BET inhibition increases βIII-tubulin expression and sensitizes metastatic breast cancer in the brain to vinorelbine

Abstract

Metastases from primary breast cancer result in poor survival. βIII-tubulin (TUBB3) has been established as a therapeutic target for breast cancer metastases specifically to the brain. In this study, we conducted a systematic analysis to determine the regulation of TUBB3 expression in breast cancer metastases to the brain and strategically target these metastases using vinorelbine (VRB), a drug approved by the U.S. Food and Drug Administration (FDA). We found that human epidermal growth factor receptor 2 (HER2) signaling regulates TUBB3 expression in both trastuzumab-sensitive and trastuzumab-resistant neoplastic cells. We further discovered that bromodomain and extra-terminal domain (BET) inhibition increases TUBB3 expression, rendering neoplastic cells more susceptible to apoptosis by VRB. Orthotopic xenograft assays using two different breast cancer cell models revealed a reduction in tumor volume with BET inhibition and VRB treatment. In addition, in vivo studies using a model of multiple brain metastasis (BM) showed improved survival with the combination of radiation + BET inhibitor (iBET-762) + VRB (75% long-term survivors, P < 0.05). Using in silico analysis and BET inhibition, we found that the transcription factor myeloid zinc finger-1 (MZF-1) protein binds to the TUBB3 promoter. BET inhibition decreases MZF-1 expression and subsequently increases TUBB3 expression. Overexpression of MZF-1 decreases TUBB3 expression and reduces BM in vivo, whereas its knockdown increases TUBB3 expression in breast cancer cells. In summary, this study demonstrates a regulatory mechanism of TUBB3 and provides support for an application of BET inhibition to sensitize breast cancer metastases to VRB-mediated therapy.

Identification of prognostic alternative splicing events related to the immune microenvironment of hepatocellular carcinoma

“…Some genes in our prognostic signature model have been clarified to be involved in the progression of various tumors, including FGL1 (fibrinogen-like protein 1), TUBB3 (tubulin beta 3), TNIP1 (TNF-α-induced protein 3-interacting protein 1), CALD1 (caldesmon 1), ARPP19 (cAMP-regulated phosphoproteins 19), FCGRT (Fc fragment of IgG receptor and transporter), ANKDD1A (ankyrin repeat and death domain containing 1A) and SMARCC2 (SWI/SNF related, matrix associated, actin dependent regulator of chromatin subfamily C member 2) (Wang et al 2019 ; Kanojia et al 2020 ; Yang et al 2019b ; Liu et al 2018 ; Ye et al 2020 ; Xue et al 2020 ; Feng et al 2018 ; Yuan et al 2018 ). Among these survival-related genes, FGL1 and ANKDD1A were intriguingly closely associated with the tumor microenvironment and immune infiltration.…”

Metabolic Stress Adaptations Underlie Mammary Gland Morphogenesis and Breast Cancer Progression

“…However, the incidence of brain metastases is 30-55% in patients with HER2 positive breast cancers. Brain-predominant genes critical for the establishment of HER2 positive breast cancer brain metastases include a cytoskeletal protein βIII-tubulin (encoded by TUBB3 gene) [85] and the fatty acid-binding protein 7 (encoded by FABP7 gene) [86]. FABP7, a brain-specific intracellular lipid-binding protein, regulates fatty acid uptake and intracellular lipid droplet formation.…”

βIII-Tubulin Gene Regulation in Health and Disease

“…Recent work has identified that MZF1 is able to bind to the TUBB3 loci, with three potential sites predicted up to 600 base pairs upstream of the first exon of TUBB3 transcript variant 2 ( Kanojia et al, 2020 ). The ability of MZF1 to bind to the TUBB3 loci was identified while looking for means to upregulate βIII-tubulin expression in HER2 positive breast cancer in an effort to induce sensitivity to the TBA, vinorelbine ( Kanojia et al, 2020 ).…”

“…Recent work has identified that MZF1 is able to bind to the TUBB3 loci, with three potential sites predicted up to 600 base pairs upstream of the first exon of TUBB3 transcript variant 2 ( Kanojia et al, 2020 ). The ability of MZF1 to bind to the TUBB3 loci was identified while looking for means to upregulate βIII-tubulin expression in HER2 positive breast cancer in an effort to induce sensitivity to the TBA, vinorelbine ( Kanojia et al, 2020 ). Building on previous work that identified TUBB3 expression to be modulated by the members of the Bromdodmain and Extraterminal (BET) protein family ( Piunti et al, 2017 ), Kanojia et al (2020) identified increased TUBB3 /βIII-tubulin expression in response to BET inhibition which led to increased sensitivity to Vinorelbine both in vitro and in vivo ( Kanojia et al, 2020 ).…”

“…The ability of MZF1 to bind to the TUBB3 loci was identified while looking for means to upregulate βIII-tubulin expression in HER2 positive breast cancer in an effort to induce sensitivity to the TBA, vinorelbine ( Kanojia et al, 2020 ). Building on previous work that identified TUBB3 expression to be modulated by the members of the Bromdodmain and Extraterminal (BET) protein family ( Piunti et al, 2017 ), Kanojia et al (2020) identified increased TUBB3 /βIII-tubulin expression in response to BET inhibition which led to increased sensitivity to Vinorelbine both in vitro and in vivo ( Kanojia et al, 2020 ). Seeking a mechanism to account for why BET inhibition was promoting TUBB3 expression, the TUBB3 promoter (GH6J089920) was scanned and led to the identification of several potential binding sites for transcription factors ( Kanojia et al, 2020 ).…”