title: Oncogenic STRAP functions as a novel negative regulator of E-cadherin and p21(Cip1) by modulating the transcription factor Sp1.
abstract: We have previously reported the identification of a novel WD-domain protein, STRAP that plays a role in maintenance of mesenchymal morphology by regulating E-cadherin and that enhances tumorigenicity partly by downregulating CDK inhibitor p21(Cip1). However, the functional mechanism of regulation of E-cadherin and p21(Cip1) by STRAP is unknown. Here, we have employed STRAP knock out and knockdown cell models (mouse embryonic fibroblast, human cancer cell lines) to show how STRAP downregulates E-cadherin and p21(Cip1) by abrogating the binding of Sp1 to its consensus binding sites. Moreover, ChIP assays suggest that STRAP recruits HDAC1 to Sp1 binding sites in p21(Cip1) promoter. Interestingly, loss of STRAP can stabilize Sp1 by repressing its ubiquitination in G1 phase, resulting in an enhanced expression of p21(Cip1) by >4.5-fold and cell cycle arrest. Using Bioinformatics and Microarray analyses, we have observed that 87% mouse genes downregulated by STRAP have conserved Sp1 binding sites. In NSCLC, the expression levels of STRAP inversely correlated with that of Sp1 (60%). These results suggest a novel mechanism of regulation of E-cadherin and p21(Cip1) by STRAP by modulating Sp1-dependent transcription, and higher expression of STRAP in lung cancer may contribute to downregulation of E-cadherin and p21(Cip1) and to tumor progression.
authors.affiliation: a Division of Hematology and Oncology; Department of Medicine; UAB Comprehensive Cancer Center; University of Alabama at Birmingham ; Birmingham , AL USA.
authors.forename: Lin
authors.initials: L
authors.lastname: Jin
authors.forename: Pran K
authors.initials: PK
authors.lastname: Datta
mesh_terms: D000818:Animals; D001665:Binding Sites; D015820:Cadherins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D059447:Cell Cycle Checkpoints; D002460:Cell Line; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation; D016193:G1 Phase; D057809:HEK293 Cells; D006367:HeLa Cells; D056284:Histone Deacetylase 1 / Q000378:metabolism; D006801:Humans; D051379:Mice; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D016329:Sp1 Transcription Factor / Q000737:chemistry / Q000378:metabolism*; D015533:Transcriptional Activation; D054875:Ubiquitination
chemical_list: D015820:Cadherins; D002352:Carrier Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D012333:RNA, Messenger; D016329:Sp1 Transcription Factor; C434146:Strap protein; C110550:HDAC1 protein, human; D056284:Histone Deacetylase 1
keywords: CDK2, cyclin-dependent kinase 2; CDK4, cyclin-dependent kinase 4; HDAC1, histone deacetylase 1; HDAC2, histone deacetylase 2; HDAC3, histone deacetylase 3; HNF4, hepatocyte nuclear factor 4; MEF, mouse embryonic fibroblast; NF-YA, nuclear transcription factor Y subunit alpha; PARP, poly (ADP-ribose) polymerase; RNase, A ribonuclease A; RhoA, Ras homolog gene family, member A; STRAP; STRAP, serine threonine kinase receptor-associated protein; SWI/SNF, SWItch/Sucrose nonfermentable; Sp/KLF, specificity protein/Krüppel-like factor; Sp1; Sp1, specificity protein 1; TSA, trichostatin A; TSS, transcription start site; TβR I, II, TGF-β receptor I, II; cell cycle; p300/CBP, p300/ CREB-binding protein; transcription factor; ubiquitination