The tumor suppressor protein p150Sal2 in carcinogenesis

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.

CRISPR-mediated promoter de/methylation technologies for gene regulation

DNA methylation on cytosines of CpG dinucleotides is well established as a basis of epigenetic regulation in mammalian cells. Since aberrant regulation of DNA methylation in promoters of tumor suppressor genes or proto-oncogenes may contribute to the initiation and progression of various types of human cancer, sequence-specific methylation and demethylation technologies could have great clinical benefit. The CRISPR-Cas9 protein with a guide RNA can target DNA sequences regardless of the methylation status of the target site, making this system superb for precise methylation editing and gene regulation. Targeted methylation-editing technologies employing the dCas9 fusion proteins have been shown to be highly effective in gene regulation without altering the DNA sequence. In this review, we discuss epigenetic alterations in tumorigenesis as well as various dCas9 fusion technologies and their usages in site-specific methylation editing and gene regulation.

SALL2 Is a Novel Prognostic Methylation Marker in Patients with Oral Squamous Carcinomas: Associations with SALL1 and SALL3 Methylation Status

Staging and pathological grading systems are convenient, but imperfect predictors of recurrence of head and neck squamous cell carcinoma. Therefore, to identify potential alternative prognostic markers, we investigated the methylation status of the promoter of Sal-like protein 2 (SALL2). SALL2 mRNA expression was absent in 8/9 (88.9%) University of Michigan squamous cell carcinoma cell lines, whereas two nonmalignant cell lines had stable expression. The normalized methylation value of SALL2 in cancer cell lines was significantly higher than in normal cell lines. SALL2 methylation found in 74 of 233 (31.8%) tumor specimens was correlated with the methylation status of both SALL1 and SALL3. SALL2 methylation was not associated with any difference in disease-free survival (DFS). Therefore, the presence of SALL2 methylation was statistically correlated with a decrease in DFS in patients with oral cancer (log-rank test, p = 0.032). Furthermore, it was associated with disease recurrence in 36.2% of oral cancer cases, with an odds ratio of 2.922 (95% confidence interval = 1.198-7.130; p = 0.018) by multivariate Cox proportional hazard regression analysis. This study suggests that cytosine-phosphate- guanosine (CpG) hypermethylation is a likely mechanism of SALL2 inactivation and supports the hypothesis that SALL2 could serve as an important clinical risk assessment.

Transcriptomic analysis reveals that BMP4 sensitizes glioblastoma tumor-initiating cells to mechanical cues

The poor prognosis of glioblastoma (GBM) is associated with a highly invasive stem-like subpopulation of tumor-initiating cells (TICs), which drive recurrence and contribute to intra-tumoral heterogeneity through differentiation. These TICs are better able to escape extracellular matrix-imposed mechanical restrictions on invasion than their more differentiated progeny, and sensitization of TICs to extracellular matrix mechanics extends survival in preclinical models of GBM. However, little is known about the molecular basis of the relationship between TIC differentiation and mechanotransduction. Here we explore this relationship through a combination of transcriptomic analysis and studies with defined-stiffness matrices. We show that TIC differentiation induced by bone morphogenetic protein 4 (BMP4) suppresses expression of proteins relevant to extracellular matrix signaling and sensitizes TIC spreading to matrix stiffness. Moreover, our findings point towards a previously unappreciated connection between BMP4-induced differentiation, mechanotransduction, and metabolism. Notably, stiffness and differentiation modulate oxygen consumption, and inhibition of oxidative phosphorylation influences cell spreading in a stiffness- and differentiation-dependent manner. Our work integrates bioinformatic analysis with targeted molecular measurements and perturbations to yield new insight into how morphogen-induced differentiation influences how GBM TICs process mechanical inputs.

mRNA and methylation profiling of radioresistant esophageal cancer cells: the involvement of Sall2 in acquired aggressive phenotypes

Esophageal squamous cell carcinoma (ESCC) is one of the deadliest malignancies worldwide. Radiotherapy plays a critical role in the curative management of inoperable ESCC patients. However, radioresistance restricts the efficacy of radiotherapy for ESCC patients. The molecules involved in radioresistance remain largely unknown, and new approaches to sensitize cells to irradiation are in demand. Technical advances in analysis of mRNA and methylation have enabled the exploration of the etiology of diseases and have the potential to broaden our understanding of the molecular pathways of ESCC radioresistance. In this study, we constructed radioresistant TE-1 and Eca-109 cell lines (TE-1/R and Eca-109/R, respectively). The radioresistant cells showed an increased migration ability but reduced apoptosis and cisplatin sensitivity compared with their parent cells. mRNA and methylation profiling by microarray revealed 1192 preferentially expressed mRNAs and 8841 aberrantly methylated regions between TE-1/R and TE-1 cells. By integrating the mRNA and methylation profiles, we related the decreased expression of transcription factor Sall2 with a corresponding increase in its methylation in TE-1/R cells, indicating its involvement in radioresistance. Upregulation of Sall2 decreased the growth and migration advantage of radioresistant ESCC cells. Taken together, our present findings illustrate the mRNA and DNA methylation changes during the radioresistance of ESCC and the important role of Sall2 in esophageal cancer malignancy.

Roles of SALL2 in tumorigenesis

The proteins p150^Sal2 (product of SALL2) and p53 share growth arrest and pro-apoptotic functions by independently inducing p21^Cip1/Waf1 and BAX, and both proteins are targeted by the human papilloma virus E6 protein, leading to blockage of growth arrest in infected cells. Loss of both p53 and Sall2 in mice causes significantly higher mortality and metastasis rates compared with p53 single mutant mice. Therefore, p150^Sal2 seems to have strong potential as a novel cancer biomarker for early diagnosis and risk prediction. Loss of SALL2 expression is observed in many cases of human serous ovarian carcinoma, whereas normal ovarian epithelial cells maintain high levels of the p150^Sal2 protein, supporting an important tumor suppressive role for p150^Sal2 in the human ovary. In contrast, p150^Sal2 is a transcription factor required to convert differentiated glioblastoma cells into stem-like tumor-propagating cells, suggesting that its functional roles are dependent on tissue types and cellular context. The function of p150^Sal2 in normal and diseased cells and possible therapeutic approaches are discussed in this review.