ABSTRACT
Notch signalling is critical for the development of the nervous system. In the zebrafish mindbomb mutants, disruption of E3 ubiquitin ligase activity inhibits Notch signalling. In these mutant embryos, precocious development of primary neurons leading to depletion of neural progenitor cells results in a neurogenic phenotype characterized by defects in neural patterning and brain development. Cyclin-dependent kinase 5 (Cdk5), a predominant neuronal kinase, is involved in a variety of essential functions of the nervous system. Most recently, mammalian studies on Notch and Cdk5 regulating each other's function have been emerging. The status of Cdk5 in the mindbomb mutant embryos with excessive primary neurons is not known. In situ hybridization of the zebrafish mindbomb mutant embryos uncovered a robust upregulation in Cdk5 expression but with a reduced Cdk5 activity. The implications of these findings in both the mammalian system and zebrafish are discussed in this mini-review to provide a glimpse into the relationship between Notch and Cdk5 that may explain certain neurodevelopmental defects associated with either mutations in ubiquitin ligase or altered expression of Cdk5.
Subject(s)
Cyclin-Dependent Kinase 5/metabolism , Mutation/genetics , Receptors, Notch/metabolism , Zebrafish Proteins/genetics , Zebrafish/metabolism , Animals , Models, Biological , Up-Regulation/geneticsABSTRACT
MicroRNA-101, a tumor suppressor microRNA (miR), is often downregulated in cancer and is known to target multiple oncogenes. Some of the genes that are negatively regulated by miR-101 expression include histone methyltransferase EZH2 (enhancer of zeste homolog 2), COX2 (cyclooxygenase-2), POMP (proteasome maturation protein), CERS6, STMN1, MCL-1 and ROCK2, among others. In the present study, we show that miR-101 targets transcriptional coactivator SUB1 homolog (Saccharomyces cerevisiae)/PC4 (positive cofactor 4) and regulates its expression. SUB1 is known to have diverse role in vital cell processes such as DNA replication, repair and heterochromatinization. SUB1 is known to modulate transcription and acts as a mediator between the upstream activators and general transcription machinery. Expression profiling in several cancers revealed SUB1 overexpression, suggesting a potential role in tumorigenesis. However, detailed regulation and function of SUB1 has not been elucidated. In this study, we show elevated expression of SUB1 in aggressive prostate cancer. Knockdown of SUB1 in prostate cancer cells resulted in reduced cell proliferation, invasion and migration in vitro, and tumor growth and metastasis in vivo. Gene expression analyses coupled with chromatin immunoprecipitation revealed that SUB1 binds to the promoter regions of several oncogenes such as PLK1 (Polo-like kinase 1), C-MYC, serine-threonine kinase BUB1B and regulates their expression. Additionally, we observed SUB1 downregulated CDKN1B expression. PLK1 knockdown or use of PLK1 inhibitor can mitigate oncogenic function of SUB1 in benign prostate cancer cells. Thus, our study suggests that miR-101 loss results in increased SUB1 expression and subsequent activation of known oncogenes driving prostate cancer progression and metastasis. This study therefore demonstrates functional role of SUB1 in prostate cancer, and identifies its regulation and potential downstream therapeutic targets of SUB1 in prostate cancer.
Subject(s)
DNA-Binding Proteins/genetics , MicroRNAs/genetics , Prostatic Neoplasms/genetics , Transcription Factors/genetics , Animals , Cell Proliferation/genetics , DNA-Binding Proteins/biosynthesis , Gene Expression Regulation, Neoplastic , Gene Knockdown Techniques , Heterografts , Humans , Male , Mice , MicroRNAs/biosynthesis , Prostatic Neoplasms/metabolism , Prostatic Neoplasms/pathology , Transcription Factors/biosynthesisABSTRACT
The process of epithelial-mesenchymal transition (EMT), in addition to being an initiating event for tumor metastasis, is implicated in conferring several clinically relevant properties to disseminating cancer cells. These include stem cell-like properties, resistance to targeted therapies and ability to evade immune surveillance. Enrichment analysis of gene expression changes during transforming growth factor-ß (TGF-ß)-induced EMT in lung cancer cells identified complement cascade as one of the significantly enriched pathway. Further analysis of the genes in the complement pathway revealed an increase in the expression of complement inhibitors and a decrease in the expression of proteins essential for complement activity. In this study, we tested whether EMT confers resistance to complement-dependent cytotoxicity (CDC) in lung cancer cells and promotes tumor progression. CD59 is a potent inhibitor of membrane attack complex that mediates complement-dependent cell lysis. We observed a significant increase in the CD59 expression on the surface of cells after TGF-ß-induced EMT. Furthermore, CD59 knockdown restored susceptibility of cells undergoing EMT to cetuximab-mediated CDC. TGF-ß-induced CD59 expression during EMT is dependent on Smad3 but not on Smad2. Chromatin immunoprecipitation analysis confirmed that Smad3 directly binds to the CD59 promoter. Stable knockdown of CD59 in A549 cells inhibited experimental metastasis. These results demonstrate that TGF-ß-induced EMT and CD59 expression confers an immune-evasive mechanism to disseminating tumor cells facilitating tumor progression. Together, our data demonstrates that CD59 inhibition may serve as an adjuvant to enhance the efficacy of antibody-mediated therapies, as well as to inhibit metastasis in lung cancer.
