Oncogene database

7291

TWIST1

twist family bHLH transcription factor 1;TWIST1;twist family bHLH transcription factor 1

B-HLH DNA binding protein|H-twist|TWIST homolog of drosophila|class A basic helix-loop-helix protein 38|twist basic helix-loop-helix transcription factor 1|twist homolog 1|twist-related protein 1

7p21.2

protein-coding

Oncogene activation increases susceptibility to apoptosis. Thus, tumorigenesis must depend, in part, on compensating mutations that protect from programmed cell death. A functional screen for cDNAs that could counteract the proapoptotic effects of the myc oncogene identified two related bHLH family members, Twist and Dermo1. Both of these proteins inhibited oncogene- and p53-dependent cell death. Twist expression bypassed p53-induced growth arrest. These effects correlated with an ability of Twist to interfere with activation of a p53-dependent reporter and to impair induction of p53 target genes in response to DNA damage. An underlying explanation for this observation may be provided by the ability of Twist to reduce expression of the ARF tumor suppressor. Thus, Twist may affect p53 indirectly through modulation of the ARF/MDM2/p53 pathway. Consistent with a role as a potential oncoprotein, Twist expression promoted colony formation of E1A/ras-transformed mouse embryo fibroblasts (MEFs) in soft agar. Furthermore, Twist was inappropriately expressed in 50% of rhabdomyosarcomas, a tumor that arises from skeletal muscle precursors that fail to differentiate. Twist is known to block myogenic differentiation. Thus, Twist may play multiple roles in the formation of rhabdomyosarcomas, halting terminal differentiation, inhibiting apoptosis, and interfering with the p53 tumor-suppressor pathway.

Despite evidence that Twist, a highly conserved basic helix-loop-helix transcription factor, is a novel oncogene, there are no reports describing Twist expression in pancreatic cancer. Intraductal papillary mucinous neoplasm (IPMN) and pancreatic intraepithelial neoplasia (PanIN) are precursor lesions of pancreatic cancer. To clarify involvement of Twist expression in pancreatic cancer, we used quantitative reverse transcription-polymerase chain reaction and examined Twist expression in pancreatic cancer, IPMN, and non-neoplastic pancreas using bulk tissues (11 cancers, 18 IPMNs, and 15 non-neoplastic pancreata), microdissected cells (cancer from 22 sections, IPMN from 19 sections, PanIN from 6 sections, and pancreatitis-affected epithelial cells from 14 sections), and pancreatic juice (16 from cancer, 28 from IPMN, and 17 from pancreatitis). Twist expression differed significantly between cancer and IPMN bulk tissues (p < 0.0001) but not between cancer and non-neoplastic tissues. Twist expressions differed significantly between microdissected cancer cells, IPMN cells, and pancreatitis-affected cells (all comparisons, p < 0.017). PanIN cells expressed significantly lower levels of Twist than did IDC cells (p = 0.016). Twist expression differed significantly between cancer and IPMN juice samples (p = 0.0002) but not between cancer and pancreatitis juice samples. Receiver operation characteristic curve analyses revealed that measurement of Twist was more useful for discriminating cancer from IPMN than from chronic pancreatitis (p = 0.009). Our results suggest that Twist is involved in tumor progression of pancreatic cancer and that measurement of Twist in pancreatic juice may be useful to differentiate pancreatic cancer from nonmalignant neoplasms such as IPMN.

Hypoxia-inducible factors (HIFs) are highly conserved transcription factors that play a crucial role in oxygen homeostasis. Intratumoral hypoxia and genetic alterations lead to HIF activity, which is a hallmark of solid cancer and is associated with poor clinical outcome. HIF activity is regulated by an evolutionary conserved mechanism involving oxygen-dependent HIFalpha protein degradation. To identify novel components of the HIF pathway, we performed a genome-wide RNA interference screen in Caenorhabditis elegans, to suppress HIF-dependent phenotypes, like egg-laying defects and hypoxia survival. In addition to hif-1 (HIFalpha) and aha-1 (HIFbeta), we identified hlh-8, gska-3 and spe-8. The hlh-8 gene is homologous to the human oncogene TWIST1. We show that TWIST1 expression in human cancer cells is enhanced by hypoxia in a HIF-2alpha-dependent manner. Furthermore, intronic hypoxia response elements of TWIST1 are regulated by HIF-2alpha, but not HIF-1alpha. These results identify TWIST1 as a direct target gene of HIF-2alpha, which may provide insight into the acquired metastatic capacity of hypoxic tumors.

Mammalian Twist1, a master regulator in development and a key factor in tumorigenesis, is known to repress transcription by several mechanisms and is therefore considered to mediate its function mainly through inhibition. A role of Twist1 as transactivator has also been reported but, so far, without providing a mechanism for such an activity. Here we show that heterodimeric complexes of Twist1 and E12 mediate E-box-dependent transcriptional activation. We identify a novel Twist1 transactivation domain that coactivates together with the less potent E12 transactivation domain. We found three specific residues in the highly conserved WR domain to be essential for the transactivating function of murine Twist1 and suggest an alpha-helical structure of the transactivation domain.

PURPOSE: Transcription factor Twist1 is known to play a vital role in cancer development, progression and metastasis. However, regulation mechanisms beneath Twist1 expression, as well as the correlation between its expression and bladder urothelial carcinoma (BUC), are still under investigation. Herein, we tried to investigate the expression of Twist1 in BUC specimens and non-cancerous mucosas and illustrate their relationships with clinicopathological features. METHODS: The expression of Twist1 mRNA in 42 fresh BUC specimens and 13 paired non-cancerous mucosas was detected by real-time fluorescence quantitative reverse transcription polymerase chain reaction (RFQ-RTPCR). Immunohistochemistry (IHC) was used to detect the expression of Twist1 protein in 40 paraffin embedded BUC specimens and 14 paired non-cancerous mucosas, and their relationships with clinicopathological features. RESULTS: The expression levels of Twist1 mRNA in 13 paired BUC specimens were significantly lower than the non-cancerous mucosas. The positive expression rate of Twist1 protein in BUC specimens (90.0%; 36/40) was significantly higher than the non-cancerous mucosas (7.14%; 1/14). Twist1 protein was mainly distributed in the nucleus, and expressed obviously in the mesenchymal cells of several specimens (13.9%;5/36). However, expressions of Twist1 protein were not associated with TNM stage and grade. It was also shown that the expression tendency of Twist1 protein was distinct from Twist1 mRNA, and both were not correlated with age, gender, and smoking history. CONCLUSION: As a probable potential biomarker for BUC, Twist1 gene may play a role as an oncogene during the tumorigenesis and development of BUC. Its abnormal protein expression may be associated with disordered regulations after transcription.

Upregulation of the proto-oncogene Twist1 is highly correlated with acquired drug resistance and poor prognosis in human cancers. Altered expression of this multifunctional transcription factor is also associated with inherited skeletal malformations. The mammalian Twist1 3 UTRs are highly conserved and contain a number of potential regulatory elements including miRNA target sites. We analyzed the translational regulation of TWIST1 using luciferase reporter assays in a variety of cell lines. Among several miRNAs tested, miR-145a-5p, miR-151-5p and a combination of miR-145a-5p + miR-151-5p and miR-151-5p + miR-337-3p were able to significantly repress Twist1 translation. This phenomena was confirmed with both exogenous and endogenous miRNAs and was dependent on the presence of the predicted target sites in the 3 UTR. Furthermore, the repression was sensitive to LNA-modified miRNA antagonists and resulted in decreased migratory potential of murine embryonic fibroblast cells. Understanding the in vivo mechanisms of this oncogene s regulation might open up a possibility for therapeutic interference by gene specific cancer therapies.