domain-containing 1 (VEPH1) is among genes on chromosome 3q24-26, a region amplified in several cancers. Although little is known of mammalian VEPH1, its Drosophila ortholog, Melted, is involved in neural and eye development, metabolism, and size determination through effects on Forkhead box O, target of rapamycin, and Hippo signaling. We show that VEPH1 expression affects similar gene categories as Melted and potently inhibits transforming growth factor-β (TGF-β) signaling. VEPH1 interacts with TGF-β type I receptor (TβRI) and inhibits dissociation of activated Sma- and Mad-related protein 2 from TβRI, resulting in impaired TGF-β signaling. TGF-β acts initially as a tumor suppressor through its cytostatic activity, but subsequently promotes tumor progression. These findings suggest that VEPH1 could affect TGF-β activity during cancer development/progression.

Abstract

Drosophila melted encodes a pleckstrin homology (PH) domain-containing protein that enables normal tissue growth, metabolism, and photoreceptor differentiation by modulating Forkhead box O (FOXO), target of rapamycin, and Hippo signaling pathways. Ventricular zone expressed PH domain-containing 1 (VEPH1) is the mammalian ortholog of melted, and although it exhibits tissue-restricted expression during mouse development and is potentially amplified in several human cancers, little is known of its function. Here we explore the impact of VEPH1 expression in ovarian cancer cells by gene-expression profiling. In cells with elevated VEPH1 expression, transcriptional programs associated with metabolism and FOXO and Hippo signaling were affected, analogous to what has been reported for Melted. We also observed altered regulation of multiple transforming growth factor-β (TGF-β) target genes. Global profiling revealed that elevated VEPH1 expression suppressed TGF-β–induced transcriptional responses. This inhibitory effect was verified on selected TGF-β target genes and by reporter gene assays in multiple cell lines. We further demonstrated that VEPH1 interacts with TGF-β receptor I (TβRI) and inhibits nuclear accumulation of activated Sma- and Mad-related protein 2 (SMAD2). We identified two TβRI-interacting regions (TIRs) with opposing effects on TGF-β signaling. TIR1, located at the N terminus, inhibits canonical TGF-β signaling and promotes SMAD2 retention at TβRI, similar to full-length VEPH1. In contrast, TIR2, located at the C-terminal region encompassing the PH domain, decreases SMAD2 retention at TβRI and enhances TGF-β signaling. Our studies indicate that VEPH1 inhibits TGF-β signaling by impeding the release of activated SMAD2 from TβRI and may modulate TGF-β signaling during development and cancer initiation or progression.

Footnotes

  • ↵1To whom correspondence should be addressed. Email: brown{at}lunenfeld.ca.

  • Author contributions: P.S., A.K., M.J.R., J.L.W., and T.J.B. designed research; P.S. and A.K. performed research; P.S., J.L.W., and T.J.B. contributed new reagents/analytic tools; P.S., A.K., C.V., and T.J.B. analyzed data; and P.S., A.K., M.J.R., J.L.W., and T.J.B. wrote the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission.

  • Data deposition: The microarray data reported in this paper have been deposited in the Gene Expression Omnibus (GEO) database, www.ncbi.nlm.nih.gov/geo (accession no. GSE67765).

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1504671112/-/DCSupplemental.

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