Protumorigenic role of Timeless in hepatocellular carcinoma

Abstract

Abstract. The mammalian timeless (TIM) protein interacts with proteins of the endogenous clock and essentially contributes to the circadian rhythm. In addition, TIM is involved in maintenance of chromosome integrity, growth control and development. Thus, we hypothesized that TIM may exert a potential protumorigenic function in human hepatocarcinogenesis. TIM was overexpressed in a subset of human HCCs both at the mRNA and the protein level. siRNA-mediated knockdown of TIM reduced cell viability due to the induction of apoptosis and G2 arrest. The latter was mediated via CHEK2 phosphorylation. In addition, siRNA-treated cells showed a significantly reduced migratory capacity and reduced expression levels of various proteins. Mechanistically, TIM directly interacts with the eukaryotic elongation factor 1A2 (EEF1A2), which binds to actin filaments to promote tumor cell migration. siRNA-mediated knockdown of TIM reduced EEF1A2 protein levels thereby affecting ribosomal protein biosynthesis. Thus, overexpression of TIM exerts oncogenic function in human HCCs, which is mediated via CHEK2 and EEF1A2. IntroductionMany biological processes show a circadian rhythm, which is controlled by an endogenous clock that synchronizes with day and night phases of the solar day. The periodical rhythm is generated by a molecular oscillator located in the suprachiasmatic nuclei of the hypothalamus, which controls peripheral oscillators in virtually any other cell (1). The circadian clock is organized through a complex network of transcriptiontranslational feedback loops that drive rhythmic expression patterns of core clock components in mammals (2).The Timeless (TIM) protein interacts with clock proteins and is essential for generation of a circadian rhythm in flies (3). In addition, phylogenetic sequence analysis revealed the presence of a paralogue in D. melanogaster (4), which is not involved in the core clock machinery, but is important for the maintenance of chromosome integrity, growth control, and development. In contrast, a single TIM gene has been identified in mammals, which acquired all of these functions as indicated by its role in DNA damage response, replication, and circadian rhythm (5-9). Consistently, TIM knockout resulted in embryonic lethality in mice (10). In addition, TIM and other clock genes have been linked to human carcinogenesis (11)(12)(13)(14). Using integrative molecular profiling we have recently identified that inactivation of Period homolog 3, a component of the clock machinery, occurs in human HCC indicating that dysregulation of this regulatory network may contribute to hepatocarcinogenesis (15).The eukaryotic elongation factor 1-α (EEF1A), a member of the G protein family, represents one of the four subunits that constitute the eukaryotic elongation factor 1 (16). In humans,

<p>MicroRNA-708 Suppresses Cell Proliferation and Enhances Chemosensitivity of Cervical Cancer Cells to cDDP by Negatively Targeting Timeless</p>

“…3 Additionally, an increasing number of studies have found that Timeless is over-expressed in several tumor types, including lung cancer, breast cancer, hepatocellular cancer, and cervical cancer. 4,[5][6][7][8] Furthermore, aberrant Timeless expression is associated with poor survival in lung cancer, breast cancer, and cervical carcinoma, 4,6,8 indicating that Timeless plays a substantial role in these malignancies. Besides, recent studies have shown that Timeless is involved in the regulation of homologous recombination (HR) and nonehomologous end joining (NHEJ) repair, which are two important methods to repair DNA damage by interacting with poly (ADP-ribose) polymerase-1 (PARP-1).…”

TIMELESS contributes to the progression of breast cancer through activation of MYC

“…Recently, TIM has been reported to be upregulated in various human tumor types and to be involved in cancer development and progression [10, 11]. In bladder cancer, TIM expression is correlated with risk of progression to muscle-invasive disease [12].…”

“…TIM is upregulated in lung cancer, and patients with high TIM expression have a poor prognosis [10]. Knockdown of TIM in hepatocellular carcinoma cells induces apoptosis, arrests cell cycle in the G2 phase, and inhibits cell migration by perturbing the interaction with eukaryotic elongation factor 1A2 (EEF1A2) [11]. Moreover, TIM is upregulated in tissue in metastatic prostate cancer, and TIM knockdown in prostate cancer cell PC3M suppresses cell migration [13].…”

Evaluating the associations between human circadian rhythms and dysregulated genes in liver cancer cells

“…Rhythmic fluctuations have been identified in hepatic metabolic functions with a 24-h periodicity ( 22 ). Previous studies have demonstrated that liver cancer initiation may be due to alterations in circadian rhythmic genes, including PER3 ( 23 ) and CRY genes, and casein kinases ( 24 ). Additionally, it has been revealed that the dysregulation of metallothionein-1 (MT-1), MT-2 and metal transcription factor-1 are involved in the alterations to circadian rhythms present in liver cancer ( 25 ).…”