Normal and disease-related biological functions of Twist1 and underlying molecular mechanisms

Abstract

This article reviews the molecular structure, expression pattern, physiological function, pathological roles and molecular mechanisms of Twist1 in development, genetic disease and cancer. Twist1 is a basic helix-loop-helix domain-containing transcription factor. It forms homo- or hetero-dimers in order to bind the Nde1 E-box element and activate or repress its target genes. During development, Twist1 is essential for mesoderm specification and differentiation. Heterozygous loss-of-function mutations of the human Twist1 gene cause several diseases including the Saethre-Chotzen syndrome. The Twist1-null mouse embryos die with unclosed cranial neural tubes and defective head mesenchyme, somites and limb buds. Twist1 is expressed in breast, liver, prostate, gastric and other types of cancers, and its expression is usually associated with invasive and metastatic cancer phenotypes. In cancer cells, Twist1 is upregulated by multiple factors including SRC-1, STAT3, MSX2, HIF-1α, integrin-linked kinase and NF-κB. Twist1 significantly enhances epithelial-mesenchymal transition (EMT) and cancer cell migration and invasion, hence promoting cancer metastasis. Twist1 promotes EMT in part by directly repressing E-cadherin expression by recruiting the nucleosome remodeling and deacetylase complex for gene repression and by upregulating Bmi1, AKT2, YB-1, etc. Emerging evidence also suggests that Twist1 plays a role in expansion and chemotherapeutic resistance of cancer stem cells. Further understanding of the mechanisms by which Twist1 promotes metastasis and identification of Twist1 functional modulators may hold promise for developing new strategies to inhibit EMT and cancer metastasis.

Figure 1

Comparison of amino-acid sequences among human (H), mouse (M), Xenopus (X), Drosophila (D), leech (L) and C. elegans (C) Twist1. The Twist1 amino-acid sequences from human (NP_000465.1), mouse (NP_035788.1), Xenopus (NP_001079352.1), Drosophila (NP_523816.2), leech (AAL05567.1) and C. elegans (AAC26105.1) have been aligned with the aid of the computer program Clustal W2 (Larkin et al., 2007). “^*” indicates the identical residues in all sequences in the alignment; “#” indicates conserved substitutions; “$” indicates semi-conserved substitutions; “-” indicates gaps in the alignment.

Figure 2

Molecular structure of the human Twist1 protein. The number of amino-acid residues for each structural domain is indicated. The regions that interact with other proteins are also indicated by solid lines. NLS1 and NLS2, nuclear localization signal sequences 1 and 2; bHLH, basic helix-loop-helix domain; WR, the tryptophan and arginine motif; CBP, cAMP-response element binding protein (CREB)-binding protein; PCAF, p300/CBP-associated factor, Runx2, Runt-related transcription factor; E12/E47, a bHLH transcription factor that forms dimer with Twist1; MyoD, a bHLH transcription factor that regulates muscle differentiation.

Figure 3

Twist1 recruits Mi-2/NuRD complex to repress E-cadherin expression and promote EMT and metastasis. Twist1 forms heterodimer with E12, and interacts with the components of MTA2 (metastasis-associated protein 2), RbAp46 (Rb-associated protein 46) and Mi-2 in the Mi-2/NuRD protein complex. Consequently, the Mi-2/NuRD complex is recruited to the E-cadherin promoter by Twist1, resulting in suppression of E-cadherin expression and promotion of EMT and metastasis of breast cancer. Knockdown of Twist, MTA2 or RbAp46 in the complex inhibits breast cancer cell metastasis.

Figure 4

Possible regulatory pathways by which Twist1 is involved in cancer progression. Factors that directly or indirectly upregulate Twist1 are listed on the left side. Targets and cellular functions that are directly or indirectly regulated by Twist1 are listed on the right side. SRC-1, steroid receptor coactivator-1; STAT3, signaling transducer and activator of transcription 3; MSX2, Msh homeobox 2; HIF-1α, hypoxia-inducible factor 1α NF-κB, nuclear factor kappa B; LMP1, EBV latent membrane protein 1; ILK, integrin-linked kinase; IFN, type I interferon; Axl, Axl receptor tyrosine kinase; miR-10b, micro-RNA 10b; Wnt, wingless and Int; Tcf4, transcription factor 4; Mi-2/NuRD, nucleosome remodeling and deacetylase protein complex; YB-1, Y-box binding protein-1; TIMP1, tissue inhibitor of metalloproteinase-1; VEGF, vascular endothelial growth factor; DKK-1, dickkopt-related protein 1; RhoC, ras homolog C; MMP2, metalloproteinase 2; CXCR4, chemokine (C-X-C motif) receptor 4; CCR7, chemokine (C-C motif) receptor 7; CD29, integrin β1; CD44, CD44 antigen; CD54, inter-cellular adhesion molecule 1; Bmi1, BMI1 polycomb ring finger oncogene; HER2, human epidermal growth factor receptor 2; TNFα, tumor necrosis factor α EMT, epithelial-mesenchymal transition.