Deborah Silvera

Translational control in cancer

Remarkable progress has been made in defining a new understanding of the role of mRNA translation and protein synthesis in human cancer. Translational control is a crucial component of cancer development and progression, directing both global control of protein synthesis and selective translation of specific mRNAs that promote tumour cell survival, angiogenesis, transformation, invasion and metastasis. Translational control of cancer is multifaceted, involving alterations in translation factor levels and activities unique to different types of cancers, disease stages and the tumour microenvironment. Several clinical efforts are underway to target specific components of the translation apparatus or unique mRNA translation elements for cancer therapeutics.

Essential role for eIF4GI overexpression in the pathogenesis of inflammatory breast cancer

Inflammatory breast cancer (IBC) is the most lethal form of primary breast cancer. IBC lethality derives from generation of tumour emboli, which are non-adherent cell clusters that rapidly spread by a form of continuous invasion known as passive metastasis. In most cancers, expression of E-cadherin, an epithelial marker, is indicative of low metastatic potential. In IBC, E-cadherin is overexpressed and supports formation of tumour emboli by promoting tumour cell interactions rather than adherence to stroma. E-cadherin, a surface component of adherens junctions, is anchored by interaction with p120 catenin (p120). We show that the unique pathogenic properties of IBC result in part from overexpression of the translation initiation factor eIF4GI in most IBCs. eIF4GI reprograms the protein synthetic machinery for increased translation of mRNAs with internal ribosome entry sites (IRESs) that promote IBC tumour cell survival and formation of tumour emboli. Overexpression of eIF4GI promotes formation of IBC tumour emboli by enhancing translation of IRES-containing p120 mRNAs. These findings provide a new understanding of translational control in the development of advanced breast cancer.

Inflammatory breast cancer cells are constitutively adapted to hypoxia.

We recently showed that overexpression of translation initiation factor eIF4G partially drives the unusual pathological features of Inflammatory Breast Cancer (IBC), the most lethal form of primary breast cancer. IBC has the peculiar feature that, rather than develop as a solid tumor, it typically generates rapidly metastasizing tight clusters of cancer cells referred to as tumor cell emboli, consisting of cancer cells held together by increased membrane expression of E-cadherin. Overexpression of eIF4GI in IBC leads to a specific increase in the translation of internal ribosomal entry site (IRES) containing mRNAs, of which two encode key proteins involved in the pathological features of IBC. One of these mRNAs encodes p120 catenin, which mediates E-cadherin retention at the cell surface, and the other encodes VEGF, which accounts for high levels of IBC angiogenesis and resistance to hypoxia. Here we show that IBC cells have adapted to the persistent hypoxia they experience as tumor emboli by reprogramming the protein synthesis machinery to constitutively translate mRNAs required for IBC cell survival during hypoxia even under normal oxygen (normoxic) conditions. Thus, IBC cells have been able to behave as if they are continuously hypoxic even when they are not.

mTORC1 and 2 coordinate transcriptional and translational reprogramming in resistance to DNA damage and replicative stress in breast cancer cells.

ABSTRACT mTOR coordinates growth signals with metabolic pathways and protein synthesis and is hyperactivated in many human cancers. mTOR exists in two complexes: mTORC1, which stimulates protein, lipid, and ribosome biosynthesis, and mTORC2, which regulates cytoskeleton functions. While mTOR is known to be involved in the DNA damage response, little is actually known regarding the functions of mTORC1 compared to mTORC2 in this regard or the respective impacts on transcriptional versus translational regulation. We show that mTORC1 and mTORC2 are both required to enact DNA damage repair and cell survival, resulting in increased cancer cell survival during DNA damage. Together mTORC1 and -2 enact coordinated transcription and translation of protective cell cycle and DNA replication, recombination, and repair genes. This coordinated transcriptional-translational response to DNA damage was not impaired by rapalog inhibition of mTORC1 or independent inhibition of mTORC1 or mTORC2 but was blocked by inhibition of mTORC1/2. Only mTORC1/2 inhibition reversed cancer cell resistance to DNA damage and replicative stress and increased tumor cell killing and tumor control by DNA damage therapies in animal models. When combined with DNA damage, inhibition of mTORC1/2 blocked transcriptional induction more strongly than translation of DNA replication, survival, and DNA damage response mRNAs.

Hyperactivated mTOR and JAK2/STAT3 pathways: Crucial molecular drivers and potential therapeutic targets of inflammatory breast cancer (IBC).

60 Background: IBC is an aggressive form of breast cancer with poor prognosis. Combined multi-modality Rx results in a 5 year OS of 30-50%, underscoring the unmet need for targeted Rx. Our preclinical research in cell lines and xenografts identifies a role for activated PI3K/mTOR pathway in IBC. IBC cells express IL-6 and IL-8 and recruit tumor activated macrophages (TAMs) that further induce IL-6, IL-8 and activate the JAK2/STAT3 pathway. We investigated the independent and combined activity of these pathways in IBC tissues. METHODS Archived tissues of 42 IBC pts and 13 controls (nl breast) were analyzed using IHC and scored by 3 independent pathologists. Results defined as: 0, 1+ = neg; 2+ = pos for activated mTOR (P-S6) and 0 = neg; 1+, 2+ = pos for activated nuclear JAK2/STAT3 (P-JAK2; P-STAT3), cytokine (IL-6), macrophage (mØ) infiltration (CD68) and TAM (CD163). Proportions of IBC cases with pos expression were compared with controls (Fishers exact tests). Clinical and survival data were obtained. RESULTS Median age at diagnosis: 46 yrs (31-62) in early-stage IBC [EIBC] (n=37) and 41 yrs (29-57) in pts with de novo metastatic IBC [MIBC] (n=5). In EIBC, 19/36: HER2+ (1 unk); 8/19: ER+/HER2+; 8/36: ER-/HER2-. In MIBC, all were ER- (1 unk) and 3/4 were HER2+ (1 unk). 88% Rx with neoadjuvant and/or adjuvant anthracycline and taxane w/o adjuvant trastuzumab. 24 pts died (5/5 MIBC). Median OS: 86 mo (95% CI lower 48 mo) for EIBC & 41 mo (95% CI 8-81 mo) for MIBC. Median RFS: 18 mo (95% CI 18-79 mo) for 23 pts (13 NED; 1 unk). All controls: neg for P-S6, JAK2, STAT3 and TAMs and 92% neg for mØ and IL-6. Proportion of IBC with pos expression when compared to controls listed in table (p <0.0001). Of 31 pts with complete biomarker data who were PS6+, 97% had activated JAK2, 58% had activated STAT3, 80% had strong mØ and TAM infiltration and 97% were IL6+. CONCLUSIONS This is the first study that validates preclinical findings and shows a strong association between mTOR, cytokines, TAMs and JAK/STAT pathways in most IBC pt tissues. Findings suggest a key role for dual blockade of mTOR and JAK/STAT pathways in phase I trials. [Table: see text].