Speckle-type POZ protein functions as a tumor suppressor in non-small cell lung cancer due to DNA methylation

SPOP downregulation promotes bladder cancer progression based on cancer cell-macrophage crosstalk via STAT3/CCL2/IL-6 axis and is regulated by VEZF1

Background: Cancer cells are intimately intertwined with tumor microenvironment (TME), fostering a symbiotic relationship propelling cancer progression. However, the interaction between cancer cells and tumor-associated macrophages (TAMs) in urothelial bladder cancer (UBC) remains poorly understood. Methods: UBC cell lines (5637, T24 and SW780), along with a monocytic cell line (U937) capable of differentiating into macrophage, were used in a co-culture system for cell proliferation and stemness by MTT, sphere formation assays. VEZF1/SPOP/STAT3/CCL2/ IL-6 axis was determined by luciferase reporter, ChIP, RNA-seq, co-IP, in vitro ubiquitination, RT-qPCR array and ELISA analyses. Results: We observed the frequent downregulation of SPOP, an E3 ubiquitin ligase, was positively associated with tumor progression and TAM infiltration in UBC patients and T24 xenografts. Cancer cell-TAM crosstalk promoting tumor aggressiveness was demonstrated dependent on SPOP deficiency: 1) In UBC cells, STAT3 was identified as a novel substrate of SPOP, and SPOP deficiency increased STAT3 protein stability, elevated chemokine CCL2 secretion, which induced chemotaxis and M2 polarization of macrophage; 2) In co-cultured macrophages, IL-6 secretion enhanced UBC cell proliferation and stemness. Additionally, transcription factor VEZF1 could directly activate SPOP transcription, and its overexpression suppressed the above effects in UBC cells. Conclusions: A pivotal role of SPOP in maintaining UBC stemness and remodeling immunosuppressive TME was revealed. Both the intrinsic signaling (dysregulated VEZF1/SPOP/STAT3 axis) and the extrinsic cues from TME (CCL2-IL-6 axis based on macrophages) promoted UBC progression. Targeting this crosstalk may offer a promising therapeutic strategy for UBC patients with SPOP deficiency.

Overexpression of SERPINA3 suppresses tumor progression by modulating SPOP/NF‑κB in lung cancer

The pathogenesis mechanism of lung cancer is very complex, with high incidence and mortality. Serpin family A member 3 (SERPINA3) expression levels were reduced in the sera of patients with lung cancer and may be a candidate diagnostic and prognostic survival biomarker in lung cancer, as previously reported. However, the detailed biological functions of SERPINA3 in the pathogenesis of lung cancer remain unknown. In the present study, it was aimed to explore the effects of SERPINA3 on the occurrence of lung cancer. SERPINA3 expression was assessed using bioinformatics database analysis and experimental detection. Then, the biological effects of SERPINA3 were investigated in a cell culture system and a xenograft model of human lung cancer. The potential regulatory mechanism of SERPINA3 in lung cancer was explored by data‑independent acquisition mass spectrometry (DIA‑MS) detection and further validated by western blotting (WB). The results indicated that SERPINA3 expression levels were significantly downregulated in lung cancer tissues and cell lines. At the cellular level, it was revealed that overexpressed SERPINA3 inhibited cell growth, proliferation, migration and invasion and promoted the apoptosis of lung cancer cells. Moreover, overexpressed SERPINA3 enhanced the sensitivity of lung cancer cells to osimertinib. In vivo, a xenograft model of human lung cancer was established with BALB/c nude mice. After the injection of A549 cells, the tumor growth of the tumor‑bearing mice in the SERPINA3‑overexpressing group increased more slowly, and the tumor volume was smaller than that in the empty‑vector group. Mechanistically, a total of 65 differentially expressed proteins were identified. It was found that the speckle‑type POZ protein (SPOP) was significantly upregulated in SERPINA3‑overexpressing H157 cells using DIA‑MS detection and analysis. WB validation showed that SPOP expression increased, and NF‑kappaB (NF‑κB) p65 was inhibited in cell lines and tumor tissues of mice when SERPINA3 was overexpressed. The present findings suggest that SERPINA3 is involved in the development of lung cancer and has an antineoplastic role in lung cancer.

SPOP in Cancer: Phenomena, Mechanisms and Its Role in Therapeutic Implications

Speckle-type POZ (pox virus and zinc finger protein) protein (SPOP) is a cullin 3-based E3 ubiquitin ligase adaptor protein that plays a crucial role in ubiquitin-mediated protein degradation. Recently, SPOP has attracted major research attention as it is frequently mutated in a range of cancers, highlighting pleiotropic tumorigenic effects and associations with treatment resistance. Structurally, SPOP contains a functionally critical N-terminal meprin and TRAF homology (MATH) domain for many SPOP substrates. SPOP has two other domains, including the internal Bric-a-brac-Tramtrack/Broad (BTB) domain, which is linked with SPOP dimerization and binding to cullin3, and a C-terminal nuclear localization sequence (NLS). The dysregulation of SPOP-mediated proteolysis is associated with the development and progression of different cancers since abnormalities in SPOP function dysregulate cellular signaling pathways by targeting oncoproteins or tumor suppressors in a tumor-specific manner. SPOP is also involved in genome stability through its role in the DNA damage response and DNA replication. More recently, studies have shown that the expression of SPOP can be modulated in various ways. In this review, we summarize the current understanding of SPOP's functions in cancer and discuss how to design a rational therapeutic target.

Novel insights into the SPOP E3 ubiquitin ligase: From the regulation of molecular mechanisms to tumorigenesis

Ubiquitin-mediated protein degradation is the primary biological process by which protein abundance is regulated and protein homeostasis is maintained in eukaryotic cells. Speckle-type pox virus and zinc finger (POZ) protein (SPOP) is a typical substrate adaptor of the Cullin 3-RING ligase (CRL3) family; it serves as a bridge between the Cullin 3 (Cul3) scaffold protein and its substrates. In recent years, SPOP has received increasing attention because of its versatility in its regulatory pathways and the diversity of tumor types involved. Mechanistically, SPOP substrates are involved in a wide range of biological processes, and abnormalities in SPOP function perturb downstream biological processes and promote tumorigenesis. Additionally, liquid-liquid phase separation (LLPS), a potential mechanism of membraneless organelle formation, was recently found to mediate the self-triggered colocalization of substrates with higher-order oligomers of SPOP. Herein, we summarize the structure of SPOP and the specific mechanisms by which it mediates the efficient ubiquitination of substrates. Additionally, we review the biological functions of SPOP, the regulation of SPOP expression, the role of SPOP in tumorigenesis and its therapeutic value.

Clinicopathological and prognostic significance of speckle-type POZ protein in cancers: a systematic review and meta-analysis

BACKGROUND

Controversial findings have been reported in the impact of speckle-type POZ protein (SPOP) on clinicopathological features and prognosis in diverse cancers. We conducted this meta-analysis to confirm whether SPOP was an effective biomarker to predict clinical stage, cancer differentiation and survival.

METHODS

We searched studies published before June 2021 through Medline, Embase, the Cochrane library register of controlled trials and Wanfang databases. The corrections of SPOP expression with expression disparity, tumor differentiation, clinical stage and survival were analyzed.

RESULTS

Our meta-analysis found that higher expression of SPOP was significantly associated with earlier clinical stage, well differentiation and better overall survival. Subgroup analysis showed that the SPOP expression of adjacent tissue was significantly higher than that in cancer tissues of prostate and liver. However, renal cancer presented improved expression of SPOP in cancer tissue.

CONCLUSIONS

SPOP has the potential function to act as a novel and effective biomarker for cancer diagnosis and prognostic stratification.

[Speckle-type POZ protein up-regulates c-Jun protein expression and promotes proliferation and invasion of renal carcinoma cells]

OBJECTIVE

To investigate the effect of speckle-type POZ protein (SPOP) on proliferation, apoptosis, migration and invasion of renal cell carcinoma (RCC) and explore the potential mechanisms.

OBJECTIVE

Renal carcinoma cell lines (786-O, A704, and Caki-2) cultured in vitro were transfected with a SPOP-overexpressing plasmid, and the changes in proliferation of the cells were detected using colony formation and MTT assay; TUNEL assay was used to assess apoptosis of the cells. The changes in migration and invasion abilities of the cells were examined using wound healing assay and Transwell assay. The mRNA and protein levels of SPOP and c-Jun in the transfected cells were measured using real-time PCR and Western blotting.

OBJECTIVE

SPOP over-expression obviously promoted the proliferation, migration and invasion of 786-O, A704 and Caki-2 cells (P < 0.05). Compared with the control cells, 786-o and Caki-2 cells over-expressing SPOP exhibited significantly lowered apoptosis rates (P < 0.05). The results of real-time PCR demonstrated that the transfected cells did not show obvious changes in the mRNA level of c-Jun, but the protein expressions of SPOP and c-jun increased significantly as shown by Western blotting (P < 0.05).

OBJECTIVE

SPOP can promote proliferation, migration, and invasion and suppress apoptosis of renal carcinoma cells possibly by promoting the expression of c-Jun.

SPOP and cancer: a systematic review

The initiation and progression of cancer is dependent on the acquisition of mutations in oncogenes or tumor suppressor genes that ultimately leads to the dysregulation of key regulatory pathways. Though these mutations often occur in direct regulators of such pathways, some may confer tumorigenic potential by indirectly targeting several pathways congruently thereby exerting pleiotropic effects. In recent years, the tumor suppressor gene Speckle Type POZ Protein (SPOP) has gained a lot of attention as it has been found to be altered in a variety of different cancers. SPOP appears to exert pleiotropic tumorigenic effects as multiple different regulatory pathways become dysregulated upon SPOP alterations. SPOP has been identified as an E3 ubiquitin ligase substrate binding subunit of the proteasome complex. Since protein degradation is critical in regulating proper cellular function it is not surprising that the proteasome pathway is often found to be disrupted in cancer. Many studies have now indicated that mutations or changes in the expression of SPOP are one of several underlying reasons of proteasome pathway disruption in different cancers. Ultimately, either SPOP downregulation or mutation promotes stabilization of direct SPOP targets which subsequently promotes cancer through the dysregulation of key regulatory pathways. In this review, we will discuss the current literature on cancer-specific SPOP alterations as well the SPOP targets that are stabilized, and the pathways that are dysregulated, as a result.

The association of speckle-type POZ protein with lymph node metastasis and prognosis in cancer patients: A meta-analysis

BACKGROUND

Speckle-type POZ protein (SPOP) has recently been reported as a prognostic tumor biomarker. However, the predictive value of SPOP remains controversial in human cancers. The current meta-analysis was performed to obtain a comprehensive evaluation of the relationship between SPOP expression and prognosis of cancer patients.

METHODS

Embase, Pubmed, Web of Science, and Chinese Biomedical Literature database were systematically searched up to January 2, 2019. The pooled hazard ratios (HRs) and/or pooled odds ratios (ORs) with 95% confidence intervals (CIs) were used to quantitatively assess the relationship of SPOP expression with prognosis and lymph node metastasis (LNM).

RESULTS

A total of 9 studies with 928 patients were included in this meta-analysis. The results showed that low SPOP expression was significantly related to poor overall survival (high/low: HR = 0.55; 95% CI: 0.38-0.79, P = .001), especially for digestive system cancers (high/low: HR = 0.46; 95% CI: 0.27-0.78, P = .003). However, SPOP expression did not affect progression-free survival in cancer patients (high/low: HR = 2.07; 95% CI: 0.16-26.70, P = .578). Additionally, the association between SPOP overexpression and LNM was positive in patients with clear cell renal cell carcinoma (ccRCC) (OR = 5.26; 95% CI: 1.66-16.68, P = .005) but negative in cancer patients without ccRCC (OR = 0.36; 95% CI: 0.21-0.62, P < .001).

CONCLUSION

Decreased SPOP expression could predict poor prognosis of cancer patients, suggesting that SPOP protein may be a useful prognostic biomarker in cancer patients.

Decreased expression of SLC16A12 mRNA predicts poor prognosis of patients with clear cell renal cell carcinoma

Solute carrier family 16, member 12 (SLC16A12) is a highly -expressed protein in the kidney and has been reported to participate in the transport of creatine. However, the clinical values of SLC16A12 in clear cell renal cell carcinoma (ccRCC) have not been explored.SLC16A12 RNA-seq data and clinical information were downloaded from the Cancer Genome Atlas (TCGA) database. We compared its expression in ccRCC and paracancerous tissues, then the result was further validated with our cohort. The impact on the clinical significance of SLC16A12 in ccRCC was also assessed.Compared with paracancerous tissue, SLC16A12 was significantly downregulated in the tumor tissues both in mRNA and protein level. In TCGA cohort, SLC16A12 mRNA expression was associated with several clinicopathological parameters, including T stages (P < .001), M stages (P = .009), TNM stages (P < .001), and differentiated grades (P = .001). Kaplan-Meier analysis showed that the overall survival of patients with low expression of SLC16A12 mRNA was significantly worse than that of patients with high expression (P < .001). Furthermore, both univariate (HR = 0.371, 95%CI: 0.269-0.513, P < .001) and multivariate (HR = 0.485, 95%CI: 0.297-0.793, P = .004) Cox regression analyses suggested that low expression of SLC16A12 mRNA was an independent prognostic factor for patients with ccRCC.Overall, we uncovered that decreased expression of SLC16A12 is a poor prognostic factor for patients with ccRCC. SLC16A12 might be a potential biomarker and therapeutic target in ccRCC.

Hypermethylation of the G protein-coupled receptor kinase 6 (GRK6) promoter inhibits binding of C/EBPα, and GRK6 knockdown promotes cell migration and invasion in lung adenocarcinoma cells

We previously reported that the expression of G protein-coupled receptor kinase 6 (GRK6) is significantly downregulated in lung adenocarcinoma (LADC) tissues, and low expression levels of GRK6 are correlated with poor survival prognosis. However, the specific regulatory mechanisms and functions of GRK6 in LADC remain unknown. Here, we report that GRK6 mRNA expression levels are downregulated in LADC tissues compared to those in matched adjacent non-tumor tissues (P < 0.001). The promoter of the GRK6 gene was found to be hypermethylated in LADC tissues, and its methylation was correlated with both GRK6 expression and pathology grade. GRK6 promoter hypermethylation may predict shorter overall survival. Treatment with 5-aza-2'-deoxycytidine significantly enhanced GRK6 gene expression. Four binding sites of CCAAT/enhancer-binding protein-α (C/EBPα) in the CpG island of the GRK6 gene promoter were predicted in silico, of which three sites were further confirmed by ChIP. Decreased binding of C/EBPα to binding sites 1, 3 and 4 of the GRK6 gene promoter was observed in LADC tissues. Inhibition of C/EBPα significantly inhibited GRK6 expression, while overexpression of C/EBPα significantly promoted GRK6 expression. In addition, overexpression of GRK6 significantly suppressed, while GRK6 knockdown promoted cell migration and invasion. Overexpression of GRK6 enhanced E-cadherin expression and suppressed vimentin expression, and silencing of GRK6 had the opposite effects. Furthermore, ectopic expression of GRK6 significantly decreased matrix metalloproteinase (MMP) 2 and MMP7 protein expression levels. Our findings suggest that hypermethylation of the GRK6 gene promoter suppressed binding of C/EBPα, thereby contributing to the promotion of cell migration and invasion. The methylation status of the GRK6 promoter might be suitable for use as an epigenetic biomarker, and the C/EBPα-GRK6 signaling pathway may be a potential target for LADC.