Nucleotide alteration of retinoblastoma protein-interacting zinc finger gene, RIZ, in human leukemia

Searching for a Putative Mechanism of RIZ2 Tumor-Promoting Function in Cancer Models

Positive Regulatory Domain (PRDM) gene family members commonly express two main molecular variants, the PR-plus isoform usually acting as tumor suppressor and the PR-minus one functioning as oncogene. Accordingly, PRDM2/RIZ encodes for RIZ1 (PR-plus) and RIZ2 (PR-minus). In human cancers, genetic or epigenetic modifications induce RIZ1 silencing with an expression level imbalance in favor of RIZ2 that could be relevant for tumorigenesis. Additionally, in estrogen target cells and tissues, estradiol increases RIZ2 expression level with concurrent increase of cell proliferation and survival. Several attempts to study RIZ2 function in HeLa or MCF-7 cells by its over-expression were unsuccessful. Thus, we over-expressed RIZ2 in HEK-293 cells, which are both RIZ1 and RIZ2 positive but unresponsive to estrogens. The forced RIZ2 expression increased cell viability and growth, prompted the G2-to-M phase transition and organoids formation. Accordingly, microarray analysis revealed that RIZ2 regulates several genes involved in mitosis. Consistently, RIZ silencing in both estrogen-responsive MCF-7 and -unresponsive MDA-MB-231 cells induced a reduction of cell proliferation and an increase of apoptosis rate. Our findings add novel insights on the putative RIZ2 tumor-promoting functions, although additional attempts are warranted to depict the underlying molecular mechanism.

Multifaceted Role of PRDM Proteins in Human Cancer

The PR/SET domain family (PRDM) comprise a family of genes whose protein products share a conserved N-terminal PR [PRDI-BF1 (positive regulatory domain I-binding factor 1) and RIZ1 (retinoblastoma protein-interacting zinc finger gene 1)] homologous domain structurally and functionally similar to the catalytic SET [Su(var)3-9, enhancer-of-zeste and trithorax] domain of histone methyltransferases (HMTs). These genes are involved in epigenetic regulation of gene expression through their intrinsic HMTase activity or via interactions with other chromatin modifying enzymes. In this way they control a broad spectrum of biological processes, including proliferation and differentiation control, cell cycle progression, and maintenance of immune cell homeostasis. In cancer, tumor-specific dysfunctions of PRDM genes alter their expression by genetic and/or epigenetic modifications. A common characteristic of most PRDM genes is to encode for two main molecular variants with or without the PR domain. They are generated by either alternative splicing or alternative use of different promoters and play opposite roles, particularly in cancer where their imbalance can be often observed. In this scenario, PRDM proteins are involved in cancer onset, invasion, and metastasis and their altered expression is related to poor prognosis and clinical outcome. These functions strongly suggest their potential use in cancer management as diagnostic or prognostic tools and as new targets of therapeutic intervention.

Human PRDM2: Structure, function and pathophysiology

PRDM2/RIZ is a member of a superfamily of histone/protein methyltransferases (PRDMs), which are characterized by the conserved N-terminal PR domain, with methyltransferase activity and zinc finger arrays at the C-terminus. Similar to other family members, two main protein types, known as RIZ1 and RIZ2, are produced from the PRDM2 locus differing by the presence or absence of the PR domain. The imbalance in their respective amounts may be an important cause of malignancy, with the PR-positive isoform commonly lost or downregulated and the PR-negative isoform always being present at higher levels in cancer cells. Interestingly, the RIZ1 isoform also represents an important target of estradiol action downstream of the interaction with hormone receptor. Furthermore, the imbalance between the two products could also be a molecular basis for other human diseases. Thus, understanding the molecular mechanisms underlying PRDM2 function could be useful in the pathophysiological context, with a potential to exploit this information in clinical practice.

Examining the impact of gene variants on histone lysine methylation

In recent years, there has been a boom in the amount of genome-wide sequencing data that has uncovered important and unappreciated links between certain genes, families of genes and enzymatic processes and diseases such as cancer. Such studies have highlighted the impact that chromatin modifying enzymes could have in cancer and other genetic diseases. In this review, we summarize characterized mutations and single nucleotide polymorphisms (SNPs) in histone lysine methyltransferases (KMTs), histone lysine demethylases (KDMs) and histones. We primarily focus on variants with strong disease correlations and discuss how they could impact histone lysine methylation dynamics and gene regulation.

Upregulated expression of hITF in Crohn's disease and screening of hITF Interactant by a yeast two-hybrid system

AIMS

To study the expression of human intestinal trefoil factor (hITF) mRNA in Crohn's disease and to screen the cellular proteins that can interact with the hITF protein by a yeast two-hybrid system in order to explore the mechanism of hITF in protecting intestinal mucosa from injury.

METHODS

Seventy-eight patients underwent double-balloon enteroscopy (DBE). Expression of hITF mRNA was detected by quantitative real-time polymerase chain reaction analysis (qRT-PCR). The hITF gene was amplified by PCR and cloned into vector pDEST32. The yeast cells cotransformed with pDEST32-hITF and the human jejunal cDNA library were plated in a selective SC-Leu-Trp-His-Ura medium. The subsequent screen was performed with χ-gal detection, and true-positive clones were sequenced and analyzed with bioinformatics. Co-immunoprecipitation (Co-IP) was performed to confirm the binding of putative proteins to the hITF protein.

RESULTS

Thirty-nine patients were diagnosed with Crohn's disease. We found that the expression of hITF mRNA is significantly increased in Crohn's disease compared to normal controls. A total of ten colonies were selected and sequenced. Among these, six colonies were Homo sapiens zinc finger protein 193 (ZNF193), three colonies were Homo sapiens Aldo-keto reductase family 1C 1 (AKR1C1), and one colony was of an unknown gene. A reverse two-hybrid experiment and Co-IP indicated that ZNF193 and AKR1C1 might interact with hITF.

CONCLUSIONS

The expression of hITF mRNA is increased in Crohn's disease. ZNF193 and AKR1C1 are proteins that can interact with the hITF protein by a yeast two-hybrid system and Co-IP, hITF may contribute to the mucosal repair through this interaction.

Cloning, expression, purification and crystallization of the PR domain of human retinoblastoma protein-binding zinc finger protein 1 (RIZ1)

Through alternative promoter usage, human retinoblastoma protein-interacting zinc finger gene RIZ encodes two different protein products, RIZ1 and RIZ2, which have been identified to be a tumor suppressor and a proto-oncoprotein, respectively. Structurally, the two protein products share the same amino acid sequences except that RIZ2 lacks an N-terminal PR domain with methyltransferase activity. Previous studies have shown that over-expression of RIZ2 is usually associated with depressed RIZ1 expression in different human cancers. It is generally believed that RIZ1 and RIZ2 regulate normal cell division and function using a “Yin-Yang” fashion and the PR domain is responsible for the tumor suppressing activity of RIZ1. In order to better understand the biological functions of the PR domain by determining its three-dimensional crystal structure, we expressed, purified and crystallized a construct of the PR domain (amino acid residues 13–190) in this study. The maximum size of the needle-shaped crystals was approximately 0.20 × 0.01 × 0.01 mm.

Epigenetics and cancer

Epigenetic mechanisms act to change the accessibility of chromatin to transcriptional regulation locally and globally via modifications of the DNA and by modification or rearrangement of nucleosomes. Epigenetic gene regulation collaborates with genetic alterations in cancer development. This is evident from every aspect of tumor biology including cell growth and differentiation, cell cycle control, DNA repair, angiogenesis, migration, and evasion of host immunosurveillance. In contrast to genetic cancer causes, the possibility of reversing epigenetic codes may provide new targets for therapeutic intervention.