In particular, the lysine residues K369 and K374 in SPZ1 were found to be critical for tumor growth, and this was confirmed using the AC mutant of SPZ1 (Fig
In particular, the lysine residues K369 and K374 in SPZ1 were found to be critical for tumor growth, and this was confirmed using the AC mutant of SPZ1 (Fig. of SPZ1 at positions 369 and 374, and of TWIST1 at positions 73 and 76, which are required for SPZ1CTWIST1 PSEN1 complex formation and cancer cell migration in vitro and in vivo. Ectopic SPZ1 and TWIST1 expression, but not that of TWIST1 alone, enhanced vascular endothelial growth factor (VEGF) expression via the recruitment of bromodomain-containing protein 4 (BRD4), thus enhancing RNA-Pol II-dependent transcription and inducing metastasis. Neutralization of VEGF using humanized monoclonal antibodies such as Avastin, effectively abrogated the EMT and oncogenesis induced by the acetylated SPZ1CTWIST1 complex. Our findings highlight the importance of acetylation signaling in the SPZ1CTWIST1CBRD4 axis in the mediation of EMT and its regulation during tumor initiation and metastasis.  and is known as a major inducer of EMT in human mammary epithelial cells  and other cancers such as sarcoma, melanoma, and lymphoma [4, 5]. Increased TWIST1 expression promotes EMT by regulating cell motility and invasive activity and enhances some features of cancer stem cells through control of downstream gene expression [5, 6]. One unique function of TWIST1 is that it represses the transcription of the E-cadherin promoter via expression . Despite the potential oncogenic activity of SPZ1, the detailed regulatory mechanisms of SPZ1 remain unclear. We show here that (1) TIP60 acetylates SPZ1 and TWIST1, (2) acetylated SPZ1 interacts with acetylated TWST1, and (3) this complex recruits the bromodomain-containing protein 4 (BRD4) to enhance RNA polymerase II (Pol II) transcription , thereby promoting angiogenesis and metastasis in vitro and in vivo. Therefore, SPZ1 is an important regulator of tumor metastasis and cell plasticity in the tumorigenic microenvironment. Results SPZ1 directly interacts with TWIST1 in vitro and in vivo EpithelialCmesenchymal transition (EMT) has been proposed as a key step in tumor progression and metastasis. The hallmark of EMT is loss of epithelial marker expression (E-cadherin Echinomycin and catenin) and gain of mesenchymal markers (N-cadherin, Vimentin, and SMS-actin). TWIST1 has been implicated in tumor initiation, stemness, angiogenesis, dissemination, and chemoresistance in various carcinomas, sarcomas, and hematological malignancies . However, the precise targets of, or molecules associated with, TWIST1 have not been well characterized, with the exception of MEF2 , TCF3, p300/PCAF , and its interaction with BRD4 . To elucidate the potential regulatory mechanisms of TWIST1 signaling in tumorigenesis and metastasis, co-immunoprecipitation coupled with two-dimensional gel electrophoresis (2-DE) and liquid chromatographyCmass spectrometry was conducted to identify TWIST1-interacting proteins in lysates of the aggressive hepatoma cell line SK-Hep1 (Fig. ?(Fig.1a).1a). This approach yielded six candidate proteins from three independent 2-DE experiments (Supplementary Figure S1a). The oligopeptides GLDKINEMLSTNLPVSLAPEKEDNEK (amino acids 115?140) and SQKDISETCGNNGVGFQTQPNNEVSAK (amino acids 226?252) were detected via liquid chromatographyCmass spectrometry, sequenced, and their origin identified as SPZ1 (gi 21707289) (Fig. ?(Fig.1a,1a, Supplementary Fig. S1a, and S1b). The expression levels of SPZ1 were previously shown to be higher in the aggressive hepatoma cell lines SK-Hep1 and HA 22T than in HepG2 and Huh 7 hepatoma cells, while the Alexander hepatoma cell line PLC5, Hep 3B, and benign hepatocytes (Chang liver CNL) had lower or undetectable expression of this protein . Open in a separate window Fig. 1 SPZ1 interacts with TWIST1 in vitro and in vivo. a The SPZ1 protein was detected in anti-TWIST1 immunoprecipitates. The SPZ1 protein (No. 358 in Fig. S1a) obtained from anti-TWIST1 immunoprecipitates of SK-Hep1 cell lysates was identified by liquid chromatography?tandem mass spectrometry (LC-MS-MS). b SPZ1-GFP associates with FLAG-TWIST1 and its interaction with other proteins (TIP60, BRD4, and Pol II) in SK-Hep1 Echinomycin and HA Echinomycin 22T cells, as assayed by Echinomycin immunoprecipitation (IP) and western blotting. c SPZ1-YFP colocalized with TWIST1-CFP in SK-Hep1 cells, as determined by fluorescence resonance energy transfer (FRET) assay. Green, YFP; cyan, CFP; FRET signals (lower panels). The oblique line indicates the analyzing sites for FRET. The red and yellow arrows indicate cytosol and nuclei, respectively. d SPZ1 interacts with TWIST1 in liver tumors from transgenic mice, TG1 and TG2. L: light chain; arrowhead, TWIST1. e SPZ1 interacts with TWIST1 in tumor tissues derived from.