Triple-negative breast cancer (TNBC) is a subtype of breast cancer that lacks expression of estrogen receptor, progesterone receptor, and the HER2 but is enriched with cancer stem celllike cells (CSC). CSCs are the fraction of cancer cells recognized as the source of primary malignant tumors that also give rise to metastatic recurrence. 5-Hydroxymethylcytosine (5hmC) is a DNA epigenetic feature derived from 5-methylcytosine by action of tet methylcytosine dioxygenase enzymes (e.g., TET1); and although TET1 and 5hmC are required to maintain embryonic stem cells, the mechanism and role in CSCs remain unknown. Data presented in this report support the conclusion that TET1 and TET1-dependent 5hmC mediate hydrogen peroxide (H 2 O 2 )-dependent activation of a novel gene expression cascade driving self-renewal and expansion of CSCs in TNBC. Evidence presented also supports that the H 2 O 2 affecting this pathway arises due to endogenous mechanismsincluding downregulation of antioxidant enzyme catalase in TNBC cells-and by exogenous routes, such as systemic inflammation and oxidative stress coupled with obesity, a known risk factor for TNBC incidence and recurrence.Implications: This study elucidates a pathway dependent on H 2 O 2 and linked to obesity-driven TNBC tumor-initiating CSCs; thus, it provides new understanding that may advance TNBC prevention and treatment strategies.

Obesity is a risk factor for triple‐negative breast cancer ( TNBC ) incidence and poor outcomes, but the underlying molecular biology remains unknown. We previously identified in TNBC cell cultures that expression of epigenetic reader methyl‐CpG‐binding domain protein 2 ( MBD 2), specifically the alternative mRNA splicing variant MBD variant 2 ( MBD 2_v2), is dependent on reactive oxygen species ( ROS ) and is crucial for maintenance and expansion of cancer stem cell‐like cells ( CSC s). Because obesity is coupled with inflammation and ROS , we hypothesized that obesity can fuel an increase in MBD 2_v2 expression to promote the tumor‐initiating CSC phenotype in TNBC cells in vivo . Analysis of TNBC patient datasets revealed associations between high tumor MBD 2_v2 expression and high relapse rates and high body mass index ( BMI ). Stable gene knockdown/overexpression methods were applied to TNBC cell lines to elucidate that MBD 2_v2 expression is governed by ROS ‐dependent expression of serine‐ and arginine‐rich splicing factor 2 ( SRSF 2). We employed a diet‐induced obesity ( DIO ) mouse model that mimics human obesity to investigate whether obesity causes increased MBD 2_v2 expression and increased tumor initiation capacity in inoculated TNBC cell lines. MBD 2_v2 and SRSF 2 levels were increased in TNBC cell line‐derived tumors that formed more frequently in DIO mice relative to tumors in lean control mice. Stable MBD 2_v2 overexpression increased the CSC fraction in culture and increased TNBC cell line tumor initiation capacity in vivo . SRSF 2 knockdown resulted in decreased MBD 2_v2 expression, decreased CSC s in TNBC cell cultures, and hindered tumor formation in vivo . This report describes evidence to support the conclusion that MBD 2_v2 expression is induced by obesity and drives TNBC cell tumorigenicity, and thus provides molecular insights into support of the epidemiological evidence that obesity is a risk factor for TNBC . The majority of TNBC patients are obese and rising obesity rates threaten to further increase the burden of obesity‐linked cancers, which reinforces the relevance of this report.

African American men (AAM) are at higher risk of being diagnosed with prostate cancer (PCa) and are at higher risk of dying from the disease compared to European American men (EAM). We sought to better understand PCa molecular diversity that may be underlying these disparities. We performed RNA‐sequencing analysis on high‐grade PCa to identify genes showing differential tumor versus noncancer adjacent tissue expression patterns unique to AAM or EAM. We observed that interleukin‐6 (IL‐6) was upregulated in the nonmalignant adjacent tissue in AAM, but in EAM IL‐6 expression was higher in PCa tissue. Enrichment analysis identified that genes linked to the function of TP53 were overrepresented and downregulated in PCa tissue from AAM. These RNA‐sequencing results informed our subsequent investigation of a diverse PCa cell line panel. We observed that PCa cell lines that are TP53 wild‐type, which includes cell lines derived from AAM (MDA‐PCa‐2b and RC77T), did not express detectable IL‐6 mRNA. IL‐6 treatment of these cells downregulated wild‐type TP53 protein and induced mRNA and protein expression of the epigenetic reader methyl CpG binding domain protein 2 (MBD2), specifically the alternative mRNA splicing variant MBD2_v2. Further investigation validated that upregulation of this short isoform promotes self‐renewal and expansion of PCa cancer stem‐like cells (CSCs). In conclusion, this report contributes to characterizing gene expression patterns in high‐grade PCa and adjacent noncancer tissues from EAM and AAM. The results we describe here advance what is known about the biology associated with PCa race disparities and the molecular signaling of CSCs.