Pivotal role of augmented αB-crystallin in tumor development induced by deficient TSC1/2 complex

Fluorouracil exacerbates alpha-crystallin B chain-mediated cell migration in triple-negative breast cancer cell lines

Among triple-negative breast cancer (TNBC) subtypes, the basal-like 2 (BL2) subtype shows the lowest survival rate and the highest risk of metastasis after treatment with chemotherapy. Research has shown that αB-crystallin (CRYAB) is more highly expressed in the basal-like subtypes than in the other subtypes and is associated with brain metastasis in TNBC patients. We therefore hypothesized that αB-crystallin is associated with increased cell motility in the BL2 subtype after treatment with chemotherapy. Here, we evaluated the effect of fluorouracil (5-FU), a typical chemotherapy for the treatment of TNBC, on cell motility by utilizing a cell line with high αB-crystallin expression (HCC1806). A wound healing assay revealed that 5-FU significantly increased cell motility in HCC1806 cells, but not in MDA-MB-231 cells, which have low αB-crystallin expression. Also, cell motility was not increased by 5-FU treatment in HCC1806 cells harboring stealth siRNA targeting CRYAB. In addition, the cell motility of MDA-MB-231 cells overexpressing αB-crystallin was significantly higher than that of MDA-MB-231 cells harboring a control vector. Thus, 5-FU increased cell motility in cell lines with high, but not low, αB-crystallin expression. These results suggest that 5-FU-induced cell migration is mediated by αB-crystallin in the BL2 subtype of TNBC.

αB-crystallin/HSPB2 is critical for hyperactive mTOR-induced cardiomyopathy

Even though aberrant mechanistic target of rapamycin (mTOR) signaling is known to cause cardiomyopathy, its underlying mechanism remains poorly understood. Because augmentation of αB-crystallin and hspB2 was presented in the cortical tubers and lymphangioleiomyomatosis of tuberous sclerosis complex patients, we deciphered the role of αB-crystallin and its adjacent duplicate gene, hspB2, in hyperactive mTOR-induced cardiomyopathy. Cardiac Tsc1 deletion (T1-hKO) caused mouse mTOR activation and cardiomyopathy. Overexpression of αB-crystallin and hspB2 was presented in the hearts of these mice. Knockout of αB-crystallin/hspB2 reversed deficient Tsc1-mediated fetal gene expression, mTOR activation, mitochondrial damage, cardiomyocyte vacuolar degeneration, cardiomyocyte size, and fibrosis of T1-hKO mice. These cardiac-Tsc1; αB-crystallin; hspB2 triple knockout (tKO) mice had improved cardiac function, smaller heart weight to body weight ratio, and reduced lethality compared with T1-hKO mice. Even though activated mTOR suppressed autophagy in T1-hKO mice, ablation of αB-crystallin and hspB2 failed to restore autophagy in tKO mice. mTOR inhibitors suppressed αB-crystallin expression in T1-hKO mice and rat cardiomyocyte line H9C2. Starvation of H9C2 cells activated autophagy and suppressed αB-crystallin expression. Since inhibition of autophagy restored αB-crystallin expression in starved H9C2 cells, autophagy is a negative regulator of αB-crystallin expression. mTOR thus stimulates αB-crystallin expression through suppression of autophagy. In conclusion, αB-crystallin and hspB2 play a pivotal role in Tsc1 knockout-related cardiomyopathy and are therapeutic targets of hyperactive mTOR-associated cardiomyopathy.

Prognostic value of biomarkers EpCAM and αB-crystallin associated with lymphatic metastasis in breast cancer by iTRAQ analysis

Background

Metastasis is responsible for the majority of deaths in a variety of cancer types, including breast cancer. Although several factors or biomarkers have been identified to predict the outcome of patients with breast cancer, few studies have been conducted to identify metastasis-associated biomarkers.

Methods

Quantitative iTRAQ proteomics analysis was used to detect differentially expressed proteins between lymph node metastases and their paired primary tumor tissues from 23 patients with metastatic breast cancer. Immunohistochemistry was performed to validate the expression of two upregulated (EpCAM, FADD) and two downregulated (NDRG1, αB-crystallin) proteins in 190 paraffin-embedded tissue samples. These four proteins were further analyzed for their correlation with clinicopathological features in 190 breast cancer patients.

Results

We identified 637 differentially regulated proteins (397 upregulated and 240 downregulated) in lymph node metastases compared with their paired primary tumor tissues. Data are available via ProteomeXchange with identifier PXD013931. Furthermore, bioinformatics analysis using GEO profiling confirmed the difference in the expression of EpCAM between metastases and primary tumors tissues. Two upregulated (EpCAM, FADD) and two downregulated (NDRG1, αB-crystallin) proteins were associated with the progression of breast cancer. Obviously, EpCAM plays a role in the metastasis of breast cancer cells to the lymph node. We further identified αB-crystallin as an independent biomarker to predict lymph node metastasis and the outcome of breast cancer patients.

Conclusion

We have identified that EpCAM plays a role in the metastasis of breast cancer cells to the lymph node. αB-crystallin, a stress-related protein that has recently been shown to be important for cell invasion and survival, was identified as a potential prognostic biomarker to predict the outcome of breast cancer patients.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-6016-3) contains supplementary material, which is available to authorized users.

Deficient TSC1/TSC2-complex suppression of SOX9-osteopontin-AKT signalling cascade constrains tumour growth in tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is an autosomal dominant genetic disorder featured with multi-organ benign tumours. Disruption of TSC1/TSC2 complex suppression on mammalian/mechanistic target of rapamycin (mTOR) signalling causes TSC. Hyperactive mTOR-mediated negative feedback regulation of AKT partially contributes to the benign nature of TSC-associated tumours. In this study, we demonstrated that osteopontin (OPN) was dramatically reduced by loss of TSC1/TSC2 complex in Tsc2-null mouse embryonic fibroblasts (MEFs), rat uterine leiomyoma-derived Tsc2-deficient cells, genetically modified mouse TSC models, and clinical samples. TSC1/TSC2 complex upregulation of OPN expression is mediated by transcription factor SOX9 in an mTOR-independent manner. Moreover, ablation of OPN by deficient TSC1/TSC2 complex contributed to inactivation of AKT in TSC cells. Lastly, the abundance of OPN dictated the potency of cell proliferation and tumour development. Therefore, loss of TSC1/TSC2 complex led to mTOR-independent inhibition of AKT at least partially through downregulation of the SOX9-OPN signalling cascade. We suggest that the decreased SOX9-OPN-AKT signalling pathway safeguard against the development of malignant tumours in TSC patients.

Huaier aqueous extract inhibits proliferation and metastasis of tuberous sclerosis complex cell models through downregulation of JAK2/STAT3 and MAPK signaling pathways

Tuberous sclerosis complex (TSC) is a genetic disorder with formation of benign tumors in many different organs. It has attracted increasing attention from researchers to search for therapeutic drugs for TSC patients. Traditional Chinese medicine (TCM) has become an important source for finding antitumor drugs. Trametes robiniophila Μurr. (Huaier) is a kind of officinal fungi in China and has been applied in TCM for approximately 1,600 years. A large number of clinical applications have revealed that Huaier has good antitumor effect. In this study, we have investigated the effects of Huaier aqueous extract on two TSC cell models, including inhibition of proliferation, induction of apoptosis, cell cycle arrest, and anti-metastasis. We demonstrated that Huaier aqueous extract inhibited JAK2/STAT3 and MAPK signaling pathways in a dose-dependent manner. Therefore, based on the low toxicity and the multi-targets of Huaier treatment, Huaier may be a promising therapeutic drug for TSC.

αB-crystallin: Portrait of a malignant chaperone as a cancer therapeutic target

αB-crystallin is a widely expressed member of the small heat shock protein family that protects cells from stress by its dual function as a molecular chaperone to preserve proteostasis and as a cell death antagonist that negatively regulates components of the conserved apoptotic cell death machinery. Deregulated expression of αB-crystallin occurs in a broad array of solid tumors and has been linked to tumor progression and poor clinical outcomes. This review will focus on new insights into the molecular mechanisms by which oncogenes, oxidative stress, matrix detachment and other tumor microenvironmental stressors deregulate αB-crystallin expression. We will also review accumulating evidence pointing to an essential role for αB-crystallin in the multi-step metastatic cascade whereby tumor cells colonize distant organs by circumventing a multitude of barriers to cell migration and survival. Finally, we will evaluate emerging strategies to therapeutically target αB-crystallin and/or interacting proteins to selectively activate apoptosis and/or derail the metastatic cascade in an effort to improve outcomes for patients with metastatic disease.

NFκB up-regulation of glucose transporter 3 is essential for hyperactive mammalian target of rapamycin-induced aerobic glycolysis and tumor growth

Accumulating evidence indicates that mammalian target of rapamycin (mTOR) exerts a crucial role in aerobic glycolysis and tumorigenesis, but the underlying mechanisms remain largely obscure. Results from Tsc1- or Tsc2-null mouse embryonic fibroblasts (MEFs) and human cancer cell lines consistently indicate that the expression of glucose transporter 3 (Glut3) is dramatically up-regulated by mTOR. The rapamycin-sensitive mTOR complex 1 (mTORC1), but not the rapamycin-insensitive mTOR complex 2 (mTORC2), was involved in the regulation of Glut3 expression. Moreover, mTORC1 enhances Glut3 expression through the activation of the IKK/NFκB pathway. Depletion of Glut3 led to the suppression of aerobic glycolysis, the inhibition of cell proliferation and colony formation, and the attenuation of the tumorigenic potential of the cells with aberrantly hyper-activated mTORC1 signaling in nude mice. We conclude that Glut3 is a downstream target of mTORC1, and it is critical for oncogenic mTORC1-mediated aerobic glycolysis and tumorigenesis. Hence Glut3 may be a potential target for therapy against cancers caused by the aberrantly activated mTORC1 signaling.