Question: What is the mechanism of microRNA deregulation in carcinogenesis?

Context:
MicroRNAs are a class of small non-coding RNAs that negatively regulate gene expression by interacting with the 3'UTR of protein-coding mRNA. MicroRNAs are implicated in nearly all major biological and cellular events, and recent findings further link microRNA deregulation to human carcinogenesis.
MiR-657 promotes tumorigenesis in hepatocellular carcinoma by targeting transducin-like enhancer protein 1 through NF-κB pathways.
MicroRNAs (miRNAs), which are small non-coding RNAs, are involved in diverse biological functions and carcinogenesis.
Moreover, we demonstrated that miR-106b downregulates APC expression by directly targeting the 3'-untranslated region of APC messenger RNA.
Furthermore, miRNAs present a mechanism by which genes with diverse functions on multiple pathways can be simultaneously regulated at the post-transcriptional level. However, little is known about the cancer-related pathways through which cancer-associated miRNAs (CA-miRNAs) regulate these processes representing either positive or negative functions in carcinogenesis.
MicroRNAs, known as small noncoding MiRNAs, 19 to 24 nt in length, are important gene regulators and recognized as key players in carcinogenesis. The mechanism lies in that the MiRNAs can conjugate with their targeted mRNA and then lead to the targeted mRNA degradation or repress their translation. Bioinformatic analysis indicates that each MiRNA can regulate hundreds of gene targets and could serve functionally as "oncogenes" or "tumor suppressor genes", and therefore regulate multiple cellular processes relevant to carcinogenesis and cancer progression.
microRNAs (miRs) are endogenous small non-coding RNAs that are aberrantly expressed in various carcinomas.
While deregulated miRNA expression levels have been detected in many tumors, whether miRNA functional impairment is also involved in carcinogenesis remains unknown.
In the last years, microRNAs (miRNA) have emerged as new molecular players involved in carcinogenesis. Deregulation of miRNAs expression has been shown in different human cancer but the molecular mechanism underlying the alteration of miRNA expression is unknown.
These are microRNAs (miRNAs), a class of noncoding RNAs, 20-23 nucleotides in length, that can up or downregulate gene expression of downstream gene targets (including transcription factors, oncogenes, and tumour suppressor genes) at the post-transcriptional level. Some members of this new class of genes seem to have the potential to act simultaneously either as oncogenes or as tumour suppressor genes depending on the molecular microenvironment of the cell.
MicroRNAs can also be affected by chromosomal alterations and thus contribute to carcinogenesis.
Regulation of hepatocarcinogenesis by microRNAs.
MicroRNAs are implicated in nearly all major biological and cellular events, and recent findings further link microRNA deregulation to human carcinogenesis.
miR-106b downregulates adenomatous polyposis coli and promotes cell proliferation in human hepatocellular carcinoma.
However, little is known about the cancer-related pathways through which cancer-associated miRNAs (CA-miRNAs) regulate these processes representing either positive or negative functions in carcinogenesis.
Combined with previous cancer studies, the analysis of the relevance between functions of CA-miRNAs and cancer-related pathways exploring different internal carcinogenesis stimuli also revealed the potential of the top five pathways to regulate core carcinogenesis processes.
MicroRNAs, known as small noncoding MiRNAs, 19 to 24 nt in length, are important gene regulators and recognized as key players in carcinogenesis.
Androgen pathway stimulates microRNA-216a transcription to suppress the tumor suppressor in lung cancer-1 gene in early hepatocarcinogenesis.
Deregulation of microRNAs (miRNAs) is common in advanced human hepatocellular carcinoma (HCC); however, the ones involved in early carcinogenesis have not yet been investigated.
MicroRNA-375 targets AEG-1 in hepatocellular carcinoma and suppresses liver cancer cell growth in vitro and in vivo.
MicroRNAs (miRNAs) are believed to have fundamental roles in tumorigenesis and have great potential for the diagnosis and treatment of cancer. However, the roles of miRNAs in hepatocellular carcinogenesis are still not fully elucidated.
Growing evidence indicates that deregulation of microRNAs (miRNAs) contributes to tumorigenesis.
UNLABELLED: Deregulation of microRNAs (miRNAs) is common in advanced human hepatocellular carcinoma (HCC); however, the ones involved in early carcinogenesis have not yet been investigated.
Deregulation of miRNAs expression has been shown in different human cancer but the molecular mechanism underlying the alteration of miRNA expression is unknown.

Answer: MicroRNAs (miRNAs) are endogenous non-protein coding single-stranded RNAs (19–25 nucleotides in length) generated from  cleavage of larger non-coding RNAs by the ribonuclease III enzyme Dicer. They become part of the RNA-induced silencing complex and negatively regulate gene expression by binding to homologous 3'-UTR region of target protein-coding mRNAs as an imperfect match, causing translational repression or degradation. Approximately one-third of the protein-coding genes are susceptible to miRNA regulation. Accumulating evidence indicates that deregulated miRNA expression is associated with the onset and progression of a number of human cancers. Therefore, cancer-associated miRNAs (CA-miRNAs) could regulate target genes by acting either as "oncogenes" or "tumor suppressor miRNA (TS-miRNAs)". In line with this, numerous cancers (e.g. breast, lung, oesophageal, prostate, pancreatic, gastric and colon cancer) have been classified based on their unique miRNA expression profile.