Translational adaptation in breast cancer metastasis and emerging therapeutic opportunities

Breast cancer's tendency to metastasize poses a critical barrier to effective treatment, making it a leading cause of mortality among women worldwide. A growing body of evidence is showing that translational adaptation is emerging as a key mechanism enabling cancer cells to thrive in the dynamic tumor microenvironment (TME). Here, we systematically summarize how breast cancer cells utilize translational adaptation to drive metastasis, highlighting the intricate regulation by specific translation machinery and mRNA attributes such as sequences and structures, along with the involvement of tRNAs and other trans-acting RNAs. We provide an overview of the latest findings and emerging concepts in this area, discussing their potential implications for therapeutic strategies in breast cancer.

Helicases clear hurdles during plant defense protein translation

Plants undergo translational reprogramming when they are under attack by pathogens. Xiang et al. recently revealed that plant helicases induced by pathogen recognition unwind RNA hairpins upstream of the main open reading frames (mORFs), thus allowing ribosomes to bypass the upstream ORFs (uORFs) and translate downstream defense proteins, a mechanism that is also found in mammals.

Global translational induction during NLR-mediated immunity in plants is dynamically regulated by CDC123, an ATP-sensitive protein

The recognition of pathogen effectors by their cognate nucleotide-binding leucine-rich repeat (NLR) receptors activates effector-triggered immunity (ETI) in plants. ETI is associated with correlated transcriptional and translational reprogramming and subsequent death of infected cells. Whether ETI-associated translation is actively regulated or passively driven by transcriptional dynamics remains unknown. In a genetic screen using a translational reporter, we identified CDC123, an ATP-grasp protein, as a key activator of ETI-associated translation and defense. During ETI, an increase in ATP concentration facilitates CDC123-mediated assembly of the eukaryotic translation initiation factor 2 (eIF2) complex. Because ATP is required for the activation of NLRs as well as the CDC123 function, we uncovered a possible mechanism by which the defense translatome is coordinately induced during NLR-mediated immunity. The conservation of the CDC123-mediated eIF2 assembly suggests its possible role in NLR-mediated immunity beyond plants.

Plant translational reprogramming for stress resilience

Organisms regulate gene expression to produce essential proteins for numerous biological processes, from growth and development to stress responses. Transcription and translation are the major processes of gene expression. Plants evolved various transcription factors and transcriptome reprogramming mechanisms to dramatically modulate transcription in response to environmental cues. However, even the genome-wide modulation of a gene's transcripts will not have a meaningful effect if the transcripts are not properly biosynthesized into proteins. Therefore, protein translation must also be carefully controlled. Biotic and abiotic stresses threaten global crop production, and these stresses are seriously deteriorating due to climate change. Several studies have demonstrated improved plant resistance to various stresses through modulation of protein translation regulation, which requires a deep understanding of translational control in response to environmental stresses. Here, we highlight the translation mechanisms modulated by biotic, hypoxia, heat, and drought stresses, which are becoming more serious due to climate change. This review provides a strategy to improve stress tolerance in crops by modulating translational regulation.

PABP/purine-rich motif as an initiation module for cap-independent translation in pattern-triggered immunity

Upon stress, eukaryotes typically reprogram their translatome through GCN2-mediated phosphorylation of the eukaryotic translation initiation factor, eIF2α, to inhibit general translation initiation while selectively translating essential stress regulators. Unexpectedly, in plants, pattern-triggered immunity (PTI) and response to other environmental stresses occur independently of the GCN2/eIF2α pathway. Here, we show that while PTI induces mRNA decapping to inhibit general translation, defense mRNAs with a purine-rich element ("R-motif") are selectively translated using R-motif as an internal ribosome entry site (IRES). R-motif-dependent translation is executed by poly(A)-binding proteins (PABPs) through preferential association with the PTI-activating eIFiso4G over the repressive eIF4G. Phosphorylation by PTI regulators mitogen-activated protein kinase 3 and 6 (MPK3/6) inhibits eIF4G's activity while enhancing PABP binding to the R-motif and promoting eIFiso4G-mediated defense mRNA translation, establishing a link between PTI signaling and protein synthesis. Given its prevalence in both plants and animals, the PABP/R-motif translation initiation module may have a broader role in reprogramming the stress translatome.

KLF16 enhances stress tolerance of colorectal carcinomas by modulating nucleolar homeostasis and translational reprogramming

Translational reprogramming is part of the unfolded protein response (UPR) during endoplasmic reticulum (ER) stress, which acts to the advantage of cancer growth and development in different stress conditions. But the mechanism of ER stress-related translational reprogramming in colorectal carcinoma (CRC) progression remains unclear. Here, we identified that Krüppel-Like Factor 16 (KLF16) can promote CRC progression and stress tolerance through translational reprogramming. The expression of KLF16 was upregulated in CRC tissues and associated with poor prognosis for CRC patients. We found that ER stress inducers can recruit KLF16 to the nucleolus and increase its interaction with two essential proteins for nucleolar homeostasis, nucleophosmin1 (NPM1) and fibrillarin (FBL). Moreover, knockdown of KLF16 can dysregulate nucleolar homeostasis in CRC cells. Translation-reporter system and polysome profiling assays further showed that KLF16 can effectively promote cap-independent translation of ATF4, which can enhance ER-phagy and proliferation of CRC cells. Overall, our study unveils a previously unrecognized role for KLF16 as an ER stress regulator through mediating translational reprogramming to enhance stress tolerance of CRC cells and provides a potential therapeutic vulnerability.

Long non-coding RNA TINCR suppresses metastatic melanoma dissemination by preventing ATF4 translation

Transition from proliferative‐to‐invasive phenotypes promotes metastasis and therapy resistance in melanoma. Reversion of the invasive phenotype, however, is challenged by the poor understanding of mechanisms underlying its maintenance. Here, we report that the lncRNA TINCR is down‐regulated in metastatic melanoma and its silencing increases the expression levels of invasive markers, in vitro migration, in vivo tumor growth, and resistance to BRAF and MEK inhibitors. The critical mediator is ATF4, a central player of the integrated stress response (ISR), which is activated in TINCR‐depleted cells in the absence of starvation and eIF2α phosphorylation. TINCR depletion increases global protein synthesis and induces translational reprogramming, leading to increased translation of mRNAs encoding ATF4 and other ISR proteins. Strikingly, re‐expression of TINCR in metastatic melanoma suppresses the invasive phenotype, reduces numbers of tumor‐initiating cells and metastasis formation, and increases drug sensitivity. Mechanistically, TINCR interacts with mRNAs associated with the invasive phenotype, including ATF4, preventing their binding to ribosomes. Thus, TINCR is a suppressor of the melanoma invasive phenotype, which functions in nutrient‐rich conditions by repressing translation of selected ISR RNAs.

LncRNAs in Cancer: From garbage to Junk

Sequencing-based transcriptomics has significantly redefined the concept of genome complexity, leading to the identification of thousands of lncRNA genes identification of thousands of lncRNA genes whose products possess transcriptional and/or post-transcriptional regulatory functions that help to shape cell functionality and fate. Indeed, it is well-established now that lncRNAs play a key role in the regulation of gene expression through epigenetic and posttranscriptional mechanims. The rapid increase of studies reporting lncRNAs alteration in cancers has also highlighted their relevance for tumorigenesis. Herein we describe the most prominent examples of well-established lncRNAs having oncogenic and/or tumor suppressive activity. We also discuss how technical advances have provided new therapeutic strategies based on their targeting, and also report the challenges towards their use in the clinical settings.

Regulation of Translation in the Protozoan Parasite Leishmania

Leishmaniasis represents a serious health problem worldwide and drug resistance is a growing concern. Leishmania parasites use unusual mechanisms to control their gene expression. In contrast to many other species, they do not have transcriptional regulation. The lack of transcriptional control is mainly compensated by post-transcriptional mechanisms, including tight translational control and regulation of mRNA stability/translatability by RNA-binding proteins. Modulation of translation plays a major role in parasite survival and adaptation to dramatically different environments during change of host; however, our knowledge of fine molecular mechanisms of translation in Leishmania remains limited. Here, we review the current progress in our understanding of how changes in the translational machinery promote parasite differentiation during transmission from a sand fly to a mammalian host, and discuss how translational reprogramming can contribute to the development of drug resistance.

tiRNAs: A novel class of small noncoding RNAs that helps cells respond to stressors and plays roles in cancer progression

tRNA-derived stress-induced RNAs (tiRNAs), important components of tRNA-derived fragments, are gaining popularity for their functions as small noncoding RNAs involved in cancer progression. Under cellular stress, tiRNAs are generated when mature tRNA is specifically cleaved by angiogenin and suggested to act as transducers or effectors involved in cellular stress responses. tiRNAs facilitate cells to respond to stresses mainly via reprogramming translation, inhibiting apoptosis, degrading mRNA, and generating stress granules. This review introduces the cellular biogenesis, molecular mechanisms, and biological roles of tiRNAs in stress response and disease regulation. A better understanding of their roles in regulating cancer may provide novel biomarkers or therapeutic targets for diagnosis and treatment.

Translational Control under Stress: Reshaping the Translatome

Adequate reprogramming of cellular metabolism in response to stresses or suboptimal growth conditions involves a myriad of coordinated changes that serve to promote cell survival. As protein synthesis is an energetically expensive process, its regulation under stress is of critical importance. Reprogramming of messenger RNA (mRNA) translation involves well-understood stress-activated kinases that target components of translation initiation machinery, resulting in the robust inhibition of general translation and promotion of the translation of stress-responsive proteins. Translational arrest of mRNAs also results in the accumulation of transcripts in cytoplasmic foci called stress granules. Recent studies focus on the key roles of transfer RNA (tRNA) in stress-induced translational reprogramming. These include stress-specific regulation of tRNA pools, codon-biased translation influenced by tRNA modifications, tRNA miscoding, and tRNA cleavage. In combination, signal transduction pathways and tRNA metabolism changes regulate translation during stress, resulting in adaptation and cell survival. This review examines molecular mechanisms that regulate protein synthesis in response to stress.

Post-transcriptional control of gene expression following stress: the role of RNA-binding proteins

The ability of mammalian cells to modulate global protein synthesis in response to cellular stress is essential for cell survival. While control of protein synthesis is mediated by the regulation of eukaryotic initiation and elongation factors, RNA-binding proteins (RBPs) provide a crucial additional layer to post-transcriptional regulation. RBPs bind specific RNA through conserved RNA-binding domains and ensure that the information contained within the genome and transcribed in the form of RNA is exported to the cytoplasm, chemically modified, and translated prior to folding into a functional protein. Thus, this group of proteins, through mediating translational reprogramming, spatial reorganisation, and chemical modification of RNA molecules, have a major influence on the robust cellular response to external stress and toxic injury.

JIP60-mediated, jasmonate- and senescence-induced molecular switch in translation toward stress and defense protein synthesis

Two closely related genes encoding the jasmonate-induced protein 60 (JIP60) were identified in the barley genome. The gene on chromosome arm 4HL encodes the previously identified protein encoded by the cDNA X66376.1. This JIP60 protein is characterized here and shown to consist of two domains: an NH2-terminal domain related to ribosome-inactivating proteins and a COOH-terminal domain, which displays similarity to eukaryotic translation initiation factor 4E (eIF4E). JIP60 undergoes processing in vivo, as a result of which JIP60's COOH-terminal eIF4E domain is released and functions in recruiting a subset of cellular messengers for translation. This effect was observed for both MeJA-treated and naturally senescing plants. Because the JIP60 gene is in close proximity to several quantitative trait loci for both biotic and abiotic stress resistance, our results identify a unique target for future breeding programs.