HOXA5-Twist Interaction Alters p53 Homeostasis in Breast Cancer Cells

Abstract

The homeotic gene HOXA5 has been shown to play an important role in breast tumorigenesis. We have shown that loss of p53 correlated with loss of a developmentally regulated transcription factor, HOXA5, in primary breast cancer. Searching for potential protein interacting partners we found that HOXA5 binds to an antiapoptotic protein, Twist. Furthermore, Twist-overexpressing MCF-7 cells displayed a deregulated p53 response to ␥-radiation and decreased regulation of downstream target genes. Using a p53-promoter-reporter system, we demonstrated that HOXA5 could partially restore the inhibitory effects of Twist on p53 target genes. These effects are likely mediated through both the transcriptional up-regulation of p53 and the protein-protein interaction between HOXA5 and Twist. Thus, the loss of HOXA5 expression could lead to the functional activation of Twist resulting in aberrant cell cycle regulation and promoting breast carcinogenesis.The HOX 1 family of homeobox-containing genes encodes transcription factors that are highly conserved from Drosophila to Homo sapiens (1, 2). Transcription factors encoded by the HOX genes are essential for maintaining the positional identity of cells along the major body axis. Activation of HOX genes establishes a developmental guide that remains conserved throughout development (1-3). Failure of the molecular systems that control development results in a prevention of normal embryo growth and disruptions in this control system have been shown to be involved in a wide variety of cancers (4 -7).Several studies have linked HOX function to neoplastic growth, where translocations involving HOX genes were shown to be the underlying cause of leukemias and lymphomas (8 -10). Selected HOX genes have been shown to be differentially expressed in neoplasms of the colon, lung, kidney, and breast, but their functional relationship to the neoplastic phenotype remains to be elucidated (11).We have shown that HOXA5 expression is higher in normal breast epithelium than in breast carcinomas (7). Seeking a functional role for HOXA5, we observed consensus HOX binding sites within the p53 promoter and showed that HOXA5 is a potent transactivator of the p53 promoter. In an effort to identify protein-protein interacting partners of HOXA5, we performed a yeast two-hybrid screen that identified Twist as an interacting partner.Twist was initially discovered as a gene required for the formation of mesodermal patterns in early Drosophila zygotic development (12, 13). The Twist protein belongs to the family of basic helix-loop-helix transcription factors that exert their activity as transactivating factors through dimer formation (14). Mutations in the Twist gene can give rise to Saethre-Chotzen syndrome, an autosomal dominant disease, which results in craniosynostosis (15-17). In addition, mutations in the helix domain of the Twist gene can cause subcellular mislocalization and increased degradation of its protein product (18), which results in the repression of pro-inflammatory cytokine gene expression (19)...

PKB/AKT phosphorylation of the transcription factor Twist-1 at Ser42 inhibits p53 activity in response to DNA damage

“…Therefore, it remains to be addressed whether the effect of Twist-1 Ser42 phosphorylation on p53 and the induction of its target genes are direct or mediated through other molecules. It was described previously that Twist-1 can inhibit a potent p53 transactivator homeobox protein HOXA5, compromising the p53 response to g-irradiation through suppressed induction of p21 Waf1 and inhibition of Ser20 phosphorylation (Stasinopoulos et al, 2005). Expression of Twist-1 decreases the level of the p53 upstream activator p14 ARF , presumably by affecting production of its mRNA (Kwok et al, 2007).…”

Twist and p53 reciprocally regulate target genes via direct interaction

“…Furthermore, it has been shown that Twist antagonizes p53 (Stasinopoulos et al, 2005). Various transcription factors and co-factors have been shown to have functional interactions with p53.…”

“…Twist has been shown to be involved in several pathways that control tumor cell growth, apoptosis, differentiation and epithelial-mesenchymal transition (Maestro et al, 1999;Funato et al, 2001;Valsesia-Wittmann et al, 2004;Yang et al, 2004;Alexander et al, 2006). Moreover, Twist inhibits the p53-mediated response to cellular stress (Stasinopoulos et al, 2005). We recently showed that Twist is involved in both drug resistance and tumor growth through YB-1 expression (Shiota et al, 2008).…”

Escape from p53-mediated tumor surveillance in neuroblastoma: switching off the p14ARF-MDM2-p53 axis

“…75 These findings are in agreement with an earlier study that pointed to downregulation of p19 ARF expression by Twist1 as a mechanism for compensating the apoptosis-priming properties of Myc. 76 Several other mechanisms may also contribute to the p53-inhibitory activity of TWIST1, including inhibition of acetyltransferases that serve as transcriptional coactivators for p53, 77 modulation of the activity of a transactivator of the TP53 promoter, 78 prevention of p53 phosphorylation, 78 and direct suppression of the DNA-binding activity of p53. 79 Of note, the TWIST1 and TWIST2 proteins have also recently been shown to prevent oncogene-induced premature senescence with concomitant abrogation of p16 INK4a and p21 WAF1/CIP1 activation, and to induce, in cooperation with activated mitogenic oncoproteins, epithelial-mesenchymal transition, suggesting a role as general inhibitors of multiple oncogene-induced safeguard programs.…”