A role for low-abundance miRNAs in colon cancer: the miR-206/Krüppel-like factor 4 (KLF4) axis

Abstract

BackgroundMicroRNAs (miRNAs or miRs) are short non-coding RNAs that affect the expression of genes involved in normal physiology, but that also become dysregulated in cancer development. In the latter context, studies to date have focused on high-abundance miRNAs and their targets. We hypothesized that among the pool of low-abundance miRNAs are some with the potential to impact crucial oncogenic signaling networks in colon cancer.ResultsUnbiased screening of over 650 miRNAs identified miR-206, a low-abundance miRNA, as the most significantly altered miRNA in carcinogen-induced rat colon tumors. Computational modeling highlighted the stem-cell marker Krüppel-like factor 4 (KLF4) as a potential target of miR-206. In a panel of primary human colon cancers, target validation at the mRNA and protein level confirmed a significant inverse relationship between miR-206 and KLF4, which was further supported by miR-206 knockdown and ectopic upregulation in human colon cancer cells. Forced expression of miR-206 resulted in significantly increased cell proliferation kinetics, as revealed by real-time monitoring using HCT116 cells.ConclusionsEvolutionarily conserved high-abundance miRNAs are becoming established as key players in the etiology of human cancers. However, low-abundance miRNAs, such as miR-206, are often among the most significantly upregulated miRNAs relative to their expression in normal non-transformed tissues. Low-abundance miRNAs are worthy of further investigation, because their targets include KLF4 and other pluripotency and cancer stem-cell factors.

The role of microRNA in nutritional control

“…Food components can either promote or repress carcinogenesis and some of these effects involve miRNAs [3].For example, colon cancer can be experimentally induced with known mutagenic heterocyclic amines that are generated during the cooking of meat and fish [e.g. 2-amino-1-methyl-6-phenyl-imidazo [4,5-b]pyridine (PhIP)] and miR-206 is highly upregulated in this process [41]. The let-7/c-Myc/Lin28 axis is also dysregulated in PhIPinduced rat colon carcinogenesis, and feeding spinach to exposed animals not only inhibited tumour formation but also partially normalized this pathway [42].…”

Roles of the canonical myomiRs miR-1, -133 and -206 in cell development and disease

“…Importantly, key targets of miR12 and 206 include enzymes of the pentose phosphate pathway (including G6PD, PGD and TKT) and the tricarboxylic acid cycle enzyme GPD2, which increase their activities and potentiate cancer cell proliferation and compromise patient survival. Pleiotropic factors, such as KLF4, HDAC4 and IGFR1 are also elevated in gastric carcinoma and in breast cancer cells in part due to the loss of miR206 [108] , yet in contrast KLF4 is reduced in colon cancer tissue due to strong upregulation of 206 [116] . KLF4 is a zinc-finger transcription factor that binds to the TGFβ1 promoter and is important during normal cellular differentiation and proliferation.…”

“…Many of the reports identify reduction in a single myomiR, but in case studies of particular cancers often the different myomiRs have been identified as downregulated, for example in NSCLC tumor samples, miR1 [100] , 133a [85,115] , 133b [85,115] , 206 [107] or miR1/206 [99] have been reported, by implication dysregulation of all of the myomiRs. Si milarly, for colorectal cancer, downregulated miR1 [101] , 133a [104] , or 133b [86] , or upregulated miR206 [116] , while in prostate cancer downregulated miR1 [101,102] and miR206 [102] , miR133a [97,102] and miR133b [95,96] have been variously reported (Table 3). Either these studies have examined different subclasses of the particular cancer which have different myomiR profiles, or more likely the method of miR detection or the purpose of the study (e.g., relating a particular miR to a particular deregulated target gene) may have influenced the findings reported, leading to some potentially conflicting and inconsistent reports.…”

Divergent roles of p120‐catenin isoforms linked to altered cell viability, proliferation, and invasiveness in carcinogen‐induced rat skin tumors

“…Effects of p120‐catenin isoforms were examined on (B) cell viability; at the 96 h time‐point, p120‐catenin isoforms 1A, 3A, and 4A were significantly different from the vector control ( P < 0.05). (C) Bromodeoxyuridine (BrdU) incorporation, mean ± SD, n = 3; insert shows BrdU‐positive cells, white arrows; (D) cell invasion assays, using real‐time monitoring as reported by Parasramka et al; representative findings from at least three replicate experiments, each giving similar outcomes. The slope of the line for p120‐catenin isoform 1A was significantly different from the other slopes shown, including the vector control, P < 0.05…”