The Two-Hit Hypothesis Meets Epigenetics

Programmed cell death factor 4-mediated hippocampal synaptic plasticity is involved in early life stress and susceptibility to depression

Early life stress (ELS) increases the risk of depression later in life. Programmed cell death factor 4 (PDCD4), an apoptosis-related molecule, extensively participates in tumorigenesis and inflammatory diseases. However, its involvement in a person's susceptibility to ELS-related depression is unknown. To examine the effects and underlying mechanisms of PDCD4 on ELS vulnerability, we used a "two-hit" stress mouse model: an intraperitoneal injection of lipopolysaccharide (LPS) into neonatal mice was performed on postnatal days 7-9 (P7-P9) and inescapable foot shock (IFS) administration in adolescent was used as a later-life challenge. Our study shows that compared with mice that were only exposed to the LPS or IFS, the "two-hit" stress mice developed more severe depression/anxiety-like behaviors and social disability. We detected the levels of PDCD4 in the hippocampus of adolescent mice and found that they were significantly increased in "two-hit" stress mice. The results of immunohistochemical staining and Sholl analysis showed that the number of microglia in the hippocampus of "two-hit" stress mice significantly increased, with morphological changes, shortened branches, and decreased numbers. However, knocking down PDCD4 can prevent the number and morphological changes of microglia induced by ELS. In addition, we confirmed through the Golgi staining and immunohistochemical staining results that knocking down PDCD4 can ameliorate ELS-induced synaptic plasticity damage. Mechanically, the knockdown of PDCD4 exerts neuroprotective effects, possibly via the mediation of BDNF/AKT/CREB signaling. Combined, these results suggest that PDCD4 may play an important role in the ELS-induced susceptibility to depression and, thus, may become a therapeutic target for depressive disorders.

Wakefield M. The role of aberrant DNA methylation in cancer initiation and clinical impacts

Epigenetic alterations, including aberrant DNA methylation, are now recognized as bone fide hallmarks of cancer, which can contribute to cancer initiation, progression, therapy responses and therapy resistance. Methylation of gene promoters can have a range of impacts on cancer risk, clinical stratification and therapeutic outcomes. We provide several important examples of genes, which can be silenced or activated by promoter methylation and highlight their clinical implications. These include the mismatch DNA repair genes MLH1 and MSH2, homologous recombination DNA repair genes BRCA1 and RAD51C, the TERT oncogene and genes within the P15/P16/RB1/E2F tumour suppressor axis. We also discuss how these methylation changes might occur in the first place - whether in the context of the CpG island methylator phenotype or constitutional DNA methylation. The choice of assay used to measure methylation can have a significant impact on interpretation of methylation states, and some examples where this can influence clinical decision-making are presented. Aberrant DNA methylation patterns in circulating tumour DNA (ctDNA) are also showing great promise in the context of non-invasive cancer detection and monitoring using liquid biopsies; however, caution must be taken in interpreting these results in cases where constitutional methylation may be present. Thus, this review aims to provide researchers and clinicians with a comprehensive summary of this broad, but important subject, illustrating the potentials and pitfalls of assessing aberrant DNA methylation in cancer.

High tumor mutation burden (TMB) in microsatellite stable (MSS) colorectal cancers: Diverse molecular associations point to variable pathophysiology

BACKGROUND

Colorectal cancers with defects in the Mismatch Repair (MMR) system represent a minority of the disease. MMR defective cancers are characterized by high Tumor Mutation Burden (TMB) and are sensitive to immunotherapy with immune checkpoint inhibitors. In contrast, the majority of colorectal cancers are MMR proficient (Microsatellite Stable, MSS) and display a low TMB. However, a few of these MSS cancers have high TMB.

METHODS

Published genomic studies of colorectal cancers were examined to identify cases profiled as MSS and having a TMB above 10 mutations / Mb. Data from four studies detailed in the cBioportal for cancer genomics site and providing data on MSI status were examined.

RESULTS

In the MSK study of metastatic colorectal cancers, 7.5% of patients with MSS tumors had a high TMB of more than 10 mutations/ Mb. The MSK study of localized rectal cancers showed that 9.5% of patients with MSS tumors had a high TMB. The DFCI cohort included 10 patients with TMB above 10 mutations/ Mb characterized as MSS and not having MMR or proofreading polymerases mutations. Mutations in genes encoding for proteins of the KRAS pathways were more frequent in MSS tumors with high TMB than in counterparts with low TMB. Moreover, genes involved in DNA damage response and in epigenetic regulations were more frequently mutated in MSS colorectal cancers with high TMB.

CONCLUSION

Alterations of the KRAS signal transduction pathways, DDR gene mutations and epigenetic modifier mutations may contribute to increase mutation burden in subsets of MSS colorectal cancers.

Altered local RAS in the liver increased the risk of NAFLD in male mouse offspring produced by in vitro fertilization

BACKGROUND

Assisted reproductive technology (ART) is associated with an increased risk of adverse metabolic health in offspring, and these findings have been demonstrated in animal models without parental infertility issues. However, it is unclear what changes lead to abnormal metabolism. The activation of the renin-angiotensin system (RAS) has been related to various aspects of metabolic syndrome. Thus, we focused on the local RAS of the liver, which is the central organ for glucose and lipid metabolism in offspring conceived by in vitro fertilization (IVF), and studied the role of local liver RAS in metabolic diseases.

METHODS

Male C57BL/6 mouse offspring obtained by natural pregnancy and IVF were fed a standard chow diet or a high-fat diet (HFD) from 4 weeks of age through 16 weeks of age. We assessed glucose and lipid metabolism, hepatic histopathology, and the gene and protein expression of key RAS components. In addition, the blocker losartan was used from 4 weeks of age through 16 weeks of age to investigate the regulatory mechanisms of abnormal local RAS on metabolic activity in the IVF offspring liver.

RESULTS

The growth trajectories of IVF offspring body and liver weights were different from those of naturally pregnant offspring. Impaired glucose tolerance (IGT) and insulin resistance (IR) occurred in IVF-conceived male offspring. After continuous HFD feeding, male offspring in the IVF group underwent earlier and more severe IR. Furthermore, there was a trend of lipid accumulation in the livers of chow-fed IVF offspring. Hepatic steatosis was also more serious in the IVF offspring after HFD treatment. Type 1 receptor (AT1R), which is the primary receptor mediating the action of angiotensin (Ang) II, has been confirmed to be upregulated in IVF offspring livers. Losartan reduced or even eliminated most of the significant differences between the IVF and NC groups after HFD consumption.

CONCLUSIONS

The upregulation of AT1R expression in the liver increased the activity of the local RAS, resulting in abnormal glucose and lipid metabolism and lipid accumulation in the liver, significantly increasing the risk of nonalcoholic fatty liver disease (NAFLD) in IVF offspring.

Effect of Gene 33/Mig6/ERRFI1 on hexavalent chromium-induced transformation of human bronchial epithelial cells depends on the length of exposure

Hexavalent chromium (Cr(VI)) compounds are environmental and occupational lung carcinogens. The present study followed the chronic effect of Cr(VI) on the neoplastic transformation of BEAS-2B lung bronchial epithelial cells with or without deletion of Gene 33 (Mig6, EFFRI1), a multifunctional adaptor protein. We find that Gene 33-deleted cells exhibit increased anchorage-independent growth compared to control cells after transformed by 8-week but not 24-week Cr(VI) exposure. Gene 33-deleted cells show a higher level of cell proliferation and are more resistant to acute Cr(VI) toxicity compared to control cells after transformed by 8-week but not 24-week Cr(VI) exposure, despite that 24-week-transformed cells have increased resistance to acute Cr(VI) toxicity. However, Gene 33-deleted cells show increased migration after transformed by both 8-week and 24-week Cr(VI) exposures. Furthermore, only cells transformed by 24 weeks of Cr(VI) exposure can form subcutaneous tumors in nude mice. Although no significant difference in the size of tumors formed by the two cell types, there is a marked difference in the histological manifestation and more MMP3 expression in tumors from Gene 33-deleted cells. Our results demonstrate progressive neoplastic transformation of BEAS-2B cells and the adaptation of these cells to Gene 33 deletion during chronic exposure to Cr(VI).

HTLV-1 persistent infection and ATLL oncogenesis

Human T-cell leukemia virus type 1 (HTLV-1) is an oncogenic retrovirus; whereas HTLV-1 mainly persists in the infected host cell as a provirus, it also causes a malignancy called adult T-cell leukemia/lymphoma (ATLL) in about 5% of infection. HTLV-1 replication is in most cases silent in vivo and viral de novo infection rarely occurs; HTLV-1 rather relies on clonal proliferation of infected T cells for viral propagation as it multiplies the number of the provirus copies. It is mechanistically elusive how leukemic clones emerge during the course of HTLV-1 infection in vivo and eventually cause the onset of ATLL. This review summarizes our current understanding of HTLV-1 persistence and oncogenesis, with the incorporation of recent cutting-edge discoveries obtained by high-throughput sequencing.