Signal transducer and activator of transcription 3 is a transcriptional factor regulating the gene expression of SALL4

Immunotherapy, targeted therapy, and their cross talks in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a challenging malignancy with limited treatment options beyond surgery and chemotherapy. Recent advancements in targeted therapies and immunotherapy, including PD-1 and PD-L1 monoclonal antibodies, have shown promise, but their efficacy has not met expectations. Biomarker testing and personalized medicine based on genetic mutations and other biomarkers represent the future direction for HCC treatment. To address these challenges and opportunities, this comprehensive review discusses the progress made in targeted therapies and immunotherapies for HCC, focusing on dissecting the rationales, opportunities, and challenges for combining these modalities. The liver's unique physiology and the presence of fibrosis in many HCC patients pose additional challenges to drug delivery and efficacy. Ongoing efforts in biomarker development and combination therapy design, especially in the context of immunotherapies, hold promise for improving outcomes in advanced HCC. Through exploring the advancements in biomarkers and targeted therapies, this review provides insights into the challenges and opportunities in the field and proposes strategies for rational combination therapy design.

Production and characterization of a new specific monoclonal antibody against A-isoform of SALL4: A novel emerging testicular cancer marker

SALL4 transcription factor plays an important role to maintain the pluripotent and self-renewal of embryonic stem cells. It contributes to the growth of many cancers and embryonic development. With the exception of spermatogonia, SALL4 expression is silenced in most adult tissues after birth; nevertheless, it is re-expressed in a subset of different solid malignancies. SALL4 is a new, precise biomarker for testicular germ cell cancers that was just introduced. The whole isoform of SALL4 is called SALL4-A. Regarding the lack of antibody against human SALL4 isoforms, the pattern of expression, the role of each isoform remain unknown. Furthermore, in isoform specific evaluations, we aimed, for the first time, to produce and characterize mAb against human SALL4-A. Immunization of mice were performed with a selected 33-mer synthetic peptide of SALL4-A conjugated with KLH. Hybridoma cells were screened by ELISA for positive reactivity with SALL4-A peptide. From the ascites fluid of mice that had been injected with hybridoma cells, anti-SALL4-A mAbs were isolated using a protein G column. Reactivity of the mAbs was evaluated using the peptide and SALL4-A recombinant protein by ELISA and IHC on testicular cancer tissue as positive control, and normal kidney, stomach and prostate tissues as negative control. The produced mAb could well detect SALL4-A in testicular cancer tissues using IHC, while the reactivity was negative in normal kidney, stomach and prostate tissues. Using ELISA, the mAb affinity for the peptide and SALL4-A recombinant protein was assessed, and it was shown to be reasonably high. The mAb detected SALL4-A in nucleus and cytoplasm of several cancer cells and spermatogonia in testicular cancer tissue. In addition, it could recognize SALL4-A recombinant protein. Our produced monoclonal antibody against isoform-A of human SALL4 can specifically recognize SALL4-A using either IHC or ELISA. We hope that this mAb could help researchers in isoform-specific study of human SALL4.

SALL4: An Intriguing Therapeutic Target in Cancer Treatment

Spalt-Like Transcription Factor 4 (SALL4) is a critical factor for self-renewal ability and pluripotency of stem cells. On the other hand, various reports show tight relation of SALL4 to cancer occurrence and metastasis. SALL4 exerts its effects not only by inducing gene expression but also repressing a large cluster of genes through interaction with various epigenetic modifiers. Due to high expression of SALL4 in cancer cells and its silence in almost all adult tissues, it is an ideal target for cancer therapy. However, targeting SALL4 meets various challenges. SALL4 is a transcription factor and designing appropriate drug to inhibit this intra-nucleus component is challenging. On the other hand, due to lack of our knowledge on structure of the protein and the suitable active sites, it becomes more difficult to reach the appropriate drugs against SALL4. In this review, we have focused on approaches applied yet to target this oncogene and discuss the potential of degrader systems as new therapeutics to target oncogenes.

Co-overexpression of self-renewal markers SALL4 and HIWI is correlated with depth of tumor invasion and metastasis in colorectal cancer

Background

SALL4 and HIWI are involved in the maintenance of self-renewal capacity of stem cells. Several scrutinizes have demonstrated that SALL4 and HIWI play a key role in cancer development. However, the correlation between these genes regarding different clinicopathological features of patients with colorectal cancer (CRC) is still unclear.

Methods

The expression of SALL4 and HIWI in different clinicopathological features of 46 CRC patients was analyzed using relative comparative real-time PCR.

Results

mRNA expression levels of SALL4 and HIWI genes were significantly correlated with each other in CRC (P = 0.013, Pearson correlation = 0.364). HIWI expression was notably increased in tumors with overexpression of SALL4 in comparison with other samples. This correlation was significant in non-metastatic CRCs compared to the metastatic tumors and in invaded tumors to the serosa (T3/T4) in comparison with non-invaded tumors (T1/T2).

Conclusions

Based on the significant association of SALL4 and HIWI in different indices of CRC poor prognosis, it may be concluded that simultaneous expression of these genes is notably contributed to the growth and development of the disease, and therefore, their co-overexpression may be considered for prognosis of aggressive CRCs.

SALL Proteins; Common and Antagonistic Roles in Cancer

Simple Summary

Transcription factors play essential roles in regulating gene expression, impacting the cell phenotype and function, and in the response of cells to environmental conditions. Alterations in transcription factors, including gene amplification or deletion, point mutations, and expression changes, are implicated in carcinogenesis, cancer progression, metastases, and resistance to cancer treatments. Not surprisingly, transcription factor activity is altered in numerous cancers, representing a unique class of cancer drug targets. This review updates and integrates information on the SALL family of transcription factors, highlighting the synergistic and/or antagonistic functions they perform in various cancer types.

Abstract

SALL proteins are a family of four conserved C2H2 zinc finger transcription factors that play critical roles in organogenesis during embryonic development. They regulate cell proliferation, survival, migration, and stemness; consequently, they are involved in various human genetic disorders and cancer. SALL4 is a well-recognized oncogene; however, SALL1–3 play dual roles depending on the cancer context and stage of the disease. Current reviews of SALLs have focused only on SALL2 or SALL4, lacking an integrated view of the SALL family members in cancer. Here, we update the recent advances of the SALL members in tumor development, cancer progression, and therapy, highlighting the synergistic and/or antagonistic functions they perform in similar cancer contexts. We identified common regulatory mechanisms, targets, and signaling pathways in breast, brain, liver, colon, blood, and HPV-related cancers. In addition, we discuss the potential of the SALL family members as cancer biomarkers and in the cancer cells’ response to therapies. Understanding SALL proteins’ function and relationship will open new cancer biology, clinical research, and therapy perspectives.

Up-Regulation of SALL4 Is Associated With Survival and Progression via Putative WNT Pathway in Gastric Cancer

SALL4, a transcriptional factor involved in embryonic stem cell self-renewal and pluripotency, is overexpressed in gastric cancer (GC). However, the association of SALL4 with the survival of GC patients is not well-understood, and the role of SALL4 in cancer progression is still unknown. In the present study, a total of 1,815 GC patients who underwent radical resection at Peking Cancer Hospital were included consecutively from 2015 to 2018, confirming the prognostic value of SALL4 and validating by data from TCGA and GEO. The protein and mRNA expression levels of SALL4 were evaluated by immunohistochemistry and qPCR, respectively. Besides, GSEA and WGCNA were applied to explore the SALL4-related cancer-promoting signaling pathways and gene modules. Our results showed that overexpression of SALL4 was observed in 16.7% of GC patients. SALL4 positivity was associated with male, older age, mixed-type histology, late stages, lymphatic metastasis, vascular invasion, non-cardia location, high AFP level, and no EBV infection background. SALL4 could be served as a marker for prognostic prediction in GC, and SALL4-positive GC was significantly associated with shortened survival. Further, the bioinformatic analysis indicated that the Wnt/β-catenin signaling pathway was activated in SALL4-high cases compared with SALL4-low cases. Expression of SALL4 was also positively correlated with the expression of multiple co-expressed genes, such as TRIB3, which plays an important role in activating the Wnt/β-catenin pathway. Our findings indicate that SALL4 is associated with clinicopathological features related to cancer progression in GC and its function in the Wnt/β-catenin pathway.

MLAA-34 knockdown shows enhanced antitumor activity via JAK2/STAT3 signaling pathway in acute monocytic leukemia

MLAA-34 is a novel leukemia-associated gene closely related to the carcinogenesis of acute monocytic leukemia (AML). MLAA-34 over expression has been observed to inhibit apoptosis in vitro. JAK2/STAT3 pathway plays an important role in cell proliferation, differentiation and inhibition of apoptosis in number of cancers. However, the relationship and interaction between MLAA-34 and JAK2/STAT3 has never been investigated in AML.

This study investigates and reports a novel relationship between MLAA-34 and JAK2/STAT3 pathway in AML both in vitro and in vivo. We constructed MLAA-34 knockdown vector and transfected U937 cells to observe its apoptotic activities in relation to JAK2/STAT3 signaling pathway in vitro and then in vivo in mouse model. Levels of expression of MLAA-34 and JAK2/STAT3 and its downstream targets were also measured in AML patients and a few volunteers.

We found that MLAA-34 knockdown increased U937 apoptosis in vitro and inhibited tumor growth in vivo. Components of the canonical JAK2/STAT3 pathway or its downstream targets, including c-myc, bcl-2, Bax, and caspase-3, were shown to be involved in the carcinogenesis of AML. We also found that the JAK2/STAT3 pathway positively regulated MLAA-34 expression. We additionally identified a STAT3 binding site in the MLAA-34 promoter where STAT3 binds directly and activates MLAA-34 expression. In addition, MLAA-34 was found to form a complex with JAK2 and was enhanced by JAK2 activation. Correlation of MLAA-34 and JAK2/STAT3 was further confirmed in AML patients.

In conclusion, MLAA-34 is a novel regulator for JAK2/STAT3 signaling, and in turn, is regulated by this interaction in a positive feedback loop. Thus we report a novel model of interaction mechanism between MLAA-34 and JAK2/STAT3 which can be utilized as a potential target for a novel therapeutic approach in AML.

Complex Tissue Regeneration in Mammals Is Associated With Reduced Inflammatory Cytokines and an Influx of T Cells

While mammals tend to repair injuries, other adult vertebrates like salamanders and fish regenerate damaged tissue. One prominent hypothesis offered to explain an inability to regenerate complex tissue in mammals is a bias during healing toward strong adaptive immunity and inflammatory responses. Here we directly test this hypothesis by characterizing part of the immune response during regeneration in spiny mice (Acomys cahirinus and Acomys percivali) vs. fibrotic repair in Mus musculus. By directly quantifying cytokines during tissue healing, we found that fibrotic repair was associated with a greater release of pro-inflammatory cytokines (i.e., IL-6, CCL2, and CXCL1) during acute inflammation in the wound microenvironment. However, reducing inflammation via COX-2 inhibition was not sufficient to reduce fibrosis or induce a regenerative response, suggesting that inflammatory strength does not control how an injury heals. Although regeneration was associated with lower concentrations of many inflammatory markers, we measured a comparatively larger influx of T cells into regenerating ear tissue and detected a local increase in the T cell associated cytokines IL-12 and IL-17 during the proliferative phase of regeneration. Taken together, our data demonstrate that a strong adaptive immune response is not antagonistic to regeneration and that other mechanisms likely explain the distribution of regenerative ability in vertebrates.

Complex Tissue Regeneration in Mammals Is Associated With Reduced Inflammatory Cytokines and an Influx of T Cells

While mammals tend to repair injuries, other adult vertebrates like salamanders and fish regenerate damaged tissue. One prominent hypothesis offered to explain an inability to regenerate complex tissue in mammals is a bias during healing toward strong adaptive immunity and inflammatory responses. Here we directly test this hypothesis by characterizing part of the immune response during regeneration in spiny mice (Acomys cahirinus and Acomys percivali) vs. fibrotic repair in Mus musculus. By directly quantifying cytokines during tissue healing, we found that fibrotic repair was associated with a greater release of pro-inflammatory cytokines (i.e., IL-6, CCL2, and CXCL1) during acute inflammation in the wound microenvironment. However, reducing inflammation via COX-2 inhibition was not sufficient to reduce fibrosis or induce a regenerative response, suggesting that inflammatory strength does not control how an injury heals. Although regeneration was associated with lower concentrations of many inflammatory markers, we measured a comparatively larger influx of T cells into regenerating ear tissue and detected a local increase in the T cell associated cytokines IL-12 and IL-17 during the proliferative phase of regeneration. Taken together, our data demonstrate that a strong adaptive immune response is not antagonistic to regeneration and that other mechanisms likely explain the distribution of regenerative ability in vertebrates.

Oncofetal gene SALL4 reactivation by hepatitis B virus counteracts miR-200c in PD-L1-induced T cell exhaustion

A chronic viral or tumor microenvironment can push T cells to exhaustion by promoting coinhibitory ligand expression. However, how host factors control coinhibitory ligand expression and whether viral infection breaks this control during tumor progress is unknown. Here we show a close negative correlation between SALL4 or PD-L1 and miR-200c in tumors from 98 patients with HBV-related hepatocellular carcinoma. SALL4 or PD-L1 expression correlates negatively with miR-200c expression, and patients with lower levels of SALL4 or PD-L1 and higher miR-200c survive longer. Moreover, over-expression of miR-200c antagonizes HBV-mediated PD-L1 expression by targeting 3'-UTR of CD274 (encoding PD-L1) directly, and reverses antiviral CD8⁺ T cell exhaustion. MiR-200c transcription is inhibited by oncofetal protein SALL4, which is re-expressed through HBV-induced STAT3 activation in adulthood. We propose that an HBV-pSTAT3-SALL4-miR-200c axis regulates PD-L1. Therapeutic strategies to influence this axis might reverse virus-induced immune exhaustion.

Sal-like 4 protein levels in breast cancer cells are post-translationally down-regulated by tripartite motif-containing 21

Sal-like 4 (SALL4) is a transcription factor that enhances proliferation and migration in breast cancer cells. SALL4 expression therefore has the potential to promote cancer malignancy. However, the regulatory mechanisms involved in SALL4 protein expression have not been thoroughly elucidated. In this study, we observed that treating MCF-7 and SUM159 breast cancer cell lines with a proteasome inhibitor increases SALL4 protein levels, suggesting that SALL4 is degraded by the ubiquitin-proteasome system. Using immunoprecipitation to uncover SALL4-binding proteins, we identified an E3 ubiquitin-protein ligase, tripartite motif-containing 21 (TRIM21). Using an EGFP reporter probe of the major SALL4 isoform SALL4B, we observed that shRNA-mediated knockdown of TRIM21 increases cellular SALL4B levels. Immunostaining experiments revealed that TRIM21 localizes to the nucleus, and a K64R substitution in the nuclear localization motif in SALL4B increased SALL4B levels in the cytoplasm. These results suggested that TRIM21 is involved in nuclear SALL4 degradation. To identify the amino acid residue that is targeted by TRIM21, we fragmented the SALL4B sequence, fused it to EGFP, and identified Lys-190 in SALL4B as TRIM21's target residue. Amino acid sequence alignments of SALL family members indicated that the region around SALL4 Lys-190 is conserved in both SALL1 and SALL3. Because SALL1 and SALL4 have similar functions, we constructed a SALL1-EGFP probe and found that the TRIM21 knockdown increases SALL1 levels, indicating that TRIM21 degrades both SALL1 and SALL4. Our findings extend our understanding of SALL4 and SALL1 regulation and may contribute to the development of SALL4-targeting therapies.

SALL4 - KHDRBS3 network enhances stemness by modulating CD44 splicing in basal-like breast cancer

Understanding the mechanism by which cancer cells enhance stemness facilitates cancer therapies. Here, we revealed that a stem cell transcription factor, SALL4, functions to enhance stemness in basal-like breast cancer cells. We used shRNA-mediated knockdown and gene overexpression systems to analyze gene functions. To evaluate stemness, we performed a sphere formation assay. In SALL4 knockdown cells, the sphere formation ability was reduced, indicating that SALL4 enhances stemness. CD44 is a membrane protein and is known as a stemness factor in cancer. CD44 splicing variants are involved in cancer stemness. We discovered that SALL4 modulates CD44 alternative splicing through the upregulation of KHDRBS3, a splicing factor for CD44. We cloned the KHDRBS3-regulated CD44 splicing isoform (CD44v), which lacks exons 8 and 9. CD44v overexpression prevented a reduction in the sphere formation ability by KHDRBS3 knockdown, indicating that CD44v is positively involved in cancer stemness. In addition, CD44v enhanced anoikis resistance under the control of the SALL4 - KHDRBS3 network. Basal-like breast cancer is an aggressive subtype among breast cancers, and there is no effective therapy so far. Our findings provide molecular targets for basal-like breast cancer therapy. In the future, this study may contribute to the establishment of drugs targeting cancer stemness.

DNA demethylation induces SALL4 gene re-expression in subgroups of hepatocellular carcinoma associated with Hepatitis B or C virus infection

Sal-like protein 4 (SALL4), an embryonic stem cell transcriptional regulator, is re-expressed by an unknown mechanism in poor prognosis hepatocellular carcinoma (HCC), often associated with chronic hepatitis B virus (HBV) infection. Herein, we investigated the mechanism of SALL4 re-expression in HBV-related HCCs. We performed bisulfite sequencing PCR of genomic DNA isolated from HBV-related HCCs and HBV replicating cells, and examined DNA methylation of a CpG island located downstream from SALL4 transcriptional start site (TSS). HBV-related HCCs expressing increased SALL4 exhibited demethylation of specific CpG sites downstream of SALL4 TSS. Similarly, SALL4 re-expression and demethylation of these CpGs was observed in HBV replicating cells. SALL4 is also re-expressed in poor prognosis HCCs of other etiologies. Indeed, increased SALL4 expression in hepatitis C virus-related HCCs correlated with demethylation of these CpG sites. To understand how CpG demethylation downstream of SALL4 TSS regulates SALL4 transcription, we quantified by chromatin immunoprecipitation (ChIP) assays RNA polymerase II occupancy of SALL4 gene, as a function of HBV replication. In absence of HBV replication, RNA polymerase II associated with SALL4 exon1. By contrast, in HBV replicating cells RNA polymerase II occupancy of all SALL4 exons increased, suggesting CpG demethylation downstream from SALL4 TSS influences SALL4 transcriptional elongation. Intriguingly, demethylated CpGs downstream from SALL4 TSS are within binding sites of octamer-binding transcription factor 4 (OCT4) and signal transducer and activator of transcription3 (STAT3). ChIP assays confirmed occupancy of these sites by OCT4 and STAT3 in HBV replicating cells, and sequential ChIP assays demonstrated co-occupancy with chromatin remodeling BRG1/Brahma-associated factors. BRG1 knockdown reduced SALL4 expression, whereas BRG1 overexpression increased SALL4 transcription in HBV replicating cells. We conclude demethylation of CpGs located within OCT4 and STAT3 cis-acting elements, downstream of SALL4 TSS, enables OCT4 and STAT3 binding, recruitment of BRG1, and enhanced RNA polymerase II elongation and SALL4 transcription.

The Sal-like 4 - integrin α6β1 network promotes cell migration for metastasis via activation of focal adhesion dynamics in basal-like breast cancer cells

During metastasis, cancer cell migration is enhanced. However, the mechanisms underlying this process remain elusive. Here, we addressed this issue by functionally analyzing the transcription factor Sal-like 4 (SALL4) in basal-like breast cancer cells. Loss-of-function studies of SALL4 showed that this transcription factor is required for the spindle-shaped morphology and the enhanced migration of cancer cells. SALL4 also up-regulated integrin gene expression. The impaired cell migration observed in SALL4 knockdown cells was restored by overexpression of integrin α6 and β1. In addition, we clarified that integrin α6 and β1 formed a heterodimer. At the molecular level, loss of the SALL4 - integrin α6β1 network lost focal adhesion dynamics, which impairs cell migration. Over-activation of Rho is known to inhibit focal adhesion dynamics. We observed that SALL4 knockdown cells exhibited over-activation of Rho. Aberrant Rho activation was suppressed by integrin α6β1 expression, and pharmacological inhibition of Rho activity restored cell migration in SALL4 knockdown cells. These results indicated that the SALL4 - integrin α6β1 network promotes cell migration via modulation of Rho activity. Moreover, our zebrafish metastasis assays demonstrated that this gene network enhances cell migration in vivo. Our findings identify a potential new therapeutic target for the prevention of metastasis, and provide an improved understanding of cancer cell migration.

Importance of SALL4 in the development and prognosis of hepatocellular carcinoma

AIM: To detect the expression of sal-like protein 4 (SALL4) and to explore its relationship with clinicopathological characteristics and prognosis of hepatocellular carcinoma (HCC).

METHODS: One hundred and twenty-six samples of HCC tissue, 44 of adjacent noncancerous cirrhotic tissue and 10 of liver hemangioma tissue, were obtained from patients who underwent hepatectomy for HCC at the Fourth Hospital of Hebei Medical University. None of the patients had received any form of treatment before the operation. After resection, all the tissues were fixed in 10% neutral formaldehyde and embedded in paraffin. Expression of SALL4 was detected by immunohistochemistry. Patients were followed up for postoperative survival until February 2014. The relationships between SALL4 expression level and clinicopathological data and prognosis of HCC were analyzed.

RESULTS: SALL4 expression was negative in the 10 samples of tissue from liver hemangioma, was weakly positive in the two samples from adjacent noncancerous cirrhotic tissue, and positive in 58 samples of HCC tissues. The differences were statistically significant (P < 0.05). Expression of SALL4 was higher in patients with higher α-fetoprotein (AFP) levels, portal vein tumor thrombus, and later clinical stage based on the Barcelona Clinic Liver Cancer classification (P < 0.05). Among patients with negative expression, weakly positive expression, positive expression, and strongly positive expression of SALL4, the median survival time was 39, 25, 23, and 9 mo, respectively (P < 0.001). When both AFP and SALL4 were detected, patients who were negative for both AFP and SALL4, SALL4-positive only, AFP-positive only, and positive for both AFP and SALL4, had a median survival time of 41, 38, 31, and 12 mo, respectively (P < 0.001).

CONCLUSION: Expression of SALL4 is relevant to the prognosis of HCC patients. Patients with higher expression levels of SALL4 and AFP have worse prognosis.

Knockdown of SALL4 inhibits the proliferation and reverses the resistance of MCF-7/ADR cells to doxorubicin hydrochloride

Background

Breast cancer is the most frequent malignancy in women and drug resistance is the major obstacle for its successful chemotherapy. In the present study, we analyzed the involvement of an oncofetal gene, sal-like 4 (SALL4), in the tumor proliferation and drug resistance of human breast cancer.

Results

Our study showed that SALL4 was up-regulated in the drug resistant breast cancer cell line, MCF-7/ADR, compared to the other five cell lines. We established the lentiviral system expressing short hairpin RNA to knockdown SALL4 in MCF-7/ADR cells. Down-regulation of SALL4 inhibited the proliferation of MCF-7/ADR cells and induced the G1 phase arrest in cell cycle, accompanied by an obvious reduction of the expression of cyclinD1 and CDK4. Besides, down-regulating SALL4 can re-sensitize MCF-7/ADR to doxorubicin hydrochloride (ADMh) and had potent synergy with ADMh in MCF-7/ADR cells. Depletion of SALL4 led to a decrease in IC50 for ADMh and an inhibitory effect on the ability to form colonies in MCF-7/ADR cells. With SALL4 knockdown, ADMh accumulation rate of MCF-7/ADR cells was increased, while the expression of BCRP and c-myc was significantly decreased. Furthermore, silencing SALL4 also suppressed the growth of the xenograft tumors and reversed their resistance to ADMh in vivo.

Conclusion

SALL4 knockdown inhibits the growth of the drug resistant breast cancer due to cell cycle arrest and reverses tumor chemo-resistance through down-regulating the membrane transporter, BCPR. Thus, SALL4 has potential as a novel target for the treatment of breast cancer.

SALL4, the missing link between stem cells, development and cancer

There is a growing body of evidence supporting that cancer cells share many similarities with embryonic stem cells (ESCs). For example, aggressive cancers and ESCs share a common gene expression signature that includes hundreds of genes. Since ESC genes are not present in most adult tissues, they could be ideal candidate targets for cancer-specific diagnosis and treatment. This is an exciting cancer-targeting model. The major hurdle to test this model is to identify the key factors/pathway(s) within ESCs that are responsible for the cancer phenotype. SALL4 is one of few genes that can establish this link. The first publication of SALL4 is on its mutation in a human inherited disorder with multiple developmental defects. Since then, over 300 papers have been published on various aspects of this gene in stem cells, development, and cancers. This review aims to summarize our current knowledge of SALL4, including a SALL4-based approach to classify and target cancers. Many questions about this important gene still remain unanswered, specifically, on how this gene regulates cell fates at a molecular level. Understanding SALL4's molecular functions will allow development of specific targeted approaches in the future.

Notch1-STAT3-ETBR signaling axis controls reactive astrocyte proliferation after brain injury

Defining the signaling network that controls reactive astrogliosis may provide novel treatment targets for patients with diverse CNS injuries and pathologies. We report that the radial glial cell antigen RC2 identifies the majority of proliferating glial fibrillary acidic protein-positive (GFAP(+)) reactive astrocytes after stroke. These cells highly expressed endothelin receptor type B (ETB(R)) and Jagged1, a Notch1 receptor ligand. To study signaling in adult reactive astrocytes, we developed a model based on reactive astrocyte-derived neural stem cells isolated from GFAP-CreER-Notch1 conditional knockout (cKO) mice. By loss- and gain-of-function studies and promoter activity assays, we found that Jagged1/Notch1 signaling increased ETB(R) expression indirectly by raising the level of phosphorylated signal transducer and activator of transcription 3 (STAT3), a previously unidentified EDNRB transcriptional activator. Similar to inducible transgenic GFAP-CreER-Notch1-cKO mice, GFAP-CreER-ETB(R)-cKO mice exhibited a defect in reactive astrocyte proliferation after cerebral ischemia. Our results indicate that the Notch1-STAT3-ETB(R) axis connects a signaling network that promotes reactive astrocyte proliferation after brain injury.

CpG signalling, H2A.Z/H3 acetylation and microRNA-mediated deferred self-attenuation orchestrate foetal NOS3 expression

BACKGROUND

An adverse intrauterine environment leads to permanent physiological changes including vascular tone regulation, potentially influencing the risk for adult vascular diseases. We therefore aimed to monitor responsive NOS3 expression in human umbilical artery endothelial cells (HUAEC) and to study the underlying epigenetic signatures involved in its regulation.

RESULTS

NOS3 and STAT3 mRNA levels were elevated in HUAEC of patients who suffered from placental insufficiency. 5-hydroxymethylcytosine, H3K9ac and Histone 2A (H2A).Zac at the NOS3 transcription start site directly correlated with NOS3 mRNA levels. Concomitantly, we observed entangled histone acetylation patterns and NOS3 response upon hypoxic conditions in vitro. Knock-down of either NOS3 or STAT3 by RNAi provided evidence for a functional NOS3/STAT3 relationship. Moreover, we recognized massive turnover of Stat3 at a discrete binding site in the NOS3 promoter. Interestingly, induced hyperacetylation resulted in short-termed increase of NOS3 mRNA followed by deferred decrease indicating that NOS3 expression could become self-attenuated by co-expressed intronic 27 nt-ncRNA. Reporter assay results and phylogenetic analyses enabled us to propose a novel model for STAT3-3'-UTR targeting by this 27-nt-ncRNA.

CONCLUSIONS

An adverse intrauterine environment leads to adaptive changes of NOS3 expression. Apparently, a rapid NOS3 self-limiting response upon ectopic triggers co-exists with longer termed expression changes in response to placental insufficiency involving differential epigenetic signatures. Their persistence might contribute to impaired vascular endothelial response and consequently increase the risk of cardiovascular disease later in life.

Stat3-Efemp2a modulates the fibrillar matrix for cohesive movement of prechordal plate progenitors

Recently, emerging evidence has shown that Stat3 controls tumor cell migration and invasion. However, the molecular mechanisms by which Stat3 controls the cell movement remain largely unknown. Embryonic gastrula progenitors display coordinated and orientated migration, called collective cell migration. Collective cell migration is the simultaneous movement of multiple cells and is universally involved in physiological and pathological programs. Stat3 activity is required for the migration of gastrula progenitors, but it does not affect cell specification, thus suggesting that gastrula movements are an excellent model to provide insight into Stat3 control of cell migration in vivo. In this study, we reveal a novel mechanism by which Stat3 modulates extracellular matrix (ECM) assembly to control the coherence of collective migration of prechordal plate progenitors during zebrafish embryonic gastrulation. We show that Stat3 regulates the expression of Efemp2a in the prechordal plate progenitors that migrate anteriorly during gastrulation. Alteration of Stat3-Efemp2a signaling activity disrupted the configuration of fibronectin (FN) and laminin (LM) matrices, resulting in defective coherence of prechordal plate progenitor movements in zebrafish embryos. We demonstrate that Efemp2a acts as a downstream effector of Stat3 to promote ECM configuration for coherent collective cell migrations in vivo.

The next new target in leukemia: The embryonic stem cell gene SALL4

The embryonic stem (ES) cell gene SALL4 has recently been identified as a new target for cancer therapy, including leukemia. SALL4 is expressed in ES cells and during embryonic development, but is absent in most adult tissues. It is, however, aberrantly expressed in various solid tumors and hematologic malignancies such as myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). Aberrant expression of SALL4 is frequently associated with a more aggressive cancer phenotype, which includes high-risk MDS and its progression to AML. SALL4 contributes to leukemogenesis through multiple pathways including the repression of PTEN and the activation of HOXA9 expression. Targeting the SALL4/PTEN pathway by blocking the protein–protein interaction of SALL4 and its associated epigenetic complex, nucleosome remodeling and deacetylase complex (NuRD), might be a novel approach to treating AML and holds great potential for the treatment of other SALL4-mediated oncogenic processes such as high-risk MDS and solid tumors.

SALL4: an emerging cancer biomarker and target

SALL4 is a transcription factor that plays essential roles in maintaining self-renewal and pluripotency of embryonic stem cells (ESCs). In fully differentiated cells, SALL4 expression is down-regulated or silenced. Accumulating evidence suggest that SALL4 expression is reactivated in cancer. Constitutive expression of SALL4 transgene readily induces acute myeloid leukemia (AML) development in mice. Gain- and loss-of-function studies reveal that SALL4 regulates proliferation, apoptosis, invasive migration, chemoresistance, and the maintenance of cancer stem cells (CSCs). SALL4 controls the expression of its downstream genes through both genetic and epigenetic mechanisms. High level of SALL4 expression is detected in cancer patients, which predicts adverse progression and poor outcome. Moreover, targeted inhibition of SALL4 has shown efficient therapeutic effects on cancer. We have summarized the recent advances in the biology of SALL4 with a focus on its role in cancer. Further study of the oncogenic functions of SALL4 and the underlying molecular mechanisms will shed light on cancer biology and provide new implications for cancer diagnostics and therapy.

Regulation of PSMB5 protein and β subunits of mammalian proteasome by constitutively activated signal transducer and activator of transcription 3 (STAT3): potential role in bortezomib-mediated anticancer therapy

The ubiquitin-proteasome system facilitates the degradation of ubiquitin-tagged proteins and performs a regulatory role in cells. Elevated proteasome activity and subunit expression are found in several cancers. However, the inherent molecular mechanisms responsible for increased proteasome function in cancers remain unclear despite the well investigated and defined role of the mammalian proteasome. This study was initiated to elucidate the mechanisms involved in the regulation of β subunits of the mammalian proteasome. Suppression of STAT3 tyrosine phosphorylation coordinately decreased the mRNA and protein levels of the β subunits of the 20 S core complex in DU145 cells. Notably, PSMB5, a molecular target of bortezomib, was shown to be a target of STAT3. Knockdown of STAT3 decreased PSMB5 protein. Inhibition of phospho-STAT3 substantially reduced PSMB5 protein levels in cells expressing constitutively active-STAT3. Accumulation of activated STAT3 resulted in the induction of PSMB5 promoter and protein levels. In addition, a direct correlation was observed between the endogenous levels of PSMB5 and constitutively active STAT3. PSMB5 and STAT3 protein levels remained unaltered following the inhibition of proteasome activity. The EGF-induced concerted increase of β subunits was blocked by inhibition of the EGF receptor or STAT3 but not by the PI3K/AKT or MEK/ERK pathways. Decreased proteasome activities were due to reduced protein levels of catalytic subunits of the proteasome in STAT3-inhibited cells. Combined treatments with bortezomib and inhibitor of STAT3 abrogated proteasome activity and enhanced cellular apoptosis. Overall, we demonstrate that aberrant activation of STAT3 regulates the expression of β subunits, in particular PSMB5, and the catalytic activity of the proteasome.

Jumonji domain-containing protein 2B silencing induces DNA damage response via STAT3 pathway in colorectal cancer

Background:

Jumonji domain-containing protein 2B (JMJD2B), directly targeted by hypoxia-inducible factor 1α, maintains the histone methylation balance important for the transcriptional activation of many oncogenes. Jumonji domain-containing protein 2B has been implicated in colorectal cancer (CRC) progression; however, the mechanism remains unclear.

Methods:

Immunofluorescence and western blotting detected phosphorylated histone H2AX, characteristic of double-strand breaks, and comet assay was used to investigate DNA damage, in CRC cells after JMJD2B small interfering RNA (siRNA) transfection. We assessed the resulting in vitro responses, that is, cell cycle progression, apoptosis, and senescence coupled with JMJD2B silencing-induced DNA damage, studying the regulatory role of signal transducers and activators of transcription 3 (STAT3). The JMJD2B silencing anti-cancer effect was determined using an in vivo CRC xenograft model.

Results:

Jumonji domain-containing protein 2B knockdown induced DNA damage via ataxia telangiectasia-mutated (ATM) and ATM and Rad3-related pathway activation, resulting in cell cycle arrest, apoptosis, and senescence in both normoxia and hypoxia. Signal transducers and activators of transcription 3 suppression by JMJD2B silencing enhanced DNA damage. Intratumoural injection of JMJD2B siRNA suppressed tumour growth in vivo and activated the DNA damage response (DDR).

Conclusions:

Jumonji domain-containing protein 2B has an essential role in cancer cell survival and tumour growth via DDR mediation, which STAT3 partially regulates, suggesting that JMJD2B is a potential anti-cancer target.

SALL4, a novel marker for human gastric carcinogenesis and metastasis

SALL4, a zinc-finger transcriptional factor for embryonic stem cell self-renewal and pluripotency, has been suggested to be involved in tumorigenesis. The role of SALL4 in human gastric cancer, however, remains largely unknown. In this study, we demonstrated that SALL4 was aberrantly expressed at both mRNA and protein levels in human gastric cancer tissues, and SALL4 level was highly correlated with lymph node metastasis. Enforced expression of SALL4 enhanced the proliferation and migration of human gastric cancer cells, whereas knockdown of SALL4 by siRNA led to the opposite effects. In addition, SALL4 overexpression promoted the growth and metastasis of gastric xenograft tumor in vivo. SALL4 overexpression induced epithelial-mesenchymal transition (EMT) in gastric cancer cells, with increased expression of Twist1, N-cadherin and decreased expression of E-cadherin. Moreover, SALL4 promoted the acquirement of stemness in gastric cancer cells through the induction of Bmi-1 and Lin28B. Taken together, our findings indicate that SALL4 has oncogenic roles in gastric cancer through the modulation of EMT and cell stemness, suggesting SALL4 as a novel target for human gastric cancer diagnosis and therapy.

Sal-like 4 (SALL4) suppresses CDH1 expression and maintains cell dispersion in basal-like breast cancer

In cell cultures, the dispersed phenotype is indicative of the migratory ability. Here we characterized Sal-like 4 (SALL4) as a dispersion factor in basal-like breast cancer. Our shRNA-mediated SALL4 knockdown system and SALL4 overexpression system revealed that SALL4 suppresses the expression of adhesion gene CDH1, and positively regulates the CDH1 suppressor ZEB1. Cell behavior analyses showed that SALL4 suppresses intercellular adhesion and maintains cell motility after cell-cell interaction and cell division, which results in the dispersed phenotype. Our findings indicate that SALL4 functions to suppress CDH1 expression and to maintain cell dispersion in basal-like breast cancer.

Low-expression of microRNA-107 inhibits cell apoptosis in glioma by upregulation of SALL4

Glioma is the most common highly malignant primary brain tumor. The molecular pathways that result in the pathogenesis of glioma remain elusive. In this study, we found microRNA-107 (miR-107) was downregulated in glioma tissues and cell lines. Our results revealed miR-107 overexpression suppressed cell proliferation in glioma cells, whereas miR-107 knockdown promoted cell growth in MO59K. miR-107 expression induced apoptosis in glioma cells possibly through the increase in Fas (TNFRSF6)-associated via death domain (FADD) expression and activation of caspases-8 and -3/7. Moreover, the activity of caspase-8 in miR-107-overexpressing SHG44 cells was suppressed with FADD knockdown. The tumor growth in nude mice bearing miR-107-overexpressing SHG44 cells was blocked through apoptosis induction. Sal-like 4 (Drosophila) (SALL4) level was reduced upon miR-107 overexpression in glioma cells, and the inverse was observed upon miR-107 knockdown in MO59K. Using a luciferase reporter system, SALL4 3'-UTR-dependent luciferase activity was reduced by miR-107 mimics or increased by an inhibitor of miR-107. In SHG44, SALL4 downregulation triggered growth inhibition and activated FADD-mediated cell apoptosis pathway. The caspase-8 activity in miR-107-overexpressing SHG44 cells was suppressed with SALL4 upregulation. Furthermore, primary glioma tumors with low miR-107 expression show elevated SALL4 level. An obvious inverse correlation was observed between miR-107 expression and SALL4 level in clinical glioma samples. Therefore, our results demonstrate upregulation of miR-107 suppressed glioma cell growth through direct targeting of SALL4, leading to the activation of FADD/caspase-8/caspase-3/7 signaling pathway of cell apoptosis. These data suggest miR-107 is a potential therapeutic target against glioma.

Sal-like protein 4 (SALL4), a stem cell biomarker in liver cancers

Liver cancers, including hepatocellular carcinomas (HCCs), cholangiocarcinomas (CCs), and fibrolamellar HCCs (FL-HCCs) are among the most common cancers worldwide and are associated with a poor prognosis. Investigations of genes important in liver cancers have focused on Sal-like protein 4 (SALL4), a member of a family of zinc finger transcription factors. It is a regulator of embryogenesis, organogenesis, pluripotency, can elicit reprogramming of somatic cells, and is a marker of stem cells. We found it expressed in normal murine hepatoblasts, normal human hepatic stem cells, hepatoblasts and biliary tree stem cells, but not in mature parenchymal cells of liver or biliary tree. It was strongly expressed in surgical specimens of human HCCs, CCs, a combined hepatocellular and cholangiocarcinoma, a FL-HCC, and in derivative, transplantable tumor lines in immune-compromised hosts. Bioinformatics analyses indicated that elevated expression of SALL4 in tumors is associated with poor survival of HCC patients. Experimental manipulation of SALL4's expression results in changes in proliferation versus differentiation in human HCC cell lines in vitro and in vivo in immune-compromised hosts. Virus-mediated gene transfer of SALL4 was used for gain- and loss-of-function analyses in the cell lines. Significant growth inhibition in vitro and in vivo, accompanied by an increase in differentiation occurred with down-regulation of SALL4. Overexpression of SALL4 resulted in increased cell proliferation in vitro, correlating with an increase in expression of cytokeratin19 (CK19), epithelial cell adhesion molecules (EpCAM), and adenosine triphosphate (ATP)-binding cassette-G2 (ABCG2).

CONCLUSION

SALL4's expression is an indicator of stem cells, a prognostic marker in liver cancers, correlates with cell and tumor growth, with resistance to 5-FU, and its suppression results in differentiation and slowed tumor growth. SALL4 is a novel therapeutic target for liver cancers.

Prediction and experimental validation of a putative non-consensus binding site for transcription factor STAT3 in serum amyloid A gene promoter

We previously demonstrated that though the human SAA1 gene shows no typical STAT3 response element (STAT3-RE) in its promoter region, STAT3 and the nuclear factor (NF-κB) p65 first form a complex following interleukin IL-1 and IL-6 (IL-1+6) stimulation, after which STAT3 interacts with a region downstream of the NF-κB RE in the SAA1 promoter. In this study, we employed a computational approach based on indirect read outs of protein-DNA contacts to identify a set of candidates for non-consensus STAT3 transcription factor binding sites (TFBSs). The binding of STAT3 to one of the predicted non-consensus TFBSs was experimentally confirmed through a dual luciferase assay and DNA affinity chromatography. The present study defines a novel STAT3 non-consensus TFBS at nt -75/-66 downstream of the NF-κB RE in the SAA1 promoter region that is required for NF-κB p65 and STAT3 to activate SAA1 transcription in human HepG2 liver cells. Our analysis builds upon the current understanding of STAT3 function, suggesting a wider array of mechanisms of STAT3 function in inflammatory response, and provides a useful framework for investigating novel TF-target associations with potential therapeutic implications.

Targeting transcription factor SALL4 in acute myeloid leukemia by interrupting its interaction with an epigenetic complex

An exciting recent approach to targeting transcription factors in cancer is to block formation of oncogenic complexes. We investigated whether interfering with the interaction of the transcription factor SALL4, which is critical for leukemic cell survival, and its epigenetic partner complex represents a novel therapeutic approach. The mechanism of SALL4 in promoting leukemogenesis is at least in part mediated by its repression of the tumor suppressor phosphatase and tensin homolog deleted on chromosome 10 (PTEN) through its interaction with a histone deacetylase (HDAC) complex. In this study, we demonstrate that a peptide can compete with SALL4 in interacting with the HDAC complex and reverse its effect on PTEN repression. Treating SALL4-expressing malignant cells with this peptide leads to cell death that can be rescued by a PTEN inhibitor. The antileukemic effect of this peptide can be confirmed on primary human leukemia cells in culture and in vivo, and is identical to that of down-regulation of SALL4 in these cells using an RNAi approach. In summary, our results demonstrate a novel peptide that can block the specific interaction between SALL4 and its epigenetic HDAC complex in regulating its target gene, PTEN. Furthermore, targeting SALL4 with this approach could be an innovative approach in treating leukemia.

The role of stem cell factor SALL4 in leukemogenesis

SALL4, a member of the SALL gene family, is one of the most important transcriptional regulators of stem cells. It is of particular interest to stem cell biologists because it is linked to the self-renewal of both embryonic stem cells (ESCs) and hematopoietic stem cells (HSCs), and it is involved in human leukemia. In ESCs, the Sall4/Oct4/Nanog core transcriptional network governs the self-renewal and pluripotent properties of human and murine ESCs. In normal HSCs and leukemic stem cells (LSCs), SALL4 is linked to three known pathways that are involved in self-renewal: Wnt/β-catenin, Bmi-1, and Pten. Despite the important shared role of SALL4 in self-renewal of HSCs and LSCs, our recent studies obtained through correlating global downstream target genes and unique functional studies in normal versus leukemic cells have demonstrated that SALL4 has differential effects on both pro- and anti-apoptotic pathways in normal and leukemic cells. Targeting SALL4, particularly when combined with the use of ABT-737, a BCL2 antagonist, could lead to leukemic cell-specific apoptosis. This review summarizes our current knowledge on the SALL gene family development, particularly on the role of SALL4 in stem cells, as well as tumorigenesis, especially leukemogenesis.

SALL4, a stem cell factor, affects the side population by regulation of the ATP-binding cassette drug transport genes

Our previous work shows that the stem cell factor SALL4 plays a central role in embryonic and leukemic stem cells. In this study, we report that SALL4 expression was higher in drug resistant primary acute myeloid leukemic patients than those from drug-responsive cases. In addition, while overexpression of SALL4 led to drug resistance in cell lines, cells with decreased SALL4 expression were more sensitive to drug treatments than the parental cells. This led to our investigation of the implication of SALL4 in drug resistance and its role in side population (SP) cancer stem cells. SALL4 expression was higher in SP cells compared to non-SP cells by 2-4 fold in various malignant hematopoietic cell lines. Knocking down of SALL4 in isolated SP cells resulted in a reduction of SP cells, indicating that SALL4 is required for their self-renewal. The SP phenotype is known to be mediated by members of the ATP-binding cassette (ABC) drug transport protein family, such as ABCG2 and ABCA3. Using chromatin-immunoprecipitation (ChIP), quantitative reverse transcription polymerase chain reaction (qRT-PCR) and electrophoretic mobility shift assay(EMSA), we demonstrated that SALL4 was able to bind to the promoter region of ABCA3 and activate its expression while regulating the expression of ABCG2 indirectly. Furthermore, SALL4 expression was positively correlated to those of ABCG2 and ABCA3 in primary leukemic patient samples. Taken together, our results suggest a novel role for SALL4 in drug sensitivity, at least in part through the maintenance of SP cells, and therefore may be responsible for drug-resistance in leukemia. We are the first to demonstrate a direct link between stem cell factor SALL4, SP and drug resistance in leukemia.

Transcriptional and post-translational regulation of the quiescence factor and putative tumor suppressor p150(Sal2)

The evolutionarily conserved SALL genes encode transcription factors with roles in embryonic development. The product of the SALL2 gene was first identified as a binding partner of the mouse polyoma virus large T antigen and later shown to possess tumor suppressor-like functions. Independent studies identified SALL2 as a factor regulating the quiescent state in human fibroblasts. Here, we investigate factors that regulate the expression of SALL2 and turnover of p150(Sal2) in growing vs. resting cells. The transcription factor AP4 increases along with SALL2 in quiescent cells and positively regulates SALL2 expression. TGFβ effectively inhibits expression of SALL2 and its regulator AP4 when added to quiescent fibroblasts. TGFβ repression of SALL2 and AP4 is independent of the induction of connective tissue growth factor (CTGF) by TGFβ. p150(Sal2) disappears rapidly on restoration of serum. In both growing fibroblasts and established ovarian surface epithelial cells, p150(Sal2) undergoes polyubiquitination and proteosomal degradation. A CUL4/DDB1 E3 ligase containing RBBP7 as the p150(Sal2) receptor has been identified as mediating the destruction of p150(Sal2) as cells transition from a quiescent to an actively growing state.