Pygo2 siRNA Inhibit the Growth and Increase Apoptosis of U251 Cell by Suppressing Histone H3K4 Trimethylation

Pygo2 as a novel biomarker in gastric cancer for monitoring drug resistance by upregulating MDR1

Chemotherapy is the main therapy for gastric cancer (GC) both before and after surgery, but the emergence of multidrug resistance (MDR) often leads to disease progression and recurrence. P-glycoprotein, encoded by MDR1, is a well-known multidrug efflux transporter involved in drug resistance development. Pygo2 overexpression has been identified in several cancers. Previous studies have shown that abnormal expression of Pygo2 is related to tumorigenesis, chemoresistance, and tumor progression. In this study, to evaluate the underlying relationship between Pygo2 and MDR1 in GC, we constructed GC drug-resistant cell lines, SGC7901/cis-platinum (DDP), and collected tissue from GC patients' pre-and post-chemotherapy. We found that Pygo2 was overexpressed in GC, especially in GC drug-resistant cell lines and GC patients who underwent neoadjuvant DDP-based chemotherapy. Pygo2 overexpression may precede MDR1 and correlates with MDR1 in GC patients. Furthermore, knock-down of Pygo2 induced downregulation of MDR1 and restored SGC7901/DDP's sensitivity to DDP. Further mechanistic analysis demonstrated that Pygo2 could modulate MDR1 transcription by binding to the MDR1 promoter region and promoting MDR1 activation. The overall findings reveal that Pygo2 may be a promising biomarker for monitoring drug resistance in GC by regulating MDR1.

Structure and function of Pygo in organ development dependent and independent Wnt signalling

Pygo is a nuclear protein containing two conserved domains, NHD and PHD, which play important roles in embryonic development and carcinogenesis. Pygo was first identified as a core component of the Wnt/β-catenin signalling pathway. However, it has also been reported that the function of Pygo is not always Wnt/β-catenin signalling dependent. In this review, we summarise the functions of both domains of Pygo and show that their functions are synergetic. The PHD domain mainly combines with transcription co-factors, including histone 3 and Bcl9/9l. The NHD domain mainly recruits histone methyltransferase/acetyltransferase (HMT/HAT) to modify lysine 4 of the histone 3 tail (H3K4) and interacts with Chip/LIM-domain DNA-binding proteins (ChiLS) to form enhanceosomes to regulate transcriptional activity. Furthermore, we summarised chromatin modification differences of Pygo in Drosophila (dPygo) and vertebrates, and found that Pygo displayes a chromatin silencing function in Drosophila, while in vertebates, Pygo has a chromatin-activating function due to the two substitution of two amino acid residues. Next, we confirmed the relationship between Pygo and Bcl9/9l and found that Pygo-Bcl/9l are specifically partnered both in the nucleus and in the cytoplasm. Finally, we discuss whether transcriptional activity of Pygo is Wnt/β-catenin dependent during embryonic development. Available information indications that the transcriptional activity of Pygo in embryonic development is either Wnt/β-catenin dependent or independent in both tissue-specific and cell-specific-modes.

Pygopus2 inhibits the efficacy of paclitaxel-induced apoptosis and induces multidrug resistance in human glioma cells

Anti-microtubule drugs, such as paclitaxel (PTX), are extensively used for the treatment of numerous cancers. However, growing evidence has shown that PTX resistance, either intrinsic or acquired, frequently occurs in patients and results in the failure of treatment, contributing to the high cancer mortality rate. Therefore, it is necessary to identify the genes or pathways involved in anti-microtubule drug resistance for future successful treatment of cancers. Pygopus2 (Pygo2), which contains a Zn-coordinated plant homeodomain (PHD) finger domain, is critical for β-catenin-dependent transcriptional switches in normal and malignant tissues and is over-expressed in various cancers, including human brain glioma. In this study, we report that over-expression of Pygo2 inhibited the efficacy of PTX and contributed to cell multidrug resistance in two different ways. First, over-expression of Pygo2 inhibited the PTX-induced phosphorylation of B-cell lymphoma 2 (Bcl-2), suppressing the proteolytic cleavage of procaspase-8/9 and further inhibiting the activation of caspase-3, which also inhibits the activation of the JNK/SAPK pathway, ultimately inhibiting cell apoptosis. Second, over-expression of Pygo2 facilitated the expression of P-glycoprotein, which acts as a drug efflux pump, by promoting the transcription of Multi-drug resistance 1 (MDR1) at the MDR1 promoter loci, resulting in acceleration of the efflux of PTX.

Ibuprofen reduces cell proliferation through inhibiting Wnt/β catenin signaling pathway in gastric cancer stem cells

Nowadays, most studies focused on cancer stem cells (CSCs) through their abilities to cause tumorigenicity, drug resistance, and cancer recurrence. On the other side, nonsteroidal anti-inflammatory drugs (NSAIDs) have been taken into consideration because of cheapness and availability. For the reasons mentioned above, we have studied the effect of ibuprofen as an NSAID on CSCs derived from AGS and MKN-45 gastric cancer cell lines to perform effective cancer therapy. We evaluated cell viability, spheroid body formation, monolayer, and soft agar colony formation to express the anti-cancer effect of ibuprofen on CSCs. Also, real-time RT-PCR data of stemness markers and genes affected on, or downstream of Wnt signaling pathway were evaluated. Our findings suggest that ibuprofen at 1,000 μM for 48 h can reduce cell proliferation, stemness features in CSCs by changing the expression level of CD44, OCT3/4, SOX2, Nanog, and KLF4 as stemness markers. Furthermore, ibuprofen can have an inhibitory role in Wnt signaling pathway by changing the expression level of some genes, including CTNNB1, CTNNBIP1, SMARCD1, PYGO2, SUFU, CASK, and KREMEN1. According to our study, ibuprofen has an anti-proliferative effect on CSCs derived from AGS and MKN-45 cells.

Role of Pygo2 in tumors

Pygo2, a vital component of the Wnt signaling pathway that was recently discovered, has been reported to be closely related to the tumorigenesis of several types of malignant tumors. There are two highly conservative domains named NHD in the N terminus and PHD in the C terminus of Pygo2. Previous studies have shown that the Pygo2 PHD domain can act as a protein code reader to link the chromatin remodeling complex to specific changes in gene transcription, as demonstrated for the Wnt target genes. Furthermore, the activity of the chromatin remodeling is further facilitated by the recruiting of histone methyltransferase and acetyltransferase through the interaction with the Pygo2 NHD domain. However, the molecular mechanism of Pygo2 in the tumor development is still poorly understood. In the present study, we intend to review the structure and role of Pygo2 in tumor progression.