LINE-1 retrotransposition events affect endothelial proliferation and migration

Role Of Retroelements In The Development Of COVID-19 Neurological Consequences

Retroelements play a key role in brain functioning in humans and other animals, since they represent dynamic regulatory elements controlling the expression of specific neuron types. The activity of retroelements in the brain is impaired under the influence of SARS-CoV-2, penetrating the blood-brain barrier. We propose a new concept, according to which the neurological complications of COVID-19 and their long-term effects are caused by modified expression of retroelements in neurons due to viral effect. This effect is implemented in several ways: a direct effect of the virus on the promoter regions of retroelement-encoding genes, virus interaction with miRNAs causing silencing of transposons, and an effect of the viral RNA on the products of retroelement transcription. Aging-related physiological activation of retroelements in the elderly is responsible for more severe course of COVID-19. The associations of multiple sclerosis, Parkinson’s disease, Guillain-Barré syndrome, acute disseminated encephalomyelitis with coronavirus lesions also indicate the role of retroelements in such complications, because retroelements are involved in the mechanisms of the development of these diseases. According to meta-analyses, COVID-19-caused neurological complications ranged 36.4-73%. The neuropsychiatric consequences of COVID-19 are observed in patients over a long period after recovery, and their prevalence may exceed those during the acute phase of the disease. Even 12 months after recovery, unmotivated fatigue, headache, mental disorders, and neurocognitive impairment were observed in 82%, 60%, 26.2-45%, and 16.2-46.8% of patients, correspondingly. These manifestations are explained by the role of retroelements in the integration of SARS-CoV-2 into the human genome using their reverse transcriptase and endonuclease, which results in a long-term viral persistence. The research on the role of specific retroelements in these changes can become the basis for developing targeted therapy for neurological consequences of COVID-19 using miRNAs, since epigenetic changes in the functioning of the genome in neurons, affected by transposons, are reversible.

mRNA Vaccines: Why Is the Biology of Retroposition Ignored?

The major advantage of mRNA vaccines over more conventional approaches is their potential for rapid development and large-scale deployment in pandemic situations. In the current COVID-19 crisis, two mRNA COVID-19 vaccines have been conditionally approved and broadly applied, while others are still in clinical trials. However, there is no previous experience with the use of mRNA vaccines on a large scale in the general population. This warrants a careful evaluation of mRNA vaccine safety properties by considering all available knowledge about mRNA molecular biology and evolution. Here, I discuss the pervasive claim that mRNA-based vaccines cannot alter genomes. Surprisingly, this notion is widely stated in the mRNA vaccine literature but never supported by referencing any primary scientific papers that would specifically address this question. This discrepancy becomes even more puzzling if one considers previous work on the molecular and evolutionary aspects of retroposition in murine and human populations that clearly documents the frequent integration of mRNA molecules into genomes, including clinical contexts. By performing basic comparisons, I show that the sequence features of mRNA vaccines meet all known requirements for retroposition using L1 elements-the most abundant autonomously active retrotransposons in the human genome. In fact, many factors associated with mRNA vaccines increase the possibility of their L1-mediated retroposition. I conclude that is unfounded to a priori assume that mRNA-based therapeutics do not impact genomes and that the route to genome integration of vaccine mRNAs via endogenous L1 retroelements is easily conceivable. This implies that we urgently need experimental studies that would rigorously test for the potential retroposition of vaccine mRNAs. At present, the insertional mutagenesis safety of mRNA-based vaccines should be considered unresolved.

Ductal cells of minor salivary glands in Sjögren's syndrome express LINE-1 ORF2p and APOBEC3B

BACKGROUND

Type I interferon activation is a hallmark event in Sjögren's syndrome. L1 retroelements stimulate plasmacytoid dendritic cells, activating the type I interferons, and are regulated by various mechanisms, including the APOBEC3 deaminases. As L1s are potential trigger factors in autoimmunity, we aimed to investigate the immunohistochemical localization of L1 ORF2p and its inhibitor APOBEC3B protein in minor salivary glands of Sjögren's syndrome patients.

METHODS

Twenty minor salivary gland-tissue samples from 20 Sjögren's syndrome patients, classified according to Tarpley's histological criteria, and 10 controls were evaluated for L1 ORF2p and APOBEC3B expression via immunohistochemistry.

RESULTS

L1 ORF2p was expressed in 17/20 SS patients and all controls. APOBEC3B expression was observed in 15/20 Sjögren's syndrome patients, 5/5 chronic sialadenitis, and 3/5 normal minor salivary glands. Both antibodies stained the cytoplasm of the ductal epithelial cells. Negative staining was observed in the acinar cells. L1 ORF2p-positive immunostaining was significantly lower in Tarpley IV Sjögren's syndrome patients than controls (P = .039), and APOBEC3B-positive staining was significantly lower in Tarpley I compared to Tarpley II Sjögren's syndrome patients (P = .008) and controls (P = .035).

CONCLUSIONS

L1 ORF2p and APOBEC3B are expressed in the ductal epithelial cells of minor salivary glands that are among the key targets in Sjögren's syndrome. L1 ORF2p expression may promote the L1 ability to act as an intrinsic antigen in Sjögren's syndrome. The potential future use of L1 ORF2-reverse transcriptase inhibitors in autoimmunity supports further investigation of L1 epigenetic regulation by APOBEC3 enzymes.

Distinct subcellular localization and potential role of LINE1-ORF1P in meiotic oocytes

LINE-1 is an autonomous non-LTR retrotransposon in mammalian genomes and encodes ORF1P and ORF2P. ORF2P has been clearly identified as the enzyme supplier needed in LINE-1 retrotransposition. However, the role of ORF1P is not well explored. In this study, we employed loss/gain-of-function approach to investigate the role of LINE1-ORF1P in mouse oocyte meiotic maturation. During mouse oocyte development, ORF1P was observed in cytoplasm as well as in nucleus at germinal vesicle (GV) stage while was localized on the spindle after germinal vesicle breakdown (GVBD). Depletion of ORF1P caused oocyte arrest at the GV stage as well as down-regulation of CDC2 and CYCLIN B1, components of the maturation-promoting factor (MPF). Further analysis demonstrated ORF1P depletion triggered DNA damage response and most of the oocytes presented altered chromatin configuration. In addition, SMAD4 showed nuclear foci signal after Orf1p dsRNA injection. ORF1P overexpression held the oocyte development at MI stage and the chromosome alignment and spindle organization were severely affected. We also found that ORF1P could form DCP1A body-like foci structure in both cytoplasm and nucleus after heat shock. Taken together, accurate regulation of ORF1P plays an essential role in mouse oocyte meiotic maturation.

Expression of a LINE-1 endonuclease variant in gastric cancer: its association with clinicopathological parameters

Background

Long interspersed nuclear element-1 (LINE-1 or L1), the most abundant and only autonomously active family of non-LTR retrotransposons in the human genome, expressed not only in the germ lines but also in somatic tissues. It contributes to genetic instability, aging, and age-related diseases, such as cancer. Our previous study identified in human gastric adenocarcinoma an upregulated transcript GCRG213, which shared 88% homology with human L1 sequence and contained a putative conserved apurinic/apyrimidinic endonucleas1 domain.

Methods

Immunohistochemistry was carried out by using a monoclonal mouse anti-human GCRG213 protein (GCRG213p) antibody produced in our laboratory, on tissue microarray constructed with specimens from 175 gastric adenocarcinoma patients. The correlation between GCRG213p expression and patient clinicopathological parameters was evaluated. GCRG213p expression in gastric cancer cell lines were studied using Western blotting analysis. L1 promoter methylation status of gastric cancer cells was tested using methylation-specific PCR. BLASTP was used at the NCBI Blast server to identify GCRG213p sequence to any alignments in the Protein Data Bank databases.

Results

Most primary gastric cancer, lymph node metastases and gastric intestinal metaplasia glands showed positive GCRG213p immunoreactivity. High GCRG213p immunostaining score in the primary gastric cancer was positively correlated with tumor differentiation (well differentiated, p = 0.001), Lauren’s classification (intestinal type, p < 0.05) and a late age onset of gastric adenocarcinoma (≥65 yrs; p < 0.05). GCRG213p expression has no association with other clinicopathological parameters, including survival. Western blotting analysis of GCRG213p expression in gastric cancer cells indicated that GCRG213p level was higher in gastric cancer cell lines than in human normal gastric epithelium immortalized cell line GES-1. Partial methylation of L1 in gastric cancer cells was confirmed by methylation-specific PCR. BLASTP program analysis revealed that GCRG213p peptide shared 83.0% alignment with the C-terminal region of L1 endonuclease (L1-EN). GCRG213p sequence possesses the important residues that compose the conserved features of L1-EN.

Conclusions

GCRG213p could be a variant of L1-EN, a functional member of L1-EN family. Overexpression of GCRG213p is common in both primary gastric cancer and lymph node metastasis. These findings provide evidence of somatic L1 expression in gastric cancer, and its potential consequences in the form of tumor.

Prognostic value of LINE-1 retrotransposon expression and its subcellular localization in breast cancer

Long interspersed nuclear element 1 (L1) belongs to a family of retrotransposons. Expression of the normally repressed L1 retrotransposons has been shown to induce genome instability by creating DNA double-stranded breaks and chromosomal rearrangements through the process of retrotransposition. At present, little is known about the expression of L1-encoded ORF1p and ORF2p which are indispensable for its retrotransposition activity. Given its potentially harmful effects on the genome, we investigated the implications of both ORF1p and ORF2p expression and their subcellular localization in a range of breast cancer cell lines and breast tumor tissues including 15 normal breast tissues, 25 fibroadenomas, 25 ductal carcinomas in situ (DCIS), and 95 invasive cancers. Clinicopathologic parameters and survival outcomes were investigated in association with the cytoplasmic and nuclear expression of ORF1p and ORF2p using univariate and multivariate analysis. High cytoplasmic expression of ORF1p and ORF2p was seen in DCIS tumors, but they were not related with survival outcome. The majority of invasive cancers were found to express both ORF1p and ORF2p in the cytoplasm, while nuclear expression was also seen in a subclass of those invasive cancers in the range of 28–31 %. Tumors with high nuclear expression of ORF1p and ORF2p were more significantly associated with lymph node metastasis (p = 0.001) and the worst patient survival (p < 0.0001) than those with cytoplasmic expression. This is the first study examining the effects of both ORF1p and ORF2p expression in breast cancer tissues. Our observation shows altered expression patterns of ORF1p and ORF2p within invasive cancers, which are related to differences in overall patient survival. The differing patterns of both cytoplasmic and nuclear ORF1p and ORF2p expression indicate that further studies of the biology and function of L1 retrotransposons are required in breast cancer.

LINE-1 retrotransposition events regulate gene expression after X-ray irradiation

Long interspersed nuclear element-1 (LINE-1) retrotransposons are mobile elements that insert into new genomic locations via reverse transcription of an RNA intermediate. The mechanism of retrotransposition is not entirely understood. The integration of these elements occurs by target-primed reverse transcription (TPRT), which initiates double-strand breaks (DSBs) during the LINE-1 integration. Also, X-ray is known to induce DNA damage. The aim of this study was to evaluate the potential effects of LINE-1 de novo retrotransposition on the expression of different genes after X-ray irradiation in human endothelial cells. After stable transfection of the human hybrid endothelial cell line EA.hy926 with the human LINE-1 element, we analyzed the expression of different genes after irradiation with 5 Gy X-rays by reverse transcription-polymerase chain reaction (RT-PCR). We determine the expression level of phosphorylated p53 and γ-histone H2AX protein levels upon X-ray irradiation with 5 Gy for 24 h. Our results showed that EA.hy926 LINE-1 cell clones react with a strong upregulation of phosphorylated p53 protein, already 15 min after irradiation compared to the wild type (WT) cells. Also, the expression of γ-histone H2AX protein was elevated in the cell clones with retrotransposition events 15 min after irradiation, whereas the WT cells have a delayed expression of phosphorylated histone H2AX protein. Taken together, our findings provide that LINE-1 retrotransposition events regulate different gene expression after irradiation in the EA.hy926 cell line.

Histochemistry and cell biology: the annual review 2010

This review summarizes recent advances in histochemistry and cell biology which complement and extend our knowledge regarding various aspects of protein functions, cell and tissue biology, employing appropriate in vivo model systems in conjunction with established and novel approaches. In this context several non-expected results and discoveries were obtained which paved the way of research into new directions. Once the reader embarks on reading this review, it quickly becomes quite obvious that the studies contribute not only to a better understanding of fundamental biological processes but also provide use-oriented aspects that can be derived therefrom.