[Endogenous retroviruses: friend or foe of the immune system?]

Correlation of SARS‑CoV‑2 to cancer: Carcinogenic or anticancer? (Review)

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is highly infectious and pathogenic. Among patients with severe SARS-CoV-2-caused by corona virus disease 2019 (COVID-19), those complicated with malignant tumor are vulnerable to COVID-19 due to compromised immune function caused by tumor depletion, malnutrition and anti-tumor treatment. Cancer is closely related to the risk of severe illness and mortality in patients with COVID-19. SARS-CoV-2 could promote tumor progression and stimulate metabolism switching in tumor cells to initiate tumor metabolic modes with higher productivity efficiency, such as glycolysis, for facilitating the massive replication of SARS-CoV-2. However, it has been shown that infection with SARS-CoV-2 leads to a delay in tumor progression of patients with natural killer cell (NK cell) lymphoma and Hodgkin's lymphoma, while SARS-CoV-2 elicited anti-tumor immune response may exert a potential oncolytic role in lymphoma patients. The present review briefly summarized potential carcinogenicity and oncolytic characteristics of SARS-CoV-2 as well as strategies to protect patients with cancer during the COVID-19 pandemic.

Bivalent Regulation and Related Mechanisms of H3K4/27/9me3 in Stem Cells

The "bivalent domain" is a unique histone modification region consisting of two histone tri-methylation modifications. Over the years, it has been revealed that the maintenance and dynamic changes of the bivalent domains play a vital regulatory role in the differentiation of various stem cell systems, as well as in other cells, such as immunomodulation. Tri-methylation modifications involved in the formation of the bivalent domains are interrelated and mutually regulated, thus regulating many life processes of cells. Tri-methylation of histone H3 at lysine 4 (H3K4me3), tri-methylation of histone H3 at lysine 9 (H3K9me3) and tri-methylation of histone H3 at lysine 27 (H3K27me3) are the main tri-methylation modifications involved in the formation of bivalent domains. The three form different bivalent domains in pairs. Furthermore, it is equally clear that H3K4me3 is a positive regulator of transcription and that H3K9me3/H3K27me3 are negative regulators. Enzymes related to the regulation of histone methylation play a significant role in the "homeostasis" and "breaking homeostasis" of the bivalent domains. Bivalent domains regulate target genes, upstream transcription, downstream targeting regulation and related cytokines during the establishment and breakdown of homeostasis, and exert the specific regulation of stem cells. Indeed, a unified mechanism to explain the bivalent modification in all stem cells has been difficult to define, and whether the bivalent modification is antagonistic in inducing the differentiation of homologous stem cells is controversial. In this review, we focus on the different bivalent modifications in several key stem cells and explore the main mechanisms and effects of these modifications involved. Finally, we discussed the close relationship between bivalent domains and immune cells, and put forward the prospect of the application of bivalent domains in the field of stem cells.