MicroRNAs are emerging as important regulators of cancer-related processes. The miR-21 microRNA is overexpressed in a wide variety of cancers and has been causally linked to cellular proliferation, apoptosis, and migration. Inhibition of mir-21 in MCF-7 breast cancer cells causes reduced cell growth. Using array expression analysis of MCF-7 cells depleted of miR-21, we have identified mRNA targets of mir-21 and have shown a link between miR-21 and the p53 tumor suppressor protein. We furthermore found that the tumor suppressor protein Programmed Cell Death 4 (PDCD4) is regulated by miR-21 and demonstrated that PDCD4 is a functionally important target for miR-21 in breast cancer cells.

Autophagy is an evolutionarily conserved mechanism of cellular self‐digestion in which proteins and organelles are degraded through delivery to lysosomes. Defects in this process are implicated in numerous human diseases including cancer. To further elucidate regulatory mechanisms of autophagy, we performed a functional screen in search of microRNAs (miRNAs), which regulate the autophagic flux in breast cancer cells. In this study, we identified the tumour suppressive miRNA, miR‐101, as a potent inhibitor of basal, etoposide‐ and rapamycin‐induced autophagy. Through transcriptome profiling, we identified three novel miR‐101 targets, STMN1 , RAB5A and ATG4D . siRNA‐mediated depletion of these genes phenocopied the effect of miR‐101 overexpression, demonstrating their importance in autophagy regulation. Importantly, overexpression of STMN1 could partially rescue cells from miR‐101‐mediated inhibition of autophagy, indicating a functional importance for this target. Finally, we show that miR‐101‐mediated inhibition of autophagy can sensitize breast cancer cells to 4‐hydroxytamoxifen (4‐OHT)‐mediated cell death. Collectively, these data establish a novel link between two highly important and rapidly growing research fields and present a new role for miR‐101 as a key regulator of autophagy. There is a [Have you seen?][1] (November 2011) associated with this Article. [1]: http://dx.doi.org/10.1038/emboj.2011.387

Macroautophagy (hereafter referred to as autophagy) is a tightly regulated intracellular catabolic pathway involving the lysosomal degradation of cytoplasmic organelles and proteins. Central to this process is the formation of the autophagosome, a double membrane–bound vesicle, which is responsible for the delivery of cytoplasmic cargo to the lysosomes. Autophagy levels are constantly changing, allowing adaptation to both immediate and long-term needs of the cell, underlining why tight control of this process is essential in order to prevent the development of pathological disorders. Substantial progress has recently contributed to our understanding of the molecular mechanisms of the autophagy machinery, yet several gaps remain in our knowledge of this process. The discovery of microRNAs (miRNAs) established a new paradigm of post-transcriptional gene regulation and during the past decade these small non-coding RNAs have been closely linked to virtually all known fundamental biological pathways. Deregulation of miRNAs can contribute to the development of human diseases, including cancer, where they can function as bona fide oncogenes or tumor suppressors. In this review, we highlight recent advances linking miRNAs to regulation of the autophagy pathway. This regulation occurs both through specific core pathway components as well as through less well-defined mechanisms. Although this field is still in its infancy, we are beginning to understand the potential implications of these initial findings, both from a pathological perspective, but also from a therapeutic view, where miRNAs can be harnessed experimentally to alter autophagy levels in human tumors, affecting parameters such as tumor survival and treatment sensitivity.

MicroRNAs (miRNAs) have emerged as important gene regulators and are recognized as key players in tumorigenesis. miR-145 is reported to be down-regulated in several cancers, but knowledge of its targets in colon cancer remains limited. To investigate the role of miR-145 in colon cancer, we have employed a microarray based approach to identify miR-145 targets. Based on seed site enrichment analyses and unbiased word analyses, we found a significant enrichment of miRNA binding sites in the 3′-untranslated regions (UTRs) of transcripts down-regulated upon miRNA overexpression. Gene Ontology analysis showed an overrepresentation of genes involved in cell death, cellular growth and proliferation, cell cycle, gene expression and cancer. A number of the identified miRNA targets have previously been implicated in cancer, including YES, FSCN1, ADAM17, BIRC2, VANGL1 as well as the transcription factor STAT1. Both YES and STAT1 were verified as direct miR-145 targets. The study identifies and validates new cancer-relevant direct targets of miR-145 in colon cancer cells and hereby adds important mechanistic understanding of the tumor-suppressive functions of miR-145.

Background: MicroRNAs (miRNAs) are well recognized as gene regulators and have been implicated in the regulation of development as well as human diseases. miR-143 is located at a fragile site on chromosome 5 frequently deleted in cancer, and has been reported to be down-regulated in several cancers including colon cancer.Methods: To gain insight into the role of miR-143 in colon cancer, we used a microarray-based approach in combination with seed site enrichment analysis to identify miR-143 targets.Results: As expected, transcripts down-regulated upon miR-143 overexpression had a significant enrichment of miR-143 seed sites in their 3'UTRs. Here we report the identification of Hexokinase 2 (HK2) as a direct target of miR-143. We show that re-introduction of miR-143 in the colon cancer cell line DLD-1 results in a decreased lactate secretion.Conclusion: We have identified and validated HK2 as a miR-143 target. Furthermore, our results indicate that miR-143 mediated down-regulation of HK2 affects glucose metabolism in colon cancer cells. We hypothesize that loss of miR-143-mediated repression of HK2 can promote glucose metabolism in cancer cells, contributing to the shift towards aerobic glycolysis observed in many tumors.