Lin28 Overexpression Research Articles

LIN28 upregulation in primary human T cells impaired CAR T antitumoral activity.

LIN28, a highly conserved RNA-binding protein that acts as a posttranscriptional modulator, plays a vital role in the regulation of T-cell development, reprogramming, and immune activity in infectious diseases and T-cell-based immunotherapies. LIN28 inhibit the expression of let-7 miRNAs, the most prevalent family of miRNAs in lymphocytes. Recently it has been suggested that let-7 enhances murine anti-tumor immune responses. Here, we investigated the impact of LIN28 upregulation on human T cell functions, focusing on its influence on CAR T cell therapy. LIN28 lentiviral transduction of human T cells led to a stable expression of LIN28 that significantly downregulated the let-7 miRNA family without affecting cell viability or expansion potential. LIN28 overexpression maintained human T cell phenotype markers and functionality but impaired the antitumoral cytotoxicity of NKG2D-CAR T cells both in vitro and in vivo. These findings highlight the intricate relationship between LIN28/let-7 axis and human T cell functionality, including in CAR T cell therapy.

Lin28 promoting the protective effect of PMSCs on hepatic ischaemia-reperfusion injury by regulating glucose metabolism.

Human placental mesenchymal stem cells (PMSCs) can prevent liver ischaemia-reperfusion injury (LIRI). However, their therapeutic effects are limited. Therefore, additional research is required to elucidate the mechanisms of PMSC-mediated LIRI prevention and enhance the related therapeutic effects. This study aimed to examine the role of the Lin28 protein in the regulation of glucose metabolism in PMSCs. Further, it explored whether Lin28 could enhance the protective effects of PMSCs against LIRI and investigated the underlying mechanisms. Western blotting was performed to examine Lin28 expression in PMSCs under hypoxic conditions. A Lin28 overexpression construct was introduced into PMSCs, and the effect on glucose metabolism was examined using a glucose metabolism kit. Further, the expression of some proteins involved in glucose metabolism and the PI3K-AKT pathway and the levels of microRNA Let-7a-g were examined using western blots and real-time quantitative PCR, respectively. To examine the relationship between Lin28 and the PI3K-Akt pathway, the effects of AKT inhibitor treatment on the changes induced by Lin28 overexpression were examined. Subsequently, AML12 cells were co-cultured with PMSCs to elucidate the mechanisms via which PMSCs prevent hypoxic injury in liver cells in vitro. Finally, C57BL/6J mice were used to establish a partial warm ischaemia-reperfusion model. The mice received intravenous injections containing PMSCs (control and Lin28-overexpressing PMSCs). Finally, their serum transaminase levels and degree of liver injury were assessed using biochemical and histopathological methods, respectively. Lin28 was upregulated under hypoxic conditions in PMSCs. Lin28 exerted protective effects against hypoxia-induced cell proliferation. Moreover, it increased the glycolytic capacity of PMSCs, allowing PMSCs to produce more energy under hypoxic conditions. Lin28 also activated the PI3K-Akt signalling pathway under hypoxic conditions, and its effects were attenuated by AKT inhibition. Lin28 overexpression could protect cells against LIRI-induced liver damage, inflammation and apoptosis and could also attenuate hypoxia-induced hepatocyte injury. Lin28 enhances glucose metabolism under hypoxic conditions in PMSCs, thereby exerting protective effects against LIRI by activating the PI3K-Akt signalling pathway. Our study is the first to report the potential of genetically modified PMSCs for LIRI treatment.

RNA-binding protein complex LIN28/MSI2 enhances cancer stem cell-like properties by modulating Hippo-YAP1 signaling and independently of Let-7

The RNA binding protein LIN28 directly modulates the stability and translation of target mRNAs independently of Let-7; however, the key downstream targets of LIN28 in this process are largely unknown. Here, we revealed that Hippo signaling effector YAP1 functioned as a key downstream regulator of LIN28 to modulate the cancer stem cell (CSC)-like properties and tumor progressions in triple negative breast cancer (TNBC). LIN28 was overexpressed in BC tissues and cell lines, and significantly correlated with poorer overall survivals in patients. Ectopic LIN28 expression enhanced, while knockdown of LIN28A inhibited the CSC-like properties, cell growth and invasive phenotypes of TNBC cells in vitro and in vivo. Transcriptome analysis demonstrated LIN28 overexpression significantly induced the expressions of YAP1 downstream genes, while reduced the transcripts of YAP1 upstream kinases, such as MST1/2 and LATS1/2, and knockdown of LIN28A exhibited the opposite effects. Furthermore, constitutive activation of YAP1 in LIN28 knockdown TNBC cells could rescue the cell growth and invasive phenotypes in vitro and in vivo. Mechanistically, instead of the dependence of Let-7, LIN28 recruited RNA binding protein MSI2 in a manner dependent on the LIN28 CSD domain and MSI2 RRM domain, to directly induce the mRNA decay of YAP1 upstream kinases, leading to the inhibition of Hippo pathway and activation of YAP1, which eventually gave rise to increased CSC populations, enhanced tumor cell growth and invasive phenotypes. Accordingly, co-upregulations of LIN28 and MSI2 in TNBC tissues were strongly associated with YAP1 protein level and tumor malignance. Taken together, our findings unravel a novel LIN28/MSI2-YAP1 regulatory axis to induce the CSC-like properties, tumor growth and metastasis, independently of Let-7, which may serve as a potential therapeutic strategy for the treatment of a subset of TNBC with LIN28 overexpression.

ETMR-18. TARGETING Lin28 IN ETMR WITH ODC1 INHIBITOR DFMO

Embryonal tumor with multilayered rosettes (ETMR), is an aggressive brain tumor primarily occurring in young patients (<4 years of age) and characterized by C19MC amplification and Lin28 overexpression. These genetic hallmarks have been shown to participate in driving ETMR in a C19MC-Lin28-MYCN circuit. Reducing Lin28 disrupts this circuit and reduces cell viability in ETMR models. Investigation of therapeutic agents targeting this pathway is required to provide new treatment options for this deadly disease. We present data showing the effect of DFMO (α-difluoromethylornithine) in ETMR, an ODC1 inhibitor known to reduce Lin28 in neuroblastoma. DFMO treatment of the ETMR cell line BT-183 resulted in a significant reduction of intracellular Lin28 protein levels (P<0.05) as indicated by flow cytometry. In concert with this reduction in Lin28, there was a as significant reduction in viable cells (P<0.05), and the number of CD133+ cells were reduced 2-fold (P<0.05). High throughput drug testing of BT-183 identified a number of additional therapeutic agents with potential therapeutic efficacy for ETMR and combining these with cytostatic agent DFMO demonstrated the potential use of these drugs in combination. These in vitro data were complemented by testing of DFMO in an in vivo stereotaxic xenograft ETMR model, with inhibition of tumor burden monitored by bioluminescent imaging of the tumors. Together this work shows that Lin28 targeting agents such as DFMO merit further examination and integrating these types of agents into treatment strategies for ETMR may lead to better outcomes.

Lin28 reprograms inner ear glia to a neuronal fate.

Sensorineural hearing loss is irreversible and can be caused by loss of auditory neurons. Regeneration of neural cells from endogenous cells may offer a future tool to restore the auditory circuit and to enhance the performance of implantable hearing devices. Neurons and glial cells in the peripheral nervous system are closely related and originate from a common progenitor. Prior work in our lab indicated that in the early postnatal mouse inner ear, proteolipid protein 1 (Plp1) expressing glial cells could act as progenitor cells for neurons in vitro. Here, we used a transgenic mouse model to transiently overexpress Lin28, a neural stem cell regulator, in Plp1-positive glial cells. Lin28 promoted proliferation and conversion of auditory glial cells into neurons in vitro. To study the effects of Lin28 on endogenous glial cells after loss of auditory neurons in vivo, we produced a model of auditory neuropathy by selectively damaging auditory neurons with ouabain. After neural damage was confirmed by the auditory brainstem response, we briefly upregulated the Lin28 in Plp1-expressing inner ear glial cells. One month later, we analyzed the cochlea for neural marker expression by quantitative RT-PCR and immunohistochemistry. We found that transient Lin28 overexpression in Plp1-expressing glial cells induced expression of neural stem cell markers and subsequent conversion into neurons. This suggests the potential for inner ear glia to be converted into neurons as a regeneration therapy for neural replacement in auditory neuropathy.

Overexpression of Lin28a delays Xenopus metamorphosis and down-regulates albumin independently of its translational regulation domain.

Lin28 regulates stem cell biology and developmental timing. At the molecular level Lin28 inhibits the biogenesis of the micro RNA let-7 and directly controls the transcription and translation of several genes. In Xenopus, Lin28 overexpression delays metamorphosis and affects the expression of genes of the thyroid hormone (TH) axis. The TH carrier albumin, synthesized by the liver, is down-regulated in limbs and tail after Lin28 overexpression. The molecular mechanisms underlying the interaction between Lin28, let-7, and the hypothalamus-pituitary-thyroid gland (HPT) axis are unknown. We found that precursor and mature forms of let-7 increase during Xenopus metamorphosis. In the liver, lin28b is down-regulated and albumin is up-regulated during metamorphosis. Overexpression of a truncated form of Lin28a (Lin28aΔC), which has been shown not to interact with RNA helicase A to regulate translation, delays metamorphosis, indicating that the translational regulation domain is not required to inhibit the HPT axis. Importantly, both full length Lin28a and Lin28aΔC block the increase of albumin mRNA in the liver independently of changes in TH signaling. These results suggest that Lin28 delays metamorphosis through regulation of let-7 and that the decrease of the TH carrier albumin is one of the early changes after Lin28 overexpression.

Lin28a expression protects against streptozotocin-induced β-cell destruction and prevents diabetes in mice.

Lin28, which is highly expressed during embryogenesis, has been shown to play an important role in cell growth and embryonic development. Meanwhile, Lin28 represses let-7 miRNA biogenesis and block pre-let-7 processing in the cytoplasm. The let-7 family of miRNAs is known to repress oncogenesis and cell cycle progression by targeting oncogenic genes and signalling pathways. Consequently, Lin28 acts as an oncogene by upregulating let-7 targets through the repression of let-7 biogenesis. A recent genome-wide association study (GWAS) showed that many genes related to Type 2 diabetes (T2D) are also oncogenes or cell cycle regulators. The role of Lin28 in mouse growth and glucose metabolism in metabolic-related tissues has also been studied. In these studies, whole-body Lin28 overexpression was found to promote glucose utilization and prevent weight gain by inhibiting let-7 biogenesis. Furthermore, Lin28 has been found to directly stimulate skeletal myogenesis and cell growth. Therefore, we determined whether similar effects mediated by Lin28a, which is essential for cell growth and proliferation, may also apply to pancreatic ß-cells. We found that overexpression of Lin28a protects pancreatic β-cells from streptozotocin (STZ)-induced β-cell destruction in vitro and in vivo. Furthermore, Lin28a-overexpressing transgenic (Tg) mice had higher insulin secretion in the presence of glucose than in control mice. Our findings suggest that the Lin28/let-7 axis is an important regulator of pancreatic β-cell functions and that precise modulation of this axis may be helpful in treating metabolic diseases such as diabetes. SIGNIFICANCE OF THE STUDY: We demonstrate that Lin28a prevents pancreatic β-cell death against streptozotocin (STZ)-induced β-cell destruction in vitro and in vivo. Furthermore, Lin28a promotes cell survival and proliferation by activating the PI3K-Akt signalling pathway, which may be dependent on let-7 regulation. Taken together, our results imply that the Lin28a/let-7 axis is an important regulator of pancreatic β-cell functions and that precise modulation of this axis may be helpful in treating metabolic diseases such as diabetes.

Abstract 540: β-Catenin/LIN28B promotes cell proliferation of human trophoblast cells via let7a repression

Abstract LIN28 is a highly conserved RNA-binding proteins, have been implicated in key biological functions such as development, glucose metabolism and pluripotency. LIN28 overexpression induces the reprogramming of pluripotent stem cells (iPSCs) and supports the proliferative and metabolic capacities of iPSCs. Therefore LIN28 is crucial for the regulation of the cell fate and human embryonic development. In addition, LIN28B is frequently up-regulated in a variety of cancers and correlates with poor prognosis and cancer recurrence, indicating the crucial role of LIN28B in tumorigenesis. Aberrantly expression of LIN28B is responsible for the decrease in the let-7 microRNA family observed in many cancers and Let-7 is frequently down-regulated in numerous different tumors and lower levels of let-7 correlates with poor prognosis. Therefore, LIN28/Let7 may be crucial for the regulation of cell cycle and cell proliferation. In our present study, We first detected the expression of LIN28B in normal placental villi and choriocarcinoma tissue. Our data showed LIN28B was highly expressed in human choriocarcinoma tissues and most LIN28B staining was localized in the nucleus. Comparatively, LIN28B staining was faint in normal placental villi. Our data then demonstrated that LIN28B was highly expressed in human choriocarcinoma cell lines JEG-3 and JAR. However, LIN28B expression was undetectable in HTR-8/Svneo normal trophoblast cells. Our data then demonstrated that LIN28B knockdown by small interfering RNA (siRNA) caused an increase in Let-7a expression. Further, silencing of LIN28 inhibited IGF2BP1 expression and suppressed cell proliferation capacity, which can be markedly restored by Le7a siRNA. These findings reveal that LIN28 may promote IGF2BP1 expression and cell proliferation by Let-7a repression. Moreover, β-catenin knockdown resulted in reduced LIN28 expression and Let-7a up-regulation. β-catenin is the major mediator of canonical Wnt signaling pathway, and activation of canonical Wnt signaling has been reported to play a critical role in the proliferation, invasion, and differentiation of various tumors. Collectively, our present data indicated that β-catenin/LIN28B/Let7a pathway may be crucial for cell proliferation regulation in human choriocarcinoma cells. Citation Format: Jing Wu, Baoxin Luan, Huandi Yu, Yinhua Yu, Congjian Xu, Hongbo Zhao. β-Catenin/LIN28B promotes cell proliferation of human trophoblast cells via let7a repression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 540.

Lin28 overexpression inhibits neurite outgrowth of primary cortical neurons in vitro

Lin28 has been shown to promote proliferation of progenitors and survival of neurons during cortical neurogenesis. However, the role of Lin28 in the terminal maturation of neurons remains obscured. In this study, we investigated the developmental impact of Lin28 overexpression on neurite outgrowth. Lin28 expression was upregulated by in utero electroporation at E14.5. Two days later, electroporated cortices were dissociated for culturing primary cortical neurons. We found that Lin28 overexpression, which was confirmed immunocytochemically, led to neurite underdevelopment for all time points during culture. Specifically, Lin28-overexpressing cells displayed significantly fewer primary neurites and a decreased dendritic branching index, compared to GFP-expressing controls. Additionally, Lin28 overexpression in primary cortical neurons induced the expression of high mobility group AT-Hook 2 (HMGA2). Taken together, our study demonstrates that constitutive Lin28 expression disrupts cortical neurogenesis resulting in impaired neurite outgrowth with a concomitant induction of HMGA2.

The heterochronic gene Lin28 regulates amphibian metamorphosis through disturbance of thyroid hormone function

Metamorphosis is a classic example of developmental transition, which involves important morphological and physiological changes that prepare the organism for the adult life. It has been very well established that amphibian metamorphosis is mainly controlled by Thyroid Hormone (TH). Here, we show that the heterochronic gene Lin28 is downregulated during Xenopus laevis metamorphosis. Lin28 overexpression before activation of TH signaling delays metamorphosis and inhibits the expression of TH target genes. The delay in metamorphosis is rescued by incubation with exogenous TH, indicating that Lin28 works upstream or parallel to TH. High-throughput analyses performed before any delay on metamorphosis or change in TH signaling showed that overexpression of Lin28 reduces transcript levels of several hormones secreted by the pituitary, including the Thyroid-Stimulating Hormone (TSH), and regulates the expression of proteins involved in TH transport, metabolism and signaling, showing that Lin28 disrupts TH function at different levels. Our data demonstrates that the role of Lin28 in controlling developmental transitions is evolutionary conserved and establishes a functional interaction between Lin28 and thyroid hormone function introducing a new regulatory step in perinatal development with implications for our understanding of endocrine disorders.

Sevoflurane inhibits embryonic stem cell self-renewal and subsequent neural differentiation by modulating the let-7a-Lin28 signaling pathway.

The commonly used inhalational anesthetic, sevoflurane, can cause toxicity to the central nervous system of the developing fetus. Lin28 has been reported to regulate let-7a, thereby modulating embryo development, neurodegeneration, and even neuron-related tumorigenesis. We demonstrate that pregnant mice receiving sevoflurane treatment during the early stage of pregnancy give birth to fewer offspring presenting a lower birth weight. We have also treated mouse embryonic stem cells (mESCs) with sevoflurane for 6h and determined that mESCs self-renewal is repressed, and that differentiation is initiated earlier than in controls. We have induced neural differentiation in the treated mESCs and determined that their neurogenesis is weakened. Furthermore, sevoflurane upregulates the level of let-7a, which might repress mESC self-renewal by directly targeting the Lin28 3'-untranslated region. Lin28 overexpression attenuates the influence of sevoflurane or of let-7a on the self-renewal of mESCs and their subsequent neural differentiation. The let-7a inhibitor also abolishes the influence of sevoflurane. Thus, the let-7a-Lin28 pathway is involved in the sevoflurane-induced inhibition of ESC self-renewal and subsequent neurogenesis. Our study demonstrates the molecular mechanism underlying the side effects of sevoflurane during early development, laying the foundation for studies on the safe and reasonable usage of other inhalational anesthetics.

Mechanism of Dis3l2 substrate recognition in the Lin28-let-7 pathway.

Summary paragraphThe pluripotency factor Lin28 inhibits the biogenesis of the let-7 family of mammalian microRNAs1–4. Lin28 is highly expressed in embryonic stem cells and has a fundamental role in regulation of development5, glucose metabolism6 and tissue regeneration7. Alternatively, Lin28 overexpression is correlated with the onset of numerous cancers8, while let-7, a tumor suppressor, silences several human oncogenes5. Lin28 binds to precursor let-7 (pre-let-7) hairpins9, triggering the 3' oligo-uridylation activity of TUT4/710–12. The oligoU tail added to pre-let-7 serves as a decay signal, as it is rapidly degraded by Dis3L213,14, a homolog of the catalytic subunit of the RNA exosome. The molecular basis of Lin28 mediated recruitment of TUT4/7 to pre-let-7 and its subsequent degradation by Dis3L2 is largely unknown. To examine the mechanism of Dis3L2 substrate recognition we determined the structure of mouse Dis3L2 in complex with an oligoU RNA to mimic the uridylated tail of pre-let-7. Three RNA binding domains form an open funnel on one face of the catalytic domain that allows RNA to navigate a path to the active site different from its exosome counterpart. The resulting path reveals an extensive network of uracil-specific interactions spanning the first twelve nucleotides of an oligoU-tailed RNA. We identify three U-specificity zones that explain how Dis3L2 recognizes, binds and processes uridylated pre-let-7 in the final step of the Lin28/let-7 pathway.

Lin28 Induces Epithelial-to-Mesenchymal Transition and Stemness via Downregulation of Let-7a in Breast Cancer Cells

The RNA-binding protein Lin28 is known to promote malignancy by inhibiting the biogenesis of let-7, which functions as a tumor suppressor. However, the role of the Lin28/let-7 axis in the epithelial-to-mesenchymal transition (EMT) and stemness in breast cancer has not been clearly expatiated. In our previous study, we demonstrated that let-7 regulates self-renewal and tumorigenicity of breast cancer stem cells. In the present study, we demonstrated that Lin28 was highly expressed in mesenchymal (M) type cells (MDA-MB-231 and SK-3rd), but it was barely detectable in epithelial (E) type cells (MCF-7 and BT-474). Lin28 remarkably induced the EMT, increased a higher mammosphere formation rate and ALDH activity and subsequently promoted colony formation, as well as adhesion and migration in breast cancer cells. Furthermore, we demonstrated that Lin28 induced EMT in breast cancer cells via downregulation of let-7a. Strikingly, Lin28 overexpression was found in breast cancers that had undergone metastasis and was strongly predictive of poor prognoses in breast cancers. Given that Lin28 induced the EMT via let-7a and promoted breast cancer metastasis, Lin28 may be a therapeutic target for the eradication of breast cancer metastasis.

Lin28 regulates HER2 and promotes malignancy through multiple mechanisms

The RNA binding protein Lin28 and its paralog Lin28B are associated with advanced human malignancies. Blocking the biogenesis of let-7 miRNA, a tumor suppressor, by Lin28/Lin28B has been thought to underlie their roles in cancer. Here we report that the mRNA for the human epidermal growth factor receptor 2 (HER2), a HER-family receptor tyrosine kinase known to play a critical role in cell proliferation and survival and also a major therapeutic target in breast cancer, is among several targets of Lin28 regulation. We show that Lin28 stimulates HER2 expression at the posttranscriptional level, and that enforced Lin28 expression promotes cancer cell growth via multiple mechanisms. Consistent with its pleiotropic role in regulating gene expression, Lin28 overexpression in primary breast tumors is a powerful predictor of poor prognosis, representing the first report on the impact of Lin28 expression on clinical outcome in human cancer. While revealing another layer of regulation of HER2 expression in addition to gene amplification, our studies also suggest novel mechanistic insights linking Lin28 expression to disease outcome and imply that targeting multiple pathways is a common mechanistic theme of Lin28-mediated regulation in cancer.

Abstract 1017: Protooncogenic TLR4 generates NANOG-dependent tumor-initiating stem-like cells through LIN28-Let7 pathway in experimental and clinical carcinogenesis

Abstract [Background] TLR4 signaling activated by alcohol/obesity-associated endotoxemia, induces the stem cell marker Nanog to generate tumor-initiating stem-like cells (TISCs) and liver tumors in the HCV nonstructural protein Ns5a transgenic (Tg) mice but not in wild type or Ns5a Tg mice deficient in TLR4 (Machida and Tsukamoto, PNAS, 2009). However, it is unknown whether the TLR4-NANOG pathway serves as a universal oncogenic signaling in the genesis of TISCs and HCC in other etiological animal models and patients or how TLR4 is upregulated in TLR4-NANOG-dependent TISCs. [Aim] We aimed to determine whether TLR4 is a putative proto-oncogene for TIC in liver oncogenesis due to different etiologies and how TLR4 is regulated at the transcriptional and epigenetic levels. [Methods] CD133+/CD49f+ TISCs were isolated using FACS from HCC developed in HCV Core Tg mice fed alcohol, diethylnitrosamine (DEN)-treated mice, and alcoholic patients with or without HCV infection. We generated Tg mice with liver-selective overexpression of constitutively active (ca) TLR4 using LAP promoter-driven tTA and Tet-caTLR4. TLR4 promoter-reporter analysis was performed on TISCs from alcohol-fed Core Tg mice. [Results] CD133+/CD49f+ cells isolated from the animal models and patients are tumorigenic both in vitro and in a xenograft model, and TLR4 or NANOG silencing with shRNA attenuates their tumor initiating property. Hepatocyte specific expression of caTLR4 results in spontaneous development of HCC in 35% of the mice. LIN28 and TLR4 expression is 6-fold higher in TISCs compared to CD133-/CD49f+ cells, and the expression of LIN28 increases TLR4 expression with reduction of Let7 microRNA in CD133- cells but not TISCs, suggesting LIN28-mediated Let7 reduction drive TLR4 induction. TLR4 expression and promoter activity are further reduced by a silencing of LIN28 or expression of Let7. LIN28 and NANOG overexpression transform liver stem cells through activation of TLR4-NANOG pathway. [Conclusions] These results demonstrate that CD133+/CD49f+ cells are TLR4/NANOG-dependent TISCs in both experimental and clinical HCC. TLR4 is induced by LIN28 signaling and is a universal proto-oncogene responsible for the genesis of TLR4-NANOG dependent TISCs, and this pathway serves as a novel therapeutic target for HCC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1017. doi:1538-7445.AM2012-1017

Abstract 4192: LIN28 mRNA targets in breast cancer cells

Abstract LIN28 is a RNA binding protein and a pluripotency factor. It represses tumor suppressing microRNA let-7 and activates let-7 oncogene targets such as HMGA2 and c-Myc. Recent reports show that LIN28 overexpression promotes tumor cell migration and cellular transformation through repression of let-7, and that overexpression is associated with advanced stages of disease, including breast cancer. The molecular function and mode of action of LIN28 in breast cancer is not yet elucidated. To further understand the function of LIN28, we explored LIN28 mRNA targets in breast cancer cells using RNA-protein immunoprecipitation (RIP) followed by RNA sequencing (RIP-Seq). Only 418 genes (1.7% of the human total genes) are enriched more than 1.0 RPKM (reads per kilobase of exon model per million mapped reads) in the LIN28 RIP relative to control RIP. LIN28 mRNA targets in breast cancer cells function in processes that drive tumorigenesis, including cell proliferation, inflammation and metastasis. Therapeutic drugs inhibiting LIN28 could be promising in treatment of cancer. Our experiments also demonstrate that MG132, a proteasome inhibitor, inhibits LIN28 expression and modulates expression of LIN28 mRNA targets in breast cancer cells. Studies are ongoing to reveal the mechanisms by which LIN28 regulates bound targets and how proteasome inhibitors impact this regulation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4192. doi:1538-7445.AM2012-4192

Inhibition of Let-7 Processing in Adult Murine Hematopoietic Stem Cells Induces a Fetal-Like High Self-Renewal Pattern in Their Progeny

Abstract 45Fetal hematopoietic stem cells (HSCs) in mice differ from their adult counterparts in a number of key properties. These include a higher cycling activity, an ability to more rapidly reconstitute the HSC compartment of irradiated recipient mice, a higher output of myeloid as compared to lymphoid progeny, and a greater sensitivity to the self-renewal promoting activity of Steel factor. We have previously shown that most of these features of fetal HSCs are sustained until 3 weeks after birth at which time they are rapidly (within 1 week), completely and permanently replaced with the corresponding properties of adult HSCs. A candidate regulator of this transition, Hmga2, was identified based on its greater expression in highly purified fetal versus adult HSCs (CD45+EPCR+CD48−CD150+; E-SLAM cells) with persistence of this difference in the matching lineage-negative (lin−) compartments. Experiments in which Hmga2 was overexpressed by lentiviral transduction of purified adult HSCs which were then transplanted into irradiated mice provided evidence that this chromatin remodeling factor can activate a fetal-like HSC program in these cells; i.e., more rapidly reconstitute the HSC compartment (increased self-renewal response) and produce clones with a higher proportion of myeloid cells. Based on the known ability of the let-7 family of microRNAs (miRNAs) to target Hmga2 transcripts resulting in their degradation and/or translational repression, we next hypothesized that let-7 miRNAs might be involved in controlling HSC developmental programs. A comparison of the levels of expression of 6 members of the let-7 family in purified fetal and adult HSCs, as well as in lin− hematopoietic cells, showed that transcripts for all of these are higher in the adult subsets, although this difference was significant only for let-7b (p<0.05). Since Lin28 is a natural inhibitor of let-7 miRNA biogenesis we proposed that overexpression of this protein might be used to simultaneously inhibit all let-7 miRNA species and therefore modulate let-7-mediated effects in HSCs. Transduction of BA/F3 cells with a Lin28-YFP lentiviral vector led to an elevated expression of Lin28 and a significant decrease in multiple let-7 miRNAs. To investigate the influence of Lin28 overexpression on adult HSC self-renewal activity in vivo, we used the same Lin28 lentiviral vector (or a control YFP vector) to transduce highly purified HSCs (40 E-SLAM cells, i.e. ∼20 HSCs/group/experiment, 3 experiments) in a 3–4-hour exposure protocol and then transplanted all of the cells directly into irradiated mice (total of 3–4 mice/group). The number of HSCs regenerated 6 weeks later was subsequently measured by performing limiting-dilution transplants in secondary mice (total of 12–16 secondary mice/group/experiment). Interestingly, analysis of the secondary recipients showed that the Lin28-overexpressing adult HSCs had expanded in the primary recipients ∼6-fold more than the control-virus transduced HSCs (p<0.001). These findings support our thesis that alterations in let-7 miRNA levels play a key role in regulating the developmental switch from fetal to adult HSCs programs that occurs between 3 and 4 weeks after birth in mice. Disclosures:No relevant conflicts of interest to declare.

NANOG priming before full reprogramming may generate germ cell tumours

Reprogramming somatic cells into a pluripotent state brings patient-tailored, ethical controversy-free cellular therapy closer to reality. However, stem cells and cancer cells share many common characteristics; therefore, it is crucial to be able to discriminate between them. We generated two induced pluripotent stem cell (iPSC) lines, with NANOG pre-transduction followed by OCT3/4, SOX2, and LIN28 overexpression. One of the cell lines, CHiPS W, showed normal pluripotent stem cell characteristics, while the other, CHiPS A, though expressing pluripotency markers, failed to differentiate and gave rise to germ cell-like tumours in vivo. Comparative genomic hybridisation analysis of the generated iPS lines revealed that they were genetically more stable than human embryonic stem cell counterparts. This analysis proved to be predictive for the differentiation potential of analysed cells. Moreover, the CHiPS A line expressed a lower ratio of p53/p21 when compared to CHiPS W. NANOG pre-induction followed by OCT3/4, SOX2, MYC, and KLF4 induction resulted in the same tumour-inducing phenotype. These results underline the importance of a re-examination of the role of NANOG during reprogramming. Moreover, this reprogramming method may provide insights into primordial cell tumour formation and cancer stem cell transformation.

Lin28-let7-Blimp1 Circuitry regulates human primordial germ cells (hPGC) development from human embryonic stem cells (hESC)

Lin28-let7-Blimp1 Circuitry regulates human primordial germ cells (hPGC) development from human embryonic stem cells (hESC)

Abstract 3082: Exploring LIN28 mRNA targets in breast cancer cells

Abstract LIN28 is a RNA binding protein and a pluripotency factor. It represses tumor suppressing microRNA let-7 and thus derepresses let-7 oncogene targets such as HMGA2, K-Ras and c-Myc. In addition, LIN28 binds and enhances translation of IGF-2 mRNA a known mitogen. Recent reports show that LIN28 overexpression promotes tumor cell migration and cellular transformation through repression of let-7, and that overexpression is associated with advanced stages of disease, including breast cancer. Despite the apparent critical role in cancer, the molecular function and mode of action of LIN28 is not yet elucidated. To further understand the function of LIN28, we explored LIN28 mRNA targets in breast cancer cells using RNA-protein immunoprecipitation (RIP-Chip) followed by RNA sequencing. Using RIP-Chip and RNA sequencing we have identified a number of novel LIN28 targets in MCF-7 breast cancer cells. Therapeutic drugs inhibiting LIN28 could be promising in treatment of cancer. Our experiments also demonstrate that MG132, a proteasome inhibitor, inhibits LIN28 expression and modulates expression of LIN28 mRNA targets in breast cancer cells. The mechanism by which LIN28 regulates its targets is unknown; however, a number of the new targets are important in cancer. Previous studies suggest that LIN28 acts through translational mechanisms. Studies are ongoing to reveal the mechanisms by which LIN28 regulates bound targets and how proteasome inhibitors impact this regulation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3082. doi:10.1158/1538-7445.AM2011-3082