BAP1-defficient breast cancer in a patient with BAP1 cancer syndrome

Regulation of Med1 protein by overexpression of BAP1 in breast cancer cells

Med1 binds to a nuclear receptor and regulates transcription. Elevated Med1 protein expression promotes cancer growth in hormone-dependent breast and prostate cancers. Med1 protein expression was investigated by deubiquitinating enzymes (DUBs) overexpression in breast cancer cell lines. Various DNA constructs of SRT-DUBs were overexpressed in the MCF7 cell line, and Med1 protein expression was investigated by western blotting. The cell growth and in vitro invasion assay were performed in BRCA1-associated protein 1 (BAP1) wild type and mutant (C91A) overexpressed cells. Ubiquitination of the Med1 protein was observed, and Med1 protein expression and transcriptional activity were verified by various DUBs overexpressed. Although Med1 protein expression increased upon the overexpression of BAP1, it was not affected by the overexpression of BAP1 mutant (C91A). BAP1 was increased by the E2 treatment, which has an important effect on the breast cancer growth, and cell growth was decreased by BAP1 C91A overexpression. However, metastatic capacities were decreased by BAP1. In addition, the binding between the Med1 and the BAP1 protein was observed. These data suggested that BAP1 regulated Med1 protein expression in breast cancer cells and involved in cancer cell growth and metastasis by binding to Med1 protein.

Functional assay for assessment of pathogenicity of BAP1 variants

BACKGROUND

Pathogenic germline variants in BRCA1-Associated Protein 1 (BAP1) cause BAP1 tumor predisposition syndrome (BAP1-TPDS). Carriers run especially a risk of uveal (UM) and cutaneous melanoma, malignant mesothelioma, and clear cell renal carcinoma. Approximately half of increasingly reported BAP1 variants lack accurate classification. Correct interpretation of pathogenicity can improve prognosis of the patients through tumor screening with better understanding of BAP1-TPDS.

METHODS

We edited five rare BAP1 variants with differing functional characteristics identified from patients with UM in HAP1 cells using CRISPR-Cas9 and assayed their effect on cell adhesion/spreading (at 4 h) and proliferation (at 48 h), measured as cell index (CI), using xCELLigence real-time analysis system.

RESULTS

In BAP1 knockout HAP1 cultures, cell number was half of wild type (WT) cultures at 48 h (p = 0.00021), reaching confluence later, and CI was 78% reduced (p < 0.0001). BAP1-TPDS-associated null variants c.67+1G>T and c.1780_1781insT, and a likely pathogenic missense variant c.281A>G reduced adhesion (all p ≤ 0.015) and proliferation by 74%-83% (all p ≤ 0.032). Another likely pathogenic missense variant c.680G>A reduced both by at least 50% (all p ≤ 0.032), whereas cells edited with likely benign one c.1526C>T grew similarly to WT.

CONCLUSIONS

BAP1 is essential for optimal fitness of HAP1 cells. Pathogenic and likely pathogenic BAP1 variants reduced cell fitness, reflected in adhesion/spreading and proliferation properties. Further, moderate effects were quantifiable. Variant modelling in HAP1 with CRISPR-Cas9 enabled functional analysis of coding and non-coding region variants in an endogenous expression system.

Modulation of the ubiquitin-proteasome system by phytochemicals: Therapeutic implications in malignancies with an emphasis on brain tumors

Regarding the multimechanistic nature of cancers, current chemo- or radiotherapies often fail to eradicate disease pathology, and frequent relapses or resistance to therapies occur. Brain malignancies, particularly glioblastomas, are difficult-to-treat cancers due to their highly malignant and multidimensional biology. Unfortunately, patients suffering from malignant tumors often experience poor prognoses and short survival periods. Thus far, significant efforts have been conducted to discover novel and more effective modalities. To that end, modulation of the ubiquitin-proteasome system (UPS) has attracted tremendous interest since it affects the homeostasis of proteins critically engaged in various cell functions, for example, cell metabolism, survival, proliferation, and differentiation. With their safe and multimodal actions, phytochemicals are among the promising therapeutic tools capable of turning the operation of various UPS elements. The present review, along with an updated outline of the role of UPS dysregulation in multiple cancers, provided a detailed discussion on the impact of phytochemicals on the UPS function in malignancies, especially brain tumors.