Our previous work revealed that rhomboid domain-containing protein 1 (RHBDD1) participates in the modulation of cell growth and apoptosis in colorectal cancer cells. This study aimed to investigate the function of RHBDD1 in regulating breast cancer progression and its underlying molecular basis. Immunohistochemistry was performed to evaluate RHBDD1 expression in 116 breast cancer tissue and 39 adjacent normal tissue and expression of RHBDD1, phospho-Akt (p-Akt) and cyclin-dependent kinase 2 (CDK2) in the same 84 breast cancer specimens. RHBDD1-knock-out cells were established using breast cancer cell lines. In vitro studies were carried out to estimate the function of RHBDD1 in cell proliferation, migration and invasion. Fluorescence microscopy assay and flow cytometric analysis were used to measure apoptosis and cell cycle regulation. RNA sequencing and western blot analysis were used to investigate the molecular mechanisms of RHBDD1. RHBDD1 was highly up-regulated in breast cancer tissue compared with that in normal tissue and associated with pathological tumor (pT) stage, pathological tumor-node-metastasis (pTNM) stage and estrogen receptor (ER) expression. RHBDD1 up-regulation was associated with poor prognosis in several subtypes of breast cancer. Deletion of RHBDD1 promoted apoptosis and suppressed proliferation, migration and invasion in breast cancer cells. RHBDD1 deletion suppressed Akt activation and decreased CDK2 protein level via proteasome pathway, thus inhibited cell cycle progression and G1/S phase transition. Moreover, the protein level of RHBDD1, p-Akt and CDK2 was significantly positively correlated in breast cancer tissue. Our study reveals that RHBDD1 promotes breast cancer progression by regulating p-Akt and CDK2 protein levels, and might be a potential biomarker and prognostic indicator for breast cancer patients.

Background. Basal‐like breast cancer (BLBC) exhibits worse pathological features than other breast cancer subtypes, and patients diagnosed with BLBC have short disease‐free and overall survival times. Thus, the identification of novel biomarkers and therapeutic targets for BLBC is of upmost importance. Although TPD52L2 is upregulated in multiple cancers, little is known about its roles in BLBC. Methods. RNA levels were analyzed between breast cancer tissues and paired adjacent normal tissues using RNA‐seq data from The Cancer Genome Atlas (TCGA). TPD52L2 stable knockdown and inducible knockout cell lines were established using basal‐like MDA‐MB‐231 and MDA‐MB‐453 cell lines. Cell proliferation assays in vitro and tumor growth analysis in vivo were performed to determine the function of TPD52L2 during BLBC progression. Transwell assays were used to estimate the regulatory effect of TPD52L2 on BLBC cell migration. The expression profile of all tpd52l2 transcripts was analyzed to assess the functional protein isoform. Association of transcript variant 6 (V6) expression with pathological parameters was carried out using the clinical data of the BRCA cohort. Results. We identified V6 of TPD52L2 as a novel biomarker and regulator of BLBC progression. TPD52L2 is upregulated in BLBCs and associated with patient outcomes. TPD52L2 knockdown suppresses tumor growth, and V6 correlates with cancer‐related phenotypes in BLBC. Clinical data further proved that V6 is associated with different pathological features, such as pathological stage and pathological tumor status, and independently predicts patient outcomes and responses to therapies. Conclusions. Our findings demonstrate that V6 of TPD52L2 is a novel biomarker for BLBC patients. V6 promotes cell proliferation and migration and has marked oncogenic roles in determining the malignant phenotypes of BLBC.

This study aimed to explore the regulatory role of sterol regulatory element‐binding protein 1 (SREBP1) in the antioxidant enzyme B166 and to examine the prognostic and therapeutic potential of B166 in glioblastoma multiforme (GBM). RNA‐seq data from TCGA and GTEX databases were analyzed to explore the relationship between B166 and GBM, as well as between B166 and SREBP1. Functional experiments were performed to determine whether SREBPs could regulate B166 expression level and to identify the major regulator of B166. Immunofluorescence staining was performed to investigate the cellular distribution of B166 in GBM. Quantitative reverse transcription polymerase chain reaction was employed to determine the regulatory effects of SREBP1‐a. CellROX Deep Red dye was applied to detect mitochondrial reactive oxygen species (ROS) levels. The results revealed that B166 protein was significantly upregulated in GBM tissues compared with lower‐grade gliomas and normal brain tissues ( p <0.0001). The B166 expression level was elevated through SREBP1‐a‐mediated regulation in GBM, simultaneously decreasing endogenous ROS levels to maintain cellular redox homeostasis and preserve normal mitochondrial function. Reducing SREBP1 level decreased both RNA and protein expression levels of B166. Overexpression of the active form of SREBP1‐a elevated the protein levels of B166 in both the mitochondria and nucleus. Pharmacological suppression of SREBP1 or genetic inhibition of B166 disrupted redox homeostasis, resulting in elevated oxidative stress and rapid cell death. In conclusion, B166 may serve as a promising therapeutic target for GBM. Its overexpression could enhance ROS elimination, highlighting its potential therapeutic benefits for GBM patients.