Human germ/stem cell-specific gene TEX19 influences cancer cell proliferation and cancer prognosis

TEX19 increases the levels of CDK4 and promotes breast cancer by disrupting SKP2-mediated CDK4 ubiquitination

BACKGROUND

Globally, breast cancer in women is the fifth leading cause of cancer death. There is an urgent need to explore the molecular mechanism of breast cancer proliferation and metastasis.

METHOD

TCGA database analysis was used to analyze genes expression in breast cancer and normal samples and the association between gene expression and prognosis. Immunohistochemical staining, qPCR and western blotting was sued to detected gene expression. The cell function tests were conducted to investigate the effects of TEX19 and CDK4 with abnormal expression on cell proliferation, migration, apoptosis, cell cycle, and colony formation. Bioinformatics analysis methods combined with CHX tracking experiment and Co-IP experiment were performed to screen and verify the downstream molecule and regulatory mechanism of TEX19. Besides, subcutaneous tumorigenesis model in nude mice was constructed.

RESULTS

TEX19 was significantly upregulated in breast cancer, and the TEX19 level was related to tumor invasion and prognosis. TEX19 knockdown inhibited the proliferation and migration of breast cancer cells, increased cell apoptosis, and blocked the cell cycle in the G2 phase. Besides, TEX19 suppressed the growth of tumors in the body. Mechanically, TEX19 upregulated the level of CDK4 protein, which depended on the E3 ubiquitin ligase SKP2. Specifically, TEX19 knockdown and SKP2 protein overexpression destroyed the stability of CDK4 protein and enhanced the ubiquitination of CDK4 protein. Additionally, CDK4 knockdown inhibited the proliferation, migration, and colony formation of breast cancer cells, and alleviated the promotion of TEX19 overexpression on the proliferation and migration of breast cancer cell.

CONCLUSION

TEX19 and CDK4 were upregulated in breast cancer, and TEX19 increased the level of CDK4 protein by influencing SKP2-mediated ubiquitination of CDK4, thereby promoting the progression of breast cancer.

Transcription Factor FOXA1 Facilitates Glycolysis and Proliferation of Lung Adenocarcinoma via Activation of TEX19

Glycolysis is a shared feature in various cancers including lung adenocarcinoma (LUAD). Testis Expressed 19 (TEX19) is correlated with cancer progression. But its effect on LUAD remains an unanswered question. The focus of our study was primarily to investigate how TEX19 works exactly in LUAD. We first downloaded mRNA data from TCGA-LUAD and performed differential expression analysis. Then, we performed a Kaplan-Meier analysis to analyze the relationship between mRNA expression and patients' prognoses. hTFtarget database was utilized for the prediction of upstream transcription factors of mRNA. Next, qRT-PCR was employed for detecting TEX19 and Forkhead box A1 (FOXA1) expression. Western blot was adopted to detect the expression of glycolysis-related proteins. We also used CCK-8, colony formation, and flow cytometry assays to detect cell viability, proliferation, and apoptosis. Seahorse XF Extracellular Flux Analyzers were introduced to analyze extracellular acidification rate (ECAR) and oxygen consumption rate (OCR). Detection kits were used to detect pyruvate, lactate, citric acid, and malic acid. TEX19 was highly expressed in LUAD tissues. Real-time quantitative PCR (qRT-PCR) assay showed that TEX19 was significantly overexpressed in LUAD cell lines compared with normal bronchial epithelial cells BEAS-2B. Knockdown of TEX19 remarkably inhibited cell activity and proliferation, and promoted cell apoptosis, TEX19 was enriched in the glycolytic pathway. Meanwhile, the knockdown of TEX19 significantly hampered the contents of pyruvate, lactate, citric acid, and malic acid. The bioinformatics analysis, dual luciferase reporter experiment, and chromatin immunoprecipitation (ChIP) assay showed that FOXA1 was bound with TEX19. FOXA1 had a high expression level in LUAD. The rescue assay demonstrated that FOXA1, by activating TEX19 expression, enhanced glycolysis and proliferation and inhibited apoptosis of LUAD cells. In summary, FOXA1 promoted glycolysis and proliferation of LUAD cells by activating TEX19. This result can provide a theoretical basis for future research on LUAD.

Characterization of the m6A regulator-mediated methylation modification patterns in oral squamous cell carcinoma

N⁶-methyladenosine (m⁶A) is a form of posttranscriptional modification that plays important roles in cancer including oral squamous cell carcinoma (OSCC). Most studies to date have focused on a limited number of regulators and oncogenic pathways, thus failing to provide comprehensive insight into the dynamic effects of m⁶A modification. In addition, the role of m⁶A modification in shaping immune cell infiltration in OSCC has yet to be clarified. This study was designed to assess m⁶A modification dynamics in OSCC and to understand how such modifications influence clinical immunotherapeutic treatment outcomes. m⁶A modification patterns linked with 23 m⁶A regulators were analyzed in 437 OSCC patients from TCGA and GEO cohorts. These patterns were then quantified through m⁶A score based on algorithms derived from a principal component analysis (PCA) approach. The m⁶A modification patterns of OSCC samples were grouped into two clusters based on the m⁶A regulators expression, and immune cell infiltration was linked with the 5-year survival outcomes of patients in these clusters. 1575 genes associated with OSCC patient prognosis were identified and used to re-cluster these samples into two groups. Patients in clusters exhibiting higher levels of m⁶A regulator expression exhibited poorer overall survival (OS), whereas patients with high m⁶A scores survived for longer (p < 0.001). The overall mortality rates in the groups of patients with low and high m⁶A scores were 55% and 40%, respectively, and the m⁶A score distributions in clusters of patients grouped by m⁶A modification patterns and gene expression further supported the link between a high m⁶A score and better prognostic outcomes. Immunophenoscore (IPS) values for patients in different m⁶A score groups suggested that the use of PD-1-specific antibodies or CTLA-4 inhibitors alone or in combination would yield superior treatment outcomes in patients in the high-m⁶A score group relative to the low-m⁶A score group. m⁶A modification patterns are relevant to heterogeneity in OSCC. Detailed analyses of m⁶A modification patterns may thus offer novel insight regarding immune cell infiltration within the OSCC tumor microenvironment, guiding novel efforts to provide patients with more effective immunotherapeutic interventions.

The Transcriptome and Proteome Networks of Malignant Tumours Reveal Atavistic Attractors of Polyploidy-Related Asexual Reproduction

The expression of gametogenesis-related (GG) genes and proteins, as well as whole genome duplications (WGD), are the hallmarks of cancer related to poor prognosis. Currently, it is not clear if these hallmarks are random processes associated only with genome instability or are programmatically linked. Our goal was to elucidate this via a thorough bioinformatics analysis of 1474 GG genes in the context of WGD. We examined their association in protein-protein interaction and coexpression networks, and their phylostratigraphic profiles from publicly available patient tumour data. The results show that GG genes are upregulated in most WGD-enriched somatic cancers at the transcriptome level and reveal robust GG gene expression at the protein level, as well as the ability to associate into correlation networks and enrich the reproductive modules. GG gene phylostratigraphy displayed in WGD+ cancers an attractor of early eukaryotic origin for DNA recombination and meiosis, and one relative to oocyte maturation and embryogenesis from early multicellular organisms. The upregulation of cancer-testis genes emerging with mammalian placentation was also associated with WGD. In general, the results suggest the role of polyploidy for soma-germ transition accessing latent cancer attractors in the human genome network, which appear as pre-formed along the whole Evolution of Life.

Biomarkers of disease recurrence in stage I testicular germ cell tumours

Stage I testicular cancer is a disease restricted to the testicle. After orchiectomy, patients are considered to be without disease; however, the tumour is prone to relapse in ~4-50% of patients. Current predictive markers of relapse, which are tumour size and invasion to rete testis (in seminoma) or lymphovascular invasion (in non-seminoma), have limited clinical utility and are unable to correctly predict relapse in a substantial proportion of patients. Adjuvant therapeutic strategies based on available biomarkers can lead to overtreatment of 50-85% of patients. Discovery and implementation of novel biomarkers into treatment decision making will help to reduce the burden of adjuvant treatments and improve patient selection for adjuvant therapy.

Cancer testis antigens and genomic instability: More than immunology

Cancer testis antigens or genes (CTA, CTG) are predominantly expressed in adult testes while silenced in most or all somatic tissues with sporadic expression in many human cancers. Concerted misexpression of numerous CTA/CTGs is rarely observed. This finding argues against the germ cell theory of cancer. A surprising number of CTA/CTGs are involved in meiotic chromosome metabolism and specifically in meiotic recombination. Recent discoveries with a group of CTGs established that their misexpression in somatic cells results in genomic instability by interfering with homologous recombination (HR), a DNA repair pathway for complex DNA damage such as DNA double-stranded breaks, interstrand crosslinks, and single-stranded DNA gaps. HR-deficient tumors have specific vulnerabilities and show synthetic lethality with inhibition of polyADP-ribose polymerase, opening the possibility that expression of CTA/CTGs that result in an HR-defect could be used as an additional biomarker for HR status. Here, we review the repertoire of CTA/CTGs focusing on a cohort that functions in meiotic chromosome metabolism by interrogating relevant cancer databases and discussing recent discoveries.

In silico modeling of the interaction between TEX19 and LIRE1, and analysis of TEX19 gene missense SNPs

BACKGROUND

Testis expressed 19 (TEX19) is a specific human stem cell gene identified as cancer-testis antigen (CTA), which emerged as a potential therapeutic drug target. TEX19.1, a mouse paralog of human TEX19, can interact with LINE-1 retrotransposable element ORF1 protein (LIRE1) and subsequently restrict mobilization of LINE-1 elements in the genome.

AIM

This study aimed to predict the interaction of TEX19 with LIRE1 and analyze TEX19 missense polymorphisms. TEX19 model was generated using I-TASSER and the interaction between TEX19 and LIRE1 was studied using the HADDOCK software.

METHODS

The stability of the docking formed complex was studied through the molecular dynamic simulation using GROMACS. Missense SNPs (n=102) of TEX19 were screened for their potential effects on protein structure and function using different software.

RESULTS

Outcomes of this study revealed amino acids that potentially stabilize the predicted interaction interface between TEX19 and LIRE1. Of these SNPs, 37 were predicted to play a probably damaging role for the protein, three of them (F35S, P61R, and E55L) located at the binding site of LIRE1 and could disturb this binding affinity.

CONCLUSION

This information can be verified by further in vitro and in vivo experimentations and could be exploited for potential therapeutic targets.

Malignant Evaluation and Clinical Prognostic Values of M6A RNA Methylation Regulators in Prostate Cancer

Objective: M6A RNA modification is closely associated with tumor genesis and progression of several malignancies; however, its role in prostate cancer (PCa) remains poorly understood.

Materials and methods: Expression data and corresponding clinicopathologic information were available freely from the Cancer Genome Atlas (TCGA) dataset. We compared the expression level of m6A RNA methylation regulators in PCa with different clinicopathologic characteristics and identified subgroups based on their expressions with consensus clustering. To build the signature and assess its prognostic value, several methods were used for the analysis, including univariate Cox regression analysis, Least Absolute Shrinkage and Selection Operator (LASSO) regression analysis, time-dependent receiver operating curve (ROC), and Kaplan-Meier (KM) survival analysis.

Results: Most of the m6A RNA methylation regulators were differentially expressed not only between normal and tumor tissue but also among PCa stratified by different clinicopathologic characteristics. There were obvious differences between two clusters, cluster 1 and 2, regarding clinicopathologic features, and the recurrence-free survival (RFS) in cluster 2 was significantly worse than cluster 1. We developed an eleven-gene signature which exhibited a high prognostic value and was able to independently predict RFS. Moreover, a nomogram which integrated clinical information and the gene signature was capable of distinguishing high-risk recurrent patients.

Conclusion: These methylation regulators are correlated to clinicopathologic characteristics in PCa and a prognostic model using m6A methylation-related genes is constructed and of high predictive value for recurrence after RP.

Prediction of relapse in stage I testicular germ cell tumor patients on surveillance: investigation of biomarkers

Background

Better biomarkers for assessing risk of relapse in stage I testicular germ cell tumor patients are needed, to complement classical histopathological variables. We aimed to assess the prognostic value of previously suggested biomarkers, related to proliferation (MIB-1 and TEX19) and to immune microenvironment (CXCL12, CXCR4, beta-catenin and MECA-79) in a surveillance cohort of stage I testicular germ cell tumor patients.

Methods

A total of 70 patients were included. Survival analyses were performed, including Cox regression models.

Results

Patients with vascular invasion and elevated human chorionic gonadotropin levels showed significantly poorer relapse-free survival in multivariable analysis (hazard ratio = 2.820, 95% confidence interval 1.257–6.328; hazard ratio = 3.025, 95% confidence interval 1.345–6.808). Patients with no vascular invasion but with MIB-1 staining in > 50% tumor cells showed significantly shorter relapse-free survival (p = 0.042). TEX19 nuclear immunoexpression was confirmed in spermatogonial cells, and weak cytoplasmic immunoexpression was depicted in 15/70 tumors, not significantly impacting survival. CXCL12 immunoexpression in tumor cells did not associate with relapse, but non-seminoma patients exhibiting vascular invasion and CXCL12-positive stromal/inflammatory cells showed significantly improved relapse-free survival (p = 0.015). Exclusively nuclear immunoexpression of CXCR4 associated with better relapse-free survival (p = 0.032), but not after adjusting for vascular invasion. Patients with higher beta-catenin scores showed a tendency for poorer relapse-free survival (p = 0.056). MECA-79 immunoexpression was absent.

Conclusions

The informative protein biomarkers (i.e., MIB-1, CXCL12, beta-catenin, and possibly CXCR4) may prove useful for risk-stratifying patients if validated in larger, multicentric and well-defined studies. Currently, classical histopathological features of testicular germ cell tumors remain key for relapse prediction.

Tex19.1 inhibits the N-end rule pathway and maintains acetylated SMC3 cohesin and sister chromatid cohesion in oocytes

Age-dependent oocyte aneuploidy, a major cause of Down syndrome, is associated with declining sister chromatid cohesion in postnatal oocytes. Here we show that cohesion in postnatal mouse oocytes is regulated by Tex19.1. We show Tex19.1-/- oocytes have defects maintaining chiasmata, missegregate their chromosomes during meiosis, and transmit aneuploidies to the next generation. Furthermore, we show that mouse Tex19.1 inhibits N-end rule protein degradation mediated by its interacting partner UBR2, and that Ubr2 itself has a previously undescribed role in negatively regulating the acetylated SMC3 subpopulation of cohesin in mitotic somatic cells. Lastly, we show that acetylated SMC3 is associated with meiotic chromosome axes in mouse oocytes, and that this population of cohesin is specifically depleted in the absence of Tex19.1. These findings indicate that Tex19.1 regulates UBR protein activity to maintain acetylated SMC3 and sister chromatid cohesion in postnatal oocytes and prevent aneuploidy from arising in the female germline.

TEX19 promotes ovarian carcinoma progression and is a potential target for epitope vaccine immunotherapy

AIMS

Testis Expressed 19 (TEX19) is one of cancer/testis antigens identified in recent years and is related to the oncogenesis and progress of several cancers. This study aimed to reveal the role of TEX19 in ovarian cancer (OC) and searched for potential candidate epitope peptides of TEX19 to facilitate clinical application.

MAIN METHODS

TEX19 levels were evaluated by immunohistochemistry (IHC) in 98 human ovarian tissue samples. The correlation of TEX19 levels with patients' clinicopathological features was assessed. Quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting analysis were utilized to detect TEX19 levels in ovarian cell lines and TEX19-deficient cells. The level of TEX19 in OVCAR-3 and A2780 was knocked down by small interfering RNA (siRNA), and loss-of-function assays were used to determine the biological effects of TEX19 on the proliferation, migration, and invasion of OC cells. Subsequently, candidate epitope peptides from TEX19 were predicted and verified by the IEDB database, pepsite2 website, MOE software, and T2 cell binding assay.

KEY FINDINGS

TEX19 was significantly upregulated in OC which correlated to higher TNM stage, lymph node involvement, and invasiveness. Knockdown of TEX19 inhibited proliferation, migration, and invasion of OC cells. Additionally, we screened four peptides derived from TEX19 and found TL to be the dominant peptide with the greatest affinity with HLA-A*0201.

SIGNIFICANCE

Our data indicated a cancer-promoting effect of TEX19 in OC and demonstrated that TL could be a potential candidate for an anti-tumor epitope vaccine of OC, suggesting that TEX19 is a promising biomarker and immunotherapeutic target for OC.

Characterization of Hepatocellular Carcinoma Cell Lines Using a Fractionation-Then-Sequencing Approach Reveals Nuclear-Enriched HCC-Associated lncRNAs

Background: Advances in sequencing technologies have greatly improved our understanding of long noncoding RNA (lncRNA). These transcripts with lengths of >200 nucleotides may play significant regulatory roles in various biological processes. Importantly, the dysregulation of better characterized lncRNAs has been associated with multiple types of cancers, including hepatocellular carcinoma (HCC). There are many studies on altered lncRNA expression levels, very few, however, have focused on their subcellular localizations, from which accumulating evidences have indicated their close relationships to lncRNA functions. A transcriptome-wide investigation of the subcellular distributions of lncRNAs might thus provide new insights into their roles and functions in cancers.

Results: In this study, we subjected eight patient-derived HCC cell lines to subcellular fractionation and independently sequenced RNAs from the nuclear and cytoplasmic compartments. With the integration of tumor and tumor-adjacent RNA-seq datasets of liver hepatocellular carcinoma (LIHC) from The Cancer Genome Atlas (TCGA), de novo transcriptome assembly and differential expression analysis were conducted successively and identified 26 nuclear-enriched HCC-associated lncRNAs shared between the HCC samples and the TCGA datasets, including the reported cancer driver PXN-AS1. The majority of nuclear-enriched HCC-associated lncRNAs were associated with the survival outcomes of HCC patients, exhibited characteristics similar to those of many experimentally supported HCC prognostic lncRNAs, and were co-expressed with protein-coding genes that have been linked to disease progression in various cancer types.

Conclusion: We adopted a fractionation-then-sequencing approach on multiple patient-derived HCC samples and identified nuclear-enriched, HCC-associated lncRNAs that could serve as important targets for HCC diagnosis and therapeutic development. This approach could be widely applicable to other studies into the disease etiologies of lncRNA.

TEX9 and eIF3b functionally synergize to promote the progression of esophageal squamous cell carcinoma

Background

Esophageal squamous cell carcinoma (ESCC) is one of the most frequent malignant digestive tumors around the world. We previously demonstrated that eIF3b could promote the progression of ESCC. The exact mechanisms underlying these effects remained unknown.

Methods

Quantitative proteomics was applied to detect the potential targets of Eukaryotic translation initiation factor 3 subunit b (eIF3b). RT-qPCR and Western blot were performed to detect the expression of targeted gene and pathway related genes. RNA-immunoprecipitation was applied to verify the binding of eIF3b with targeted gene. Moreover, CCK-8 assay, colony-formation assay, transwell assay, flow cytometry for cell apoptosis and tumor xenograft assay were performed to analyze the regulation of the targeted gene on the bio-function of ESCC cells.

Results

Quantitative proteomics data showed that Testis-expressed protein 9 (TEX9) expression was positively associated with eIF3b expression. RT-qPCR and Western blot results confirmed the quantitative proteomics data and demonstrated that TEX9 expression was positively correlated with TNM stage in ESCC. Furtherly, RNA-immunoprecipitation confirmed that eIF3b binding to TEX9 mRNA. The bio-function related assay demonstrated that TEX9 and eIF3b functionally synergized to promote the proliferation and migration, and inhibited the apoptosis of ESCC cells. In the analysis of mechanism, we revealed that TEX9 and eIF3b promoted the progression of ESCC through the activation of AKT signaling pathway.

Conclusions

The synergized promoting role of TEX9 and eIF3b in the progression of ESCC may provide a novel mechanism for exploring viable therapeutic strategies for ESCC.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-6071-9) contains supplementary material, which is available to authorized users.

miRNA-mRNA Associated With Survival in Endometrial Cancer

Although various factors may contribute to its initiation and progression, the etiology and prognostic factors of endometrial carcinoma (EC) remains not fully understood. We sought to understand the role of changes in transcriptome during the progress of EC by exploring public datasets. The aberrant expression characteristics of EC based on RNA-Seq and miRNA-seq data from The Cancer Genome Atlas (TCGA) were analyzed. Kaplan-Meier analysis was performed to assess the relationship between differently expressed genes (DEGs) and patient survival. As a result, 320 out of 4,613 differently expressed mRNAs (DE mRNAs) and 68 out of 531 differently expressed miRNAs (DE miRNAs) with a significantly poorer survival were determined. We predicted eight paired DE miRNAs and DE mRNAs through TargetScan. Patients with three out of the eight paired low rate of miRNA/mRNA (miR-497/EMX1, miR-23c/DMBX1, and miR-670/KCNS1) expression had a significantly poorer survival. Furthermore, the simultaneous presence of these selected low miRNA/mRNA pairs occurred in most patients and resulted in a significantly poorer survival rate. Luciferase reporter assay identified that EMX1 was a direct target of miR-497. Both low expression of miR-497 and overexpression of EMX1 were significantly associated with more advanced clinicopathologic characteristics (stage, tumor status, grade, and histology) besides survival (all P values < 0.05). Multivariate analysis also demonstrated that miR-497 remained an independent prognostic variable for overall survival. In summary, we identified that a series of DE mRNAs and miRNAs, including eight paired DE miRNAs and mRNAs, were associated with survival in EC. Clinical evaluation of downregulated miR-497 and paired upregulated EMX1 confirmed the value of our prediction analysis. The simultaneous presence of low rate of these selected low miRNA/mRNA pairs (miR-497/EMX1, miR-23c/DMBX1, and miR-670/KCNS1) might have a better prediction value. Therefore, further studies are required to validate these findings.

Meiotic gene activation in somatic and germ cell tumours

Background

Germ cell tumours are uniquely associated with the gametogenic tissues of males and females. A feature of these cancers is that they can express genes that are normally tightly restricted to meiotic cells. This aberrant gene expression has been used as an indicator that these cancer cells are attempting a programmed germ line event, meiotic entry. However, work in non‐germ cell cancers has also indicated that meiotic genes can become aberrantly activated in a wide range of cancer types and indeed provide functions that serve as oncogenic drivers. Here, we review the activation of meiotic factors in cancers and explore commonalities between meiotic gene activation in germ cell and non‐germ cell cancers.

Objectives

The objectives of this review are to highlight key questions relating to meiotic gene activation in germ cell tumours and to offer possible interpretations as to the biological relevance in this unique cancer type.

Materials and Methods

PubMed and the GEPIA database were searched for papers in English and for cancer gene expression data, respectively.

Results

We provide a brief overview of meiotic progression, with a focus on the unique mechanisms of reductional chromosome segregation in meiosis I. We then offer detailed insight into the role of meiotic chromosome regulators in non‐germ cell cancers and extend this to provide an overview of how this might relate to germ cell tumours.

Conclusions

We propose that meiotic gene activation in germ cell tumours might not indicate an unscheduled attempt to enter a full meiotic programme. Rather, it might simply reflect either aberrant activation of a subset of meiotic genes, with little or no biological relevance, or aberrant activation of a subset of meiotic genes as positive tumour evolutionary/oncogenic drivers. These postulates provide the provocation for further studies in this emerging field.

Meiosis-like Functions in Oncogenesis: A New View of Cancer

Cancer cells have many abnormal characteristics enabling tumors to grow, spread, and avoid immunologic and therapeutic destruction. Central to this is the innate ability of populations of cancer cells to rapidly evolve. One feature of many cancers is that they activate genes that are normally associated with distinct developmental states, including germ cell-specific genes. This has historically led to the proposal that tumors take on embryonal characteristics, the so called embryonal theory of cancer. However, one group of germline genes, not directly associated with embryonic somatic tissue genesis, is the one that encodes the specific factors to drive the unique reductional chromosome segregation of meiosis I, which also results in chromosomal exchanges. Here, we propose that meiosis I-specific modulators of reductional segregation can contribute to oncogenic chromosome dynamics and that the embryonal theory for cancer cell growth/proliferation is overly simplistic, as meiotic factors are not a feature of most embryonic tissue development. We postulate that some meiotic chromosome-regulatory functions contribute to a soma-to-germline model for cancer, in which activation of germline (including meiosis) functions drive oncogenesis, and we extend this to propose that meiotic factors could be powerful sources of targets for therapeutics and biomonitoring in oncology. Cancer Res; 77(21); 5712-6. ©2017 AACR.

Mobilization of LINE-1 retrotransposons is restricted by Tex19.1 in mouse embryonic stem cells

Mobilization of retrotransposons to new genomic locations is a significant driver of mammalian genome evolution, but these mutagenic events can also cause genetic disorders. In humans, retrotransposon mobilization is mediated primarily by proteins encoded by LINE-1 (L1) retrotransposons, which mobilize in pluripotent cells early in development. Here we show that TEX19.1, which is induced by developmentally programmed DNA hypomethylation, can directly interact with the L1-encoded protein L1-ORF1p, stimulate its polyubiquitylation and degradation, and restrict L1 mobilization. We also show that TEX19.1 likely acts, at least in part, through promoting the activity of the E3 ubiquitin ligase UBR2 towards L1-ORF1p. Moreover, loss of Tex19.1 increases L1-ORF1p levels and L1 mobilization in pluripotent mouse embryonic stem cells, implying that Tex19.1 prevents de novo retrotransposition in the pluripotent phase of the germline cycle. These data show that post-translational regulation of L1 retrotransposons plays a key role in maintaining trans-generational genome stability in mammals.