AMD1 promotes breast cancer aggressiveness via a spermidine-eIF5A hypusination-TCF4 axis

BACKGROUND

Basal-like breast cancer (BLBC) is the most aggressive subtype of breast cancer due to its aggressive characteristics and lack of effective therapeutics. However, the mechanism underlying its aggressiveness remains largely unclear. S-adenosylmethionine decarboxylase proenzyme (AMD1) overexpression occurs specifically in BLBC. Here, we explored the potential molecular mechanisms and functions of AMD1 promoting the aggressiveness of BLBC.

METHODS

The potential effects of AMD1 on breast cancer cells were tested by western blotting, colony formation, cell proliferation assay, migration and invasion assay. The spermidine level was determined by high performance liquid chromatography. The methylation status of CpG sites within the AMD1 promoter was evaluated by bisulfite sequencing PCR. We elucidated the relationship between AMD1 and Sox10 by ChIP assays and quantitative real-time PCR. The effect of AMD1 expression on breast cancer cells was evaluated by in vitro and in vivo tumorigenesis model.

RESULTS

In this study, we showed that AMD1 expression was remarkably elevated in BLBC. AMD1 copy number amplification, hypomethylation of AMD1 promoter and transcription activity of Sox10 contributed to the overexpression of AMD1 in BLBC. AMD1 overexpression enhanced spermidine production, which enhanced eIF5A hypusination, activating translation of TCF4 with multiple conserved Pro-Pro motifs. Our studies showed that AMD1-mediated metabolic system of polyamine in BLBC cells promoted tumor cell proliferation and tumor growth. Clinically, elevated expression of AMD1 was correlated with high grade, metastasis and poor survival, indicating poor prognosis of breast cancer patients.

CONCLUSION

Our work reveals the critical association of AMD1-mediated spermidine-eIF5A hypusination-TCF4 axis with BLBC aggressiveness, indicating potential prognostic indicators and therapeutic targets for BLBC.

IMPA2 promotes basal-like breast cancer aggressiveness by a MYC-mediated positive feedback loop

Basal-like breast cancer (BLBC) is the most aggressive subtype with poor prognosis; however, the mechanisms underlying aggressiveness in BLBC remain poorly understood. In this study, we showed that in contrast to other subtypes, inositol monophosphatase 2 (IMPA2) was dramatically increased in BLBC. Mechanistically, IMPA2 expression was upregulated due to copy number amplification, hypomethylation of IMPA2 promoter and MYC-mediated transcriptional activation. IMPA2 promoted MI-PI cycle and IP3 production, and IP3 then elevated intracellular Ca2+ concentration, leading to efficient activation of NFAT1. In turn, NFAT1 up-regulated MYC expression, thereby fulfilling a positive feedback loop that enhanced aggressiveness of BLBC cells. Knockdown of IMPA2 expression caused the inhibition of tumorigenicity and metastasis of BLBC cells in vitro and in vivo. Clinically, high IMPA2 expression was strongly correlated with large tumor size, high grade, metastasis and poor survival, indicating poor prognosis in breast cancer patients. These findings suggest that IMPA2-mediated MI-PI cycle allows crosstalk between metabolic and oncogenic pathways to promote BLBC progression.

WNT signaling pathway regulator-FRAT2 affects oncogenesis and prognosis of basal-like breast cancer

Background

Breast cancer is the most common malignant cancer in women worldwide and is one of the leading causes of cancer death. Basal-like breast cancer (BLBC) is an aggressive subtype of breast cancer for which targeted therapy has poor efficacy. Therefore, research into the molecular pathogenesis of BLBC is urgent for developing effective targeted therapeutic treatments.

Methods

We collected relevant data from the Cancer Genome Atlas (TCGA), including transcriptome, copy number variation, and survival data. We also gathered 30 pairs clinical samples of cancer tissues and non-cancerous tissues to perform Western Blotting (WB) to reveal the encoded protein expression levels. Besides, we knocked down frequently rearranged in advanced T-cell lymphomas 2 (FRAT2) expression in two representative cell lines (T47D and MDA-MB-231 cells). The cell cycle progression was analyzed, while the apoptosis experiments were also conducted to explore the molecular pathogenesis of FRAT2 in BLBC.

Results

The aberrant activation of the WNT pathway and highly expressed FRAT2 were specifically identified across the BLBC genome comparing to other types of tumor. In addition, FRAT2 expression was found to be positively associated with its copy number variations (P=9.126×10^-23). For further investigation, we found the expression level of FRAT2 was related to the poor overall survival of BLBC patients (P=0.049). The results of WB revealed that FRTA2-encoded protein was overexpressed in BLBC tissues. Based on results in T47D and MDA-MB-231 cells in vitro, we found that knocking down FRAT2 can inhibit the proliferation of these two cell lines. In cell cycle progression experiments, cell cycle arrested in the G2/M phase. Meanwhile, increased apoptosis was also found in the shFRAT2 cell group in vitro.

Conclusions

In BLBC basal-like breast cancer, we can assume that FRAT2 is a potential treatment target.

Morphological and pathological features of basal-like breast cancer

Basal-like breast cancer (BLBC) is characterized by high grade, high mitotic indices, presence of central necrotic or fibrotic zones, and lymphocytic infiltrate. Patients presenting with BLBC have a poor prognosis and a short-term disease-free and overall survival. BLBCs may include different histological types of breast cancers but the most common histological type is represented by invasive ductal carcinomas of no special type (IDC-NST). Typical immunohistochemical markers for these tumors are basal-type cytokeratin markers such as CK5/6, CK14, CK17, but several BLBCs also express luminal-type CKs, such as CK8/18, CK19. Different molecular alterations, including BRCA1 dysfunction, p53 mutations, up-regulation of EGFR, inactivation of PTEN and the aberrant expression of many non-coding RNAs molecules are detected in BLBC cells suggesting the possibility of defining new targeted therapeutic strategies for this tumor type.