High Dietary Iron in Western Diet-Fed Male Rats Causes Pancreatic Islet Injury and Acute Pancreatitis.

BACKGROUND: High dietary iron has been linked to an increased type 2 diabetes risk. We have previously shown that intrauterine growth restriction (IUGR) and feeding a Western diet (WD) to male Sprague-Dawley rats independently, as well as together, cause pancreatic islet inflammation, fibrosis, and hemosiderosis. OBJECTIVES: To investigate whether iron has a role in the pathogenesis of this inflammatory islet injury caused by IUGR and WD intake. METHODS: Male Sprague-Dawley offspring of bilateral uterine artery ligated (IUGR) and sham-operated (Sham) dams, fostered to nonoperated dams, were fed a WD [45% sucrose, 19.4% protein and 23% fat (w/w)] containing low iron (LI, 20 mg/kg) or high iron (HI, 500 mg/kg) from weaning. Four groups were studied: Sham-LI, Sham-HI, IUGR-LI, and IUGR-HI. Serial measurements of rat body weight, blood glucose, lipids and insulin, an intraperitoneal glucose tolerance test (age 13 wk), and histological analysis of pancreas and liver (age 14 wk) were recorded. The effects of iron, IUGR, and their interaction, on these measurements have been analyzed. RESULTS: WD with HI compared with LI caused an 11% greater weight gain by age 14 wk (P < 0.001), impaired glucose tolerance [AUC for glucose (G-AUC) 17% higher; P < 0.001), acute pancreatitis (17/18, HI; 6/17, LI; P < 0.001), pancreas-associated fat necrosis and saponification (7/18, HI; 0/17 LI; P < 0.01), and a trend to islet fibrotic injury (7/18, HI; 1/17 LI; P = 0.051). Although pancreatic and hepatic steatosis was evident in almost all WD-fed rats, pancreatic and hepatic iron accumulation was prevalent only in HI-fed rats (P < 0.0001 for both), being only mild in the livers. IUGR, independent of dietary iron, also caused impairment in glucose tolerance (G-AUC: 17% higher; P < 0.05). CONCLUSIONS: A postweaning WD containing HI, independent of IUGR, causes acute pancreatitis and islet injury in Sprague-Dawley rats suggesting a role of dietary iron in the development of steatopancreatitis.

H2A.B is a cancer/testis factor involved in the activation of ribosome biogenesis in Hodgkin lymphoma.

Testis-specific regulators of chromatin function are commonly ectopically expressed in human cancers, but their roles are poorly understood. Examination of 81 primary Hodgkin lymphoma (HL) samples showed that the ectopic expression of the eutherian testis-specific histone variant H2A.B is an inherent feature of HL. In experiments using two HL cell lines derived from different subtypes of HL, H2A.B knockdown inhibited cell proliferation. H2A.B was enriched in both nucleoli of these HL cell lines and primary HL samples. We found that H2A.B enhanced ribosomal DNA (rDNA) transcription, was enriched at the rDNA promoter and transcribed regions, and interacted with RNA Pol I. Depletion of H2A.B caused the loss of RNA Pol I from rDNA chromatin. Remarkably, H2A.B was also required for high levels of ribosomal protein gene expression being located at the transcriptional start site and within the gene body. H2A.B knockdown reduced gene body chromatin accessibility of active RNA Pol II genes concurrent with a decrease in transcription. Taken together, our data show that in HL H2A.B has acquired a new function, the ability to increase ribosome biogenesis.

Normative values of renin and aldosterone in clinically stable preterm neonates.

BACKGROUND: There is a paucity of literature on the normative levels of plasma renin concentration (PRC) and serum aldosterone (SA) in premature neonates. This study aims to provide normative data on PRC and SA levels in preterm neonates in the first 2 weeks after birth and explore associations with maternal, perinatal, or postnatal factors. METHODS: Neonates born at 26- to 34-week gestation were recruited from two neonatal intensive care units in Canada and Australia. The direct renin assay PRC and SA were analyzed on day 1 and days 14-21 after birth to compare across categorical variables and to produce normative values. RESULTS: A total of 262 subjects were enrolled from the Canadian (29%) and Australian (71%) sites. The mean gestational age was 30 weeks, with a mean birth weight of 1457 g. The normative values of PRC and SA for neonates born between 26 + 0 and 29 + 6 weeks and 30 + 0 and 34 + 0 weeks of gestation were produced for day 1 and day 14-21 after birth. Both PRC and SA increased from day 1 to day 14-21. The more premature neonates reached a higher PRC on days 14-21 after birth but exhibited lower SA levels on day 1 after birth. When comparing gender, birth weight, and maternal risk factor categories, no statistical differences in PRC or SA were found. A small but significant decrease in PRC, but not SA, was noted for neonates with placental pathology. CONCLUSIONS: This study produced normative values of PRA and SA in clinically stable preterm neonates that can be referenced for use in clinical practice. A higher resolution version of the Graphical abstract is available as Supplementary information.

Validation of a tool for determining the clinical utility of stillbirth investigations.

BACKGROUND: Up to 20% of all stillbirths and 45% of term stillbirths are currently classified as unexplained. Many of these stillbirths do not undergo currently recommended investigations. This may leave questions unanswered and not identify stillbirths with a recurrence risk in subsequent pregnancies. AIMS: To validate a new tool (Stillbirth Investigation Utility Tool) to identify the clinical utility of investigations in stillbirth and the inter-rater agreement on cause of stillbirth using the Perinatal Society of Australia and New Zealand-Perinatal Death Classification (PSANZ-PDC). MATERIALS AND METHODS: Thirty-four stillbirths were randomly selected for inclusion, each assessed independently by five blinded assessors. The investigations were grouped into three categories: clinical and laboratory; placental pathology; and autopsy examination. The cause of death was assigned at the end of each group. Outcome measures were clinical utility of investigations measured by assessor rated usefulness and inter-rater agreement on the assigned cause of death. RESULTS: Comprehensive maternal history, maternal full blood count, maternal blood group and screen and placenta histopathology were useful in all cases. Clinical photographs were not performed and should have been performed in 50% of cases. The inter-rater agreement on cause of death assigned after all investigation results was 0.93 (95% CI 0.87-1.0). CONCLUSIONS: The new Stillbirth Investigation Utility Tool showed very good agreement in assigning the cause of death using PSANZ-PDC. Four investigations were useful in all cases. Minor refinements will be made based on feedback to enhance usability for wider implementation in research studies to assess the yield of investigations in stillbirths.

Glutathione transferase Omega 1 confers protection against azoxymethane-induced colorectal tumour formation.

Inflammatory bowel disease (IBD) is characterized by multiple alterations in cytokine expression and is a risk factor for colon cancer. The Omega class glutathione transferase GSTO1-1 regulates the release of the pro-inflammatory cytokines interleukin 1ß (IL-1ß) and interleukin 18 (IL-18) by deglutathionylating NEK7 in the NLRP3 inflammasome. When treated with azoxymethane and dextran sodium sulphate (AOM/DSS) as a model of IBD, Gsto1-/- mice were highly sensitive to colitis and showed a significant increase in the size and number of colon tumours compared with wild-type (WT) mice. Gsto1-/- mice treated with AOM/DSS had significantly lower serum IL-1ß and IL-18 levels as well as significantly decreased interferon (IFN)-γ, decreased pSTAT1 and increased pSTAT3 levels in the distal colon compared with similarly treated WT mice. Histologically, AOM/DSS treated Gsto1-/- mice showed increased active chronic inflammation with macrophage infiltration, epithelial dysplasia and invasive adenocarcinoma compared with AOM/DSS treated WT mice. Thus, this study shows that GSTO1-1 regulates IL-1ß and IL-18 activation and protects against colorectal cancer formation in the AOM/DSS model of IBD. The data suggest that while GSTO1-1 is a new target for the regulation of the NLRP3 inflammasome-associated cytokines IL-1ß and IL-18 by small molecule inhibitors, there is a possibility that anti-inflammatory drugs targeting these cytokines may potentiate colon cancer in some situations.

Molecular patterns in salivary duct carcinoma identify prognostic subgroups.

Salivary duct carcinoma (SDCa) is a rare cancer with high rate of metastases and poor survival despite aggressive multimodality treatment. This study analyzes the genetic changes in SDCa, their impact on cancer pathways, and evaluates whether molecular patterns can identify subgroups with distinct clinical characteristics and outcome. Clinicopathologic details and tissue samples from 66 patients (48 males, 18 females) treated between 1995 and 2018 were obtained from multiple institutions. Androgen receptor (AR) was assessed by immunohistochemistry, and the Illumina TruSight 170 gene panel was used for DNA sequencing. Male gender, lympho-vascular invasion, lymph node metastasis, and smoking were significant predictors of disease-free survival. AR was present in 79%. Frequently encountered alterations were mutations in TP53 (51%), PIK3CA (32%) and HRAS (22%), as well as amplifications of CDK4/6 (22%), ERBB2 (21%), MYC (16%), and deletions of CDKN2A (13%). TP53 mutation and MYC amplifications were associated with decreased disease-free survival. Analysis of cancer pathways revealed that the PI3K pathway was most commonly affected. Alterations in the cell cycle pathway were associated with impaired disease-free survival (HR 2.6, P = 0.038). Three subgroups based on AR and ERBB2 status were identified, which featured distinct molecular patterns and outcome. Among AR positive SDCa, HRAS mutations were restricted to AR positive tumors without ERBB2 amplification and HRAS mutations featured high co-occurrence with PIK3CA alterations, which seems specific to SDCa. AR negative SDCa were associated with poor disease-free survival in multivariate analysis (HR 4.5, P = 0.010) and none of these tumors exhibited ERBB2 amplification or HRAS mutations. AR and ERBB2 status in SDCa thus classifies tumors with distinct molecular profiles relevant to future targeted therapy. Furthermore, clinical factors such as smoking and molecular features such as MYC amplification may serve as markers of poor prognosis of SDCa.

A pilot randomised clinical trial of 670 nm red light for reducing retinopathy of prematurity.

BACKGROUND: Photobiomodulation by 670 nm red light in animal models reduced severity of ROP and improved survival. This pilot randomised controlled trial aimed to provide data on 670 nm red light exposure for prevention of ROP and survival for a larger randomised trial. METHODS: Neonates <30 weeks gestation or <1150 g at birth were randomised to receive 670 nm for 15 min (9 J/cm2) daily until 34 weeks corrected age. DATA COLLECTED: placental pathology, growth, days of respiratory support and oxygen, bronchopulmonary dysplasia, patent ductus arteriosus, necrotising enterocolitis, sepsis, worst stage of ROP, need for laser treatment, and survival. RESULTS: Eighty-six neonates enrolled-45 no red light; 41 red light. There was no difference in severity of ROP (<27 weeks-p = 0.463; ≥27 weeks-p = 0.558) or requirement for laser treatment (<27 weeks-p = 1.00; ≥27 weeks-no laser treatment in either group). Survival in 670 nm red light treatment group was 100% (41/41) vs 89% (40/45) in untreated infants (p = 0.057). CONCLUSION: Randomisation to receive 670 nm red light within 24-48 h after birth is feasible. Although no improvement in ROP or survivability was observed, further testing into the dosage and delivery for this potential therapy are required.

IL-2 Enhances Gut Homing Potential of Human Naive Regulatory T Cells Early in Life.

Recent evidence suggests early environmental factors are important for gut immune tolerance. Although the role of regulatory T (Treg) cells for gut immune homeostasis is well established, the development and tissue homing characteristics of Treg cells in children have not been studied in detail. In this article, we studied the development and homing characteristics of human peripheral blood Treg cell subsets and potential mechanisms inducing homing molecule expression in healthy children. We found contrasting patterns of circulating Treg cell gut and skin tropism, with abundant ß7 integrin+ Treg cells at birth and increasing cutaneous lymphocyte Ag (CLA+) Treg cells later in life. ß7 integrin+ Treg cells were predominantly naive, suggesting acquisition of Treg cell gut tropism early in development. In vitro, IL-7 enhanced gut homing but reduced skin homing molecule expression in conventional T cells, whereas IL-2 induced a similar effect only in Treg cells. This effect was more pronounced in cord compared with adult blood. Our results suggest that early in life, naive Treg cells may be driven for gut tropism by their increased sensitivity to IL-2-induced ß7 integrin upregulation, implicating a potential role of IL-2 in gut immune tolerance during this critical period of development.

Uncertainty over implications of placental histopathological findings: A survey of Australian and New Zealand neonatologists.

AIM: Placental examination is known to provide useful information following an adverse pregnancy outcome. Despite existing literature and guidelines for placental examination; current workplace practices, attitudes towards the value of placental examination and the knowledge of perinatal clinicians regarding placental lesions of significance are unknown. The aim of the study is to explore the current knowledge of neonatologists and maternal fetal medicine specialists on placental histopathological findings and clinical management based on placental pathology. METHODS: A total of 280 specialists working in perinatal centres across Australia and New Zealand were invited to complete a 20-question online multiple-choice-based survey addressing work-place placental examination practices, and participant beliefs regarding the utility of histopathological findings and follow-up practices. RESULTS: A total of 74 neonatologists participated in the survey (28.2% response rate). Maternal fetal medicine specialists were excluded due to low response rate (2%). A total of 100% of respondents believed placental examination provided useful information regarding recent pregnancy and neonatal outcomes. They reported being aware of the presence of protocols for macroscopic examination of, and indications for histopathological examination of the placenta (55.4 and 54.1%, respectively). Nine neonatologists reported a system for actioning abnormal placental reports. There was no consensus amongst neonatologists as to which specific placental lesions held implications for future pregnancy or neonatal outcomes, and how these findings should be followed. CONCLUSIONS: Our findings show placental examination is valued amongst neonatologists in Australia and New Zealand, but highlights the need for better education regarding the significance and utility of the results and what would be best practice for following up reports.

A practical guide to placental examination for forensic pathologists.

The placenta is a complex interface organ that may hold clues to the reasons for fetal, neonatal or maternal demise. For this reason, placental examination should be a mandatory part of all perinatal or maternal autopsies. While published protocols for the examination of the placenta exist, they are often not adopted. The following review provides practical guidelines for placental examination, with discussion of specific medical conditions that can negatively impact upon the fetus, neonate or mother involving placental pathology to cause death. The review aims to discuss concepts, with illustrations, that forensic pathologists may not routinely focus on in death investigations that may either contribute or mask the cause of a fetal or neonatal death, or are associated with a recurrence risk. While it is recognized that many forensic facilities do not have formal guidelines for placental examination, involvement of local perinatal pathology services in cases is one way of obtaining additional specialist expertise.

Publisher Correction: A practical guide to placental examination for forensic pathologists.

The Publisher would like to correct the introduced formatting errors caused by production on figures 16 and 23 of the original article. The errors are purely typesetting mistakes and the corrections made to the figures did not impact upon the veracity and content of the overall text of the article in any way.

Placental histopathology in preterm fetal growth restriction.

AIMS: Approximately 6-9% pregnancies are affected by fetal growth restriction (FGR). Placental alterations related to utero-placental insufficiency in FGR may induce placental vascular remodelling to the detriment of the fetus. The objective of this article was to study histopathological features of placentae in a cohort of preterm growth-restricted infants in comparison to a cohort of preterm appropriately grown infants. METHODS: In a cohort of 40 preterm infants of 28-32 weeks' gestation, placental histopathology was evaluated by a histopathologist, who was blinded to the identity of the grouping. Twenty infants had FGR, while 20 were appropriate for gestational age (AGA). Predefined histopathological characteristics were assessed based on the Amsterdam Placental Workshop Group Consensus Statement. RESULTS: The gestational age and birthweight of the FGR and AGA cohorts were 29.8 ± 1.3 versus 30 ± 0.9 weeks, P = 0.78 and 923 ± 168 versus 1403 ± 237 g, <0.001, respectively. Maternal vascular malperfusion, accelerated villous maturation and fetal vascular malperfusion were features that were significantly more common in FGR placentae. CONCLUSION: Based on the results of the present study, specific placental histopathological changes may be present in FGR placentae, which may reflect the effects of utero-placental insufficiency.

Recurrent Chronic Intervillositis: The Diagnostic Challenge - A Case Report and Review of the Literature.

BACKGROUND: Chronic intervillositis (CI) is a rare placental condition involving diffuse infiltration of intervillous spaces by CD68- or CD45-positive maternal mononuclear inflammatory cells. Because no validated clinical or biochemical markers are specific to CI, the diagnosis is purely histopathological and is made postpartum. CASE: This report describes a case of recurrent CI associated with adverse complications in two successive pregnancies. Both pregnancies were complicated by intrauterine growth restriction. Coexistent massive perivillous fibrin deposition was present in the first placenta. This case highlights the importance of CI in explaining and predicting adverse perinatal outcomes. CONCLUSION: CI is associated with adverse pregnancy outcomes and a high risk of recurrence, and it can coexist with massive perivillous fibrin deposition. Pathologists must ensure that the significance of these diagnoses is adequately conveyed to clinicians, to optimize management of subsequent pregnancies.

Nuclear-Biased DUSP6 Expression is Associated with Cancer Spreading Including Brain Metastasis in Triple-Negative Breast Cancer.

DUSP6 is a dual-specificity phosphatase (DUSP) involved in breast cancer progression, recurrence, and metastasis. DUSP6 is predominantly cytoplasmic in HER2+ primary breast cancer cells, but the expression and subcellular localization of DUSPs, especially DUSP6, in HER2-positive circulating tumor cells (CTCs) is unknown. Here we used the DEPArray system to identify and isolate CTCs from metastatic triple negative breast cancer (TNBC) patients and performed single-cell NanoString analysis to quantify cancer pathway gene expression in HER2-positive and HER2-negative CTC populations. All TNBC patients contained HER2-positive CTCs. HER2-positive CTCs were associated with increased ERK1/ERK2 expression, which are direct DUSP6 targets. DUSP6 protein expression was predominantly nuclear in breast CTCs and the brain metastases but not pleura or lung metastases of TNBC patients. Therefore, nuclear DUSP6 may play a role in the association with cancer spreading in TNBC patients, including brain metastasis.

Optimizing poly (ADP-ribose) polymerase inhibition through combined epigenetic and immunotherapy.

Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype with poor survival outcomes. Currently, there are no targeted therapies available for TNBCs despite remarkable progress in targeted and immune-directed therapies for other solid organ malignancies. Poly (ADP-ribose) polymerase inhibitors (PARPi) are effective anticancer drugs that produce good initial clinical responses, especially in homologous recombination DNA repair-deficient cancers. However, resistance is the rule rather than the exception, and recurrent tumors tend to have an aggressive phenotype associated with poor survival. Many efforts have been made to overcome PARPi resistance, mostly by targeting genes and effector proteins participating in homologous recombination that are overexpressed during PARPi therapy. Due to many known and unknown compensatory pathways, genes, and effector proteins, overlap and shared resistance are common. Overexpression of programmed cell death-ligand 1 (PD-L1) and cancer stem cell (CSC) sparing are novel PARPi resistance hypotheses. Although adding programmed cell death-1 (PD-1)/PD-L1 inhibitors to PARPi might improve immunogenic cell death and be crucial for durable responses, they are less likely to target the CSC population that drives recurrent tumor growth. Lysine-specific histone demethylase-1A and histone deacetylase inhibitors have shown promising activity against CSCs. Combining epigenetic drugs such as lysine-specific histone demethylase-1A inhibitors or histone deacetylase inhibitors with PARPi/anti-PD-1/PD-L1 is a novel, potentially synergistic strategy for priming tumors and overcoming resistance. Furthermore, such an approach could pave the way for the identification of new upstream epigenetic and genetic signatures.

Dichloroacetate Prevents Cisplatin-Induced Nephrotoxicity without Compromising Cisplatin Anticancer Properties.

Cisplatin is an effective anticancer drug; however, cisplatin use often leads to nephrotoxicity, which limits its clinical effectiveness. In this study, we determined the effect of dichloroacetate, a novel anticancer agent, in a mouse model of cisplatin-induced AKI. Pretreatment with dichloroacetate significantly attenuated the cisplatin-induced increase in BUN and serum creatinine levels, renal tubular apoptosis, and oxidative stress. Additionally, pretreatment with dichloroacetate accelerated tubular regeneration after cisplatin-induced renal damage. Whole transcriptome sequencing revealed that dichloroacetate prevented mitochondrial dysfunction and preserved the energy-generating capacity of the kidneys by preventing the cisplatin-induced downregulation of fatty acid and glucose oxidation, and of genes involved in the Krebs cycle and oxidative phosphorylation. Notably, dichloroacetate did not interfere with the anticancer activity of cisplatin in vivo. These data provide strong evidence that dichloroacetate preserves renal function when used in conjunction with cisplatin.

Islet inflammation, hemosiderosis, and fibrosis in intrauterine growth-restricted and high fat-fed Sprague-Dawley rats.

Prenatal and postnatal factors such as intrauterine growth restriction (IUGR) and high-fat (HF) diet contribute to type 2 diabetes. Our aim was to determine whether IUGR and HF diets interact in type 2 diabetes pathogenesis, with particular attention focused on pancreatic islet morphology including assessment for inflammation. A surgical model of IUGR (bilateral uterine artery ligation) in Sprague-Dawley rats with sham controls was used. Pups were fed either HF or chow diets after weaning. Serial measures of body weight and glucose tolerance were performed. At 25 weeks of age, rat pancreases were harvested for histologic assessment. The birth weight of IUGR pups was 13% lower than that of sham pups. HF diet caused excess weight gain, dyslipidemia, hyperinsulinemia, and mild glucose intolerance, however, this was not aggravated further by IUGR. Markedly abnormal islet morphology was evident in 0 of 6 sham-chow, 5 of 8 sham-HF, 4 of 8 IUGR-chow, and 8 of 9 IUGR-HF rats (chi-square, P = 0.007). Abnormal islets were characterized by larger size, irregular shape, inflammation with CD68-positive cells, marked fibrosis, and hemosiderosis. ß-Cell mass was not altered by IUGR. In conclusion, HF and IUGR independently contribute to islet injury characterized by inflammation, hemosiderosis, and fibrosis. This suggests that both HF and IUGR can induce islet injury via converging pathways. The potential pathogenic or permissive role of iron in this process of islet inflammation warrants further investigation.

The effect of pregnancy-induced hypertensive disorders on placental growth along short and long axes and neonatal outcomes.

AIM: To assess the effect of pregnancy-induced hypertensive disorders on the growth of the placenta on the short and long axes and neonatal outcomes. MATERIALS AND METHODS: A retrospective cohort study of gross and histological characteristics of placentas and the fetal outcomes of normotensive and hypertensive pregnancies over a three-year period from January 2009 to December 2011 at a tertiary teaching hospital in ACT, Australia. RESULTS: Placentas and neonatal outcomes from 100 pregnancies complicated with pregnancy-induced hypertension/pre-eclampsia were studied and compared with 51 gestational age-matched placentas and neonatal outcomes from normotensive pregnancies. The median maternal age and smoking history were similar in the two groups (P = 0.894; P = 1.00, respectively). The median pre-pregnancy weight was significantly higher (P < 0.001) and primiparity more common (P = 0.001) in the study group. The median weight of the placenta was significantly lower (P < 0.001) and below the 10th centile (P < 0.001) in the study group. Both the long and short axes of the placental disc were significantly smaller in the study group (P = 0.002; P ≤ 0.001 respectively). Accelerated villous maturation, placental infarcts and decidual vessel vasculopathy were more common in the study group (P < 0.001). The median birthweight and the number of infants with birthweight and length below the 10th centile were significantly higher in the study group (P = 0.008; P < 0.001; P = 0.004, respectively). CONCLUSION: This study demonstrates that pregnancy-induced hypertension significantly influences the growth and development of both the placenta and fetus.

Inhibition of LINE-1 retrotransposon-encoded reverse transcriptase modulates the expression of cell differentiation genes in breast cancer cells.

Long Interspersed Elements (L1 elements) are biologically active retrotransposons that are capable of autonomous replication using their own reverse transcriptase (RT) enzyme. Expression of the normally repressed RT has been implicated in cancer cell growth. However, at present, little is known about the expression of L1-encoded RT activity or the molecular changes that are associated with RT activity in the development of breast cancer. Here, we report that RT activity is widespread in breast cancer cells. The expression of RT protein decreased markedly in breast cancer cells after treatment with the antiretroviral drug, efavirenz. While the majority of cells showed a significant reduction in proliferation, inhibition of RT was also accompanied by cell-specific differences in morphology. MCF7 cells displayed elongated microtubule extensions that adhered tightly to their substrate, while a large fraction of the T47D cells that we studied formed long filopodia projections. These morphological changes were reversible upon cessation of RT inhibition, confirming their dependence on RT activity. We also carried out gene expression profiling with microarrays and determined the genes that were differentially expressed during the process of cellular differentiation. Genes involved in proliferation, cell migration, and invasive activity were repressed in RT-inhibited cells. Concomitantly, genes involved in cell projection, formation of vacuolar membranes, and cell-to-cell junctions were significantly upregulated in RT-inhibited cells. qRT-PCR examination of the mRNA expression of these genes in additional cell lines yielded close correlation between their differential expression and the degree of cellular differentiation. Our study demonstrates that the inhibition of L1-encoded RT can reduce the rate of proliferation and promote differentiation of breast cancer cells. Together, these results provide a direct functional link between the expression of L1 retrotransposons and the development of breast cancer.