Leukemic survival factor SALL4 contributes to defective DNA damage repair

SALL4 in gastrointestinal tract cancers: upstream and downstream regulatory mechanisms

Effective therapeutic targets and early diagnosis are major challenges in the treatment of gastrointestinal tract (GIT) cancers. SALL4 is a well-known transcription factor that is involved in organogenesis during embryonic development. Previous studies have revealed that SALL4 regulates cell proliferation, survival, and migration and maintains stem cell function in mature cells. Additionally, SALL4 overexpression is associated with tumorigenesis. Despite its characterization as a biomarker in various cancers, the role of SALL4 in GIT cancers and the underlying mechanisms are unclear. We describe the functions of SALL4 in GIT cancers and discuss its upstream/downstream genes and pathways associated with each cancer. We also consider the possibility of targeting these genes or pathways as potential therapeutic options for GIT cancers.

SALL4 is a CRL3REN/KCTD11 substrate that drives Sonic Hedgehog-dependent medulloblastoma

The Sonic Hedgehog (SHH) pathway is crucial regulator of embryonic development and stemness. Its alteration leads to medulloblastoma (MB), the most common malignant pediatric brain tumor. The SHH-MB subgroup is the best genetically characterized, however the molecular mechanisms responsible for its pathogenesis are not fully understood and therapeutic benefits are still limited. Here, we show that the pro-oncogenic stemness regulator Spalt-like transcriptional factor 4 (SALL4) is re-expressed in mouse SHH-MB models, and its high levels correlate with worse overall survival in SHH-MB patients. Proteomic analysis revealed that SALL4 interacts with REN/KCTD11 (here REN), a substrate receptor subunit of the Cullin3-RING ubiquitin ligase complex (CRL3REN) and a tumor suppressor lost in ~30% of human SHH-MBs. We demonstrate that CRL3REN induces polyubiquitylation and degradation of wild type SALL4, but not of a SALL4 mutant lacking zinc finger cluster 1 domain (ΔZFC1). Interestingly, SALL4 binds GLI1 and cooperates with HDAC1 to potentiate GLI1 deacetylation and transcriptional activity. Notably, inhibition of SALL4 suppresses SHH-MB growth both in murine and patient-derived xenograft models. Our findings identify SALL4 as a CRL3REN substrate and a promising therapeutic target in SHH-dependent cancers.

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.

SALL4 Oncogenic Function in Cancers: Mechanisms and Therapeutic Relevance

SALL4, a member of the SALL family, is an embryonic stem cell regulator involved in self-renewal and pluripotency. Recently, SALL4 overexpression was found in malignant cancers, including lung cancer, hepatocellular carcinoma, breast cancer, gastric cancer, colorectal cancer, osteosarcoma, acute myeloid leukemia, ovarian cancer, and glioma. This review updates recent advances of our knowledge of the biology of SALL4 with a focus on its mechanisms and regulatory functions in tumors and human hematopoiesis. SALL4 overexpression promotes proliferation, development, invasion, and migration in cancers through activation of the Wnt/β-catenin, PI3K/AKT, and Notch signaling pathways; expression of mitochondrial oxidative phosphorylation genes; and inhibition of the expression of the Bcl-2 family, caspase-related proteins, and death receptors. Additionally, SALL4 regulates tumor progression correlated with the immune microenvironment involved in the TNF family and gene expression through epigenetic mechanisms, consequently affecting hematopoiesis. Therefore, SALL4 plays a critical oncogenic role in gene transcription and tumor growth. However, there are still some scientific hypotheses to be tested regarding whether SALL4 is a therapeutic target, such as different tumor microenvironments and drug resistance. Thus, an in-depth understanding and study of the functions and mechanisms of SALL4 in cancer may help develop novel strategies for cancer therapy.

The Study of SALL4 Gene and BMI-1 Gene Expression in Acute Myeloid Leukemia Patients

BACKGROUND

In acute myeloid leukemia (AML), many genes have been studied as prognostic markers. SALL4 is expressed constitutively in human leukemia cell lines and primary AML cells. BMI-1 is expressed highly in purified hematopoietic stem cells (HSCs), and its expression declines with differentiation.

OBJECTIVE

To study the expression levels of SALL4 and BMI-1 and their clinical significance in patients with AML.

METHODS

The study was performed with 60 patients newly diagnosed with AML and 50 control individuals. SALL4 and BMI-1 expression detection were performed using real-time polymerase chain reaction (PCR).

RESULTS

The expression of SALL4 and BMI-1 was significantly higher in cases of AML and showed a strong association with failure to achieve complete remission (CR) or with relapse (P = .02, P = .03, respectively). In multivariate analysis, these genes were the most powerful independent predictors of poor prognosis (P = .01 for SALL4, P = .02 for BMI-1).

CONCLUSION

SALL4 and BMI-1 are significant prognostic factors in AML and could be strong targets for novel types of therapy.

Differential expression of SALL4 in CTCs derived from hydatidiform moles and gestational trophoblastic neoplasms

PROBLEM

To investigate EMT phenotype and SALL4 expression of circulating tumour cells (CTCs) in patients with gestational trophoblastic neoplasm (GTN).

METHOD OF STUDY

CanPatrol CTC detection system in combination with SALL4 RNA in situ hybridization was used to investigate the profile of CTCs in different types of gestational trophoblastic disease (GTD). Circulating CTCs were phenotyped and annotated with SALL4 expression in 41 GTD patients, including 12 HM and 29 GTN, as well as 22 pregnant volunteers.

RESULTS

A positive correlation between the number of CTC and serum β-hCG concentration was found among the GTN patients. The number of E/M-CTC was positively correlated with serum β-hCG, while M-CTC was positively correlated with prognostic score. Comparison among malignant GTD, benign GTD and healthy pregnant women revealed a significant difference in the number of total CTC, E/M-CTC, and M-CTC but not in E-CTC. ROC analysis was conducted to evaluate the performance of CTC phenotypes in distinguishing GTD patients from healthy pregnant women yielding an AUC as 0.826. Youden's index was maximal at the cutoff value of 8.5/4 mL with sensitivity and specificity at 53.66% and 100%, respectively. SALL4 expression was evaluated in GTD patients with CTC count greater than cutoff value. SALL4 high expressing CTCs (>2 signal dots) were detected in 66.67% (10/15) of malignant GTD patients but not in benign patients (0/5).

CONCLUSION

Differential expression of SALL4 was seen in CTCs derived from hydatidiform moles and GTN. CTC profiling may be developed as an adjunct marker to diagnose GTN.

SALL4 Gene Expression in Acute Myeloid Leukemia

OBJECTIVES

SALL4 gene was aberrantly expressed in many leukemia cell lines and primary leukemia cells of acute myeloid leukemia (AML) and precursor B-cell lymphoblastic leukemia/lymphomas. Its expression may be a useful marker to predict the diagnosis and the risk stratification of patients with AML.

METHODS

This study aimed to characterize the expression pattern of SALL4 gene in adult patients with acute myeloid leukemia. Quantitative Real-time PCR was used to determine the expression level of the gene in peripheral blood of 52 Egyptian adult AML patients and 10 healthy control cases. Our study was done in the National Cancer Institute during the period of time between December 2014 and June 2015.

RESULTS

The observed data revealed that none of the studied controls expressed SALL4 > 1.0 RQ and there was a highly statistically significant difference between cases and controls regarding SALL4 gene expression where all cases showed higher expression of SALL4 than controls with p value <0.001.

CONCLUSION

In AML, SALL4 is one of few genes that bridge the self-renewal properties of ESCs, normal HSCs and LSCs. Their expression is easily determined by real time PCR. They may be useful markers to predict prognosis and help to stratify patients into risk adapted groups. Further studies including increasing patient numbers are essential to understand the relations between SALL4 gene expression and its prognostic impact.

Expression pattern and prognostic implication of SALL4 gene in myeloid leukemias: a case-control study

SALL4 is a transcription factor that retains stem cells in an undifferentiated state and promotes its self-renewal. In addition, it is implicated in leukemogenesis via its effect on leukemic stem cells. This study aimed to characterize the expression pattern of SALL4 gene in acute myeloid leukemia (AML) and chronic myeloid leukemia (CML) at different progression phases of the leukemic process and to assess its prognostic significance. Real-time PCR was used in 106 patients: 54 AML patients; 43 de novo and 11 in complete remission (CR), 52 CML patients; 31 in chronic phase (CP), 11 in deep molecular response (MR⁴) and 10 in accelerated/blastic phase (AP/BP); and in 21 nonmalignant bone marrow samples. SALL4 gene expression was elevated in AML, AML-CR and CML-CP (median = 5.180, 4.604 and 14.125 fold changes, respectively). Elevated SALL4 gene expression among AML de novo patient was associated with poor disease-free survival (DFS) rates (p = .022). Among CML patients, the highest percentage of patients with a high SALL4 (p = .033) was among CML-CP. SALL4 has a role in leukemogenesis; high SALL4 expression was associated with poor DFS among AML patients.

The association between preaxial polydactyly and radial longitudinal deficiency in syndromic cases: a report on nine families

Preaxial polydactyly and radial longitudinal deficiency are usually viewed as two different entities. We present nine families with different disorders in which both preaxial polydactyly and radial longitudinal deficiency were seen in the phenotype. This indicates that both entities may be caused by the same developmental error or insult. The pathogenesis is complex and may be related to the interactions of two signalling loops: the first loop (named as the radial longitudinal deficiency loop) contains genes/proteins responsible for the development of the radial ray; and the second loop (named as the preaxial polydactyly loop) contains the Sonic Hedgehog involved in the pathogenesis of preaxial polydactyly. This entity is named as the preaxial polydactyly-radial longitudinal deficiency association and should be included in the description of the preaxial polydactyly spectrum.

LEVEL OF EVIDENCE

IV.

Zone of Polarizing Activity Regulatory Sequence Mutations/Duplications with Preaxial Polydactyly and Longitudinal Preaxial Ray Deficiency in the Phenotype: A Review of Human Cases, Animal Models, and Insights Regarding the Pathogenesis

Clinicians and scientists interested in developmental biology have viewed preaxial polydactyly (PPD) and longitudinal preaxial ray deficiency (LPAD) as two different entities. Point mutations and duplications in the zone of polarizing activity regulatory sequence (ZRS) are associated with anterior ectopic expression of Sonic Hedgehog (SHH) in the limb bud and usually result in a PPD phenotype. However, some of these mutations/duplications also have LPAD in the phenotype. This unusual PPD-LPAD association in ZRS mutations/duplications has not been specifically reviewed in the literature. The author reviews this unusual entity and gives insights regarding its pathogenesis.

SALL4 as a transcriptional and epigenetic regulator in normal and leukemic hematopoiesis

In recent years, there has been substantial progress in our knowledge of the molecular pathways by which stem cell factor SALL4 regulates the embryonic stem cell (ESC) properties, developmental events, and human cancers. This review summarizes recent advances in the biology of SALL4 with a focus on its regulatory functions in normal and leukemic hematopoiesis. In the normal hematopoietic system, expression of SALL4 is mainly enriched in the bone marrow hematopoietic stem/progenitor cells (HSCs/HPCs), but is rapidly silenced following lineage differentiation. In hematopoietic malignancies, however, SALL4 expression is abnormally re-activated and linked with deteriorated disease status in patients. Further, SALL4 activation participates in the pathogenesis of tumor initiation and disease progression. Thus, a better understanding of SALL4's biologic functions and mechanisms will facilitate development of advanced targeted anti-leukemia approaches in future.