Haiqi Lu

MicroRNAs as Potential Biomarkers in Cancer: Opportunities and Challenges

MicroRNAs (miRNAs) are a group of small noncoding RNAs (ncRNAs) that posttranscriptionally regulate gene expression by targeting their corresponding messenger RNAs (mRNAs). Dysregulated miRNAs have been considered as a new type of ‘‘oncomiRs” or ‘‘tumor suppressors,” playing essential roles in cancer initiation and progression. Using genome-wide detection methods, ubiquitously aberrant expression profiles of miRNAs have been identified in a broad array of human cancers, showing great potential as novel diagnostic and prognostic biomarkers of cancer with high specificity and sensitivity. The detectable miRNAs in tissue, blood, and other body fluids with high stability provide an abundant source for miRNA-based biomarkers in human cancers. Despite the fact that an increasing number of potential miRNA biomarkers have been reported, the transition of miRNAs-based biomarkers from bench to bedside still necessitates addressing several challenges. In this review, we will summarize our current understanding of miRNAs as potential biomarkers in human cancers.

MicroRNAs in Hepatocellular Carcinoma: Regulation, Function, and Clinical Implications

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide and the third cause of cancer-related death. Poor understanding of the mechanisms underlying the pathogenesis of HCC makes it difficult to be diagnosed and treated at early stage. MicroRNAs (miRNAs), a class of noncoding single-stranded RNAs of ~22 nucleotides in length, posttranscriptionally regulate gene expression by base pairing with the 3′ untranslated regions (3′UTRs) of target messenger RNAs (mRNAs). Aberrant expression of miRNAs is found in many if not all cancers, and many deregulated miRNAs have been proved to play crucial roles in the initiation and progression of cancers by regulating the expression of various oncogenes or tumor suppressor genes. In this Paper, we will summarize the regulations and functions of miRNAs aberrantly expressed in HCC and discuss the potential application of miRNAs as diagnostic and prognostic biomarkers of HCC and their potential roles in the intervention of HCC.

Regulation and function of mitophagy in development and cancer.

Beyond its role in recycling intracellular components nonselectively to sustain survival in response to metabolic stresses, autophagy can also selectively degrade specific cargoes such as damaged or dysfunctional organelles to maintain cellular homeostasis. Mitochondria, known as the power plant of cells, are the critical and dynamic organelles playing a fundamental role in cellular metabolism. Mitophagy, the selective autophagic elimination of mitochondria, has been identified both in yeast and in mammalian cells. Moreover, defects in mitophagy may contribute to a variety of human disorders such as neurodegeneration and myopathies. However, the role of mitophagy in development and cancer remains largely unclear. In this review, we summarize our current knowledge of the regulation and function of mitophagy in development and cancer.

Yin Yang-1 suppresses differentiation of hepatocellular carcinoma cells through the downregulation of CCAAT/enhancer-binding protein alpha

As a member of the GLI-Kruppel family of transcriptional factors, Yin Yang-1 (YY1) functions as an oncogene in various types of cancers. However, the role of YY1 in hepatocellular carcinogenesis remains unknown. In this report, we investigated the relevance of YY1 to hepatocellular carcinoma (HCC) development. We found that YY1 was upregulated in HCC cell lines. Ectopic YY1 expression promoted the growth of non-tumor liver cells that expressed low level of YY1. In contrast, YY1 depletion inhibited the growth of HCC cells which was accompanied with distinct morphological changes. Moreover, the phenotypic changes induced by YY1 depletion were attributed to cellular differentiation rather than cellular senescence. CCAAT/enhancer-binding protein alpha (CEBPA) which was important to regulate differentiation of hepatocytes was found as the direct target downregulated by YY1. Restoration of CEBPA in YY1-expressing HCC cells induced cellular differentiation and growth inhibition while knockdown of CEBPA expression in non-tumor liver cells promoted cell growth. In summary, our study demonstrated that YY1 could promote hepatocellular carcinogenesis and inhibit cellular differentiation through the downregulation of CEBPA expression.

YY1-MIR372-SQSTM1 regulatory axis in autophagy

Autophagy is a self-proteolytic process that degrades intracellular material to enable cellular survival under unfavorable conditions. However, how autophagy is activated in human carcinogenesis remains largely unknown. Herein we report an epigenetic regulation of autophagy in human cancer cells. YY1 (YY1 transcription factor) is a well-known epigenetic regulator and is upregulated in many cancers. We found that YY1 knockdown inhibited cell viability and autophagy flux through downregulating SQSTM1 (sequestosome 1). YY1 regulated SQSTM1 expression through the epigenetic modulation of the transcription of MIR372 (microRNA 372) which was found to target SQSTM1 directly. During nutrient starvation, YY1 was stimulated to promote SQSTM1 expression and subsequent autophagy activation by suppressing MIR372 expression. Similar to YY1 depletion, MIR372 overexpression blocked autophagy activation and inhibited in vivo tumor growth. SQSTM1 upregulation and competent autophagy flux thus contributed to the oncogenic function of YY1. YY1-promoted SQSTM1 upregulation might be a useful histological marker for cancer detection and a potential target for drug development.

Histone deacetylase 3 inhibits expression of PUMA in gastric cancer cells

During cancer development, tumor suppressor genes were silenced by promoter methylation or histone deacetylation. Histone deacetylases (HDACs) are important to maintain histone deacetylation. HDAC inhibitors (HDACis) were thus proposed as a new therapeutic approach to cancer. The current study aims to understand the effect and molecular mechanisms of HDACis on gastric cancer cells. Trichostatin A (TSA) significantly inhibited the growth of gastric cancer cells by inducing apoptosis. Gene profiling results showed PUMA (p53 upregulated modulator of apoptosis) as one of 122 genes upregulated in TSA-treated gastric cancer cells. PUMA was downregulated in gastric cancer cell lines and primary gastric carcinoma tissues. Patients with low PUMA expression had significant decreases in overall survival (HR, 2.04; p = 0.047). Ectopic PUMA expression inhibited the growth of gastric cancer cells while PUMA depletion promoted cellular growth. The knockdown of HDAC3 but not other HDACs upregulated PUMA expression. HDAC3 could bind to PUMA promoter, which was abrogated after TSA treatment. In contrast to TSA and SB, HDAC3 siRNA failed to upregulate p53 expression but promoted the interaction of p53 with PUMA promoter. In summary, proapoptotic PUMA was downregulated in gastric cancer and its mRNA expression level is a valuable prognosis factor for gastric cancer. HDAC3 is important to downregulate PUMA expression in gastric cancer and HDACis, like TSA, promoted PUMA expression through stabilizing p53 in addition to HDAC3 inhibition. In combination with chemotherapy, targeting HDAC3 might be a promising strategy to induce apoptosis of gastric cancer cells.

Downregulation of histone deacetylase 1 by microRNA‐520h contributes to the chemotherapeutic effect of doxorubicin

Doxorubicin induces DNA damage to exert its anti‐cancer function. Histone deacetylase 1 (HDAC1) can protect the genome from DNA damage. We found that doxorubicin specifically downregulates HDAC1 protein expression and identified HDAC1 as a target of miR‐520h, which was upregulated by doxorubicin. Doxorubicin‐induced cell death was impaired by exogenous HDAC1 or by miR‐520h inhibitor. Moreover, HDAC1 reduced the level of γH2AX by preventing the interaction of doxorubicin with DNA. In summary, doxorubicin downregulates HDAC1 protein expression, by inducing the expression of HDAC1‐targeting miR‐520h, to exacerbate DNA–doxorubicin interaction. The upregulation of HDAC1 protein may contribute to drug resistance of human cancer cells and targeting HDAC1 is a promising strategy to increase the clinical efficacy of DNA damage‐inducing chemotherapeutic drugs.

New tumor suppressor CXXC finger protein 4 inactivates mitogen activated protein kinase signaling

As a well‐characterized master player in epigenetic regulatory network, EZH2 is widely implicated in the development of many malignancies. We previously found that EZH2 promoted Wnt/β‐catenin activation through downregulation of CXXC4 expression. In this report, we demonstrated that CXXC4 inhibited MAPK signaling through binding to ERK‐1/2 and abrogating the interaction of ERK 1/2 with MEK1/2. L183, the critical residue in CXXC4 ERK D domain, was found to be essential for CXXC4–ERK 1/2 interaction and the growth inhibitory effect of CXXC4 in human cancer cells. In summary, CXXC4 directly disrupted MEK1/2–ERK 1/2 interaction to inactivate MAPK signaling. L183 site is indispensable for the binding of CXXC4 to ERK1/2 and growth inhibitory effect of CXXC4. Therefore, EZH2 can activate MAPK signaling by inhibiting CXXC4 expression.

Hepatic Tmem30a Deficiency Causes Intrahepatic Cholestasis by Impairing Expression and Localization of Bile Salt Transporters

Mutations in ATP8B1 or ATP11C (members of P4-type ATPases) cause progressive familial intrahepatic cholestasis type 1 in human or intrahepatic cholestasis in mice. Transmembrane protein 30A (TMEM30A), a β-subunit, is essential for the function of ATP8B1 and ATP11C. However, its role in the etiology of cholestasis remains poorly understood. To investigate the function of TMEM30A in bile salt (BS) homeostasis, we developed Tmem30a liver-specific knockout (LKO) mice. Tmem30a LKO mice experienced hyperbilirubinemia, hypercholanemia, inflammatory infiltration, ductular proliferation, and liver fibrosis. The expression and membrane localization of ATP8B1 and ATP11C were significantly reduced in Tmem30a LKO mice, which correlated with the impaired expression and localization of BS transporters, such as OATP1A4, OATP1B2, NTCP, BSEP, and MRP2. The proteasome inhibitor bortezomib partially restored total protein levels of BS transporters but not the localization of BS transporters in the membrane. Furthermore, the expression of nuclear receptors, including FXRα, RXRα, HNF4α, LRH-1, and SHP, was also down-regulated. A cholic acid-supplemented diet exacerbated the liver damage in Tmem30a LKO mice. TMEM30A deficiency led to intrahepatic cholestasis in mice by impairing the expression and localization of BS transporters and the expression of related nuclear receptors. Therefore, TMEM30A may be a novel genetic determinant of intrahepatic cholestasis.

CXXC4 activates apoptosis through up-regulating GDF15 in gastric cancer

Worldwide, gastric cancer is one of the most fatal cancers. Epigenetic alterations in gastric cancer play important roles in silencing of tumor suppressor genes. We previously found that CXXC finger protein 4 (CXXC4) was a novel tumor suppressor in gastric cancer. In this report, we demonstrated that CXXC4 inhibited growth of gastric cancer cells as a pro-apoptotic factor. This inhibition could be reversed by the pan-caspase inhibitor called Z-VAD-FMK. However, CXXC4 with mutations in its DNA binding domain failed to induce apoptosis. Growth differentiation factor 15 (GDF15) was identified as one of potential targets responsible for CXXC4-induced apoptosis. CXXC4 activated GDF15 transcription through enhancing the interaction of transcription factor Sp1 with GDF15 promoter. In summary, the nuclear protein CXXC4 activated apoptosis in gastric cancer through up-regulating its novel potential downstream target GDF15. GDF15 might be a promising target for clinical treatment of gastric cancer with CXXC4 deficiency.