The noncoding RNA, miR‐126, suppresses the growth of neoplastic cells by targeting phosphatidylinositol 3‐kinase signaling and is frequently lost in colon cancers

Abstract

MicroRNAs (miRNA/miR) are a class of small non-coding RNAs implicated in the pathogenesis of various malignancies. In the current study, using micro(RNA)arrays, we found a ubiquitous loss of miR-126 expression in colon cancer lines when compared to normal human colon epithelia. Reconstitution of miR-126 in colon cancer cells resulted in a significant growth reduction as evidenced in clonogenic assays. A search for miR-126 gene targets revealed p85β, a regulatory subunit involved in stabilizing and propagating the PI3K signal, as one of the potential substrates. Restoration of miR-126 in cancer cells induced a ≥3-fold reduction in p85β protein levels, with no concomitant change in p85α, a gene that is functionally related to p85β but not a supposed target of miR-126. Additionally, using reporter constructs, we show that the p85β-3′ UTR is directly targeted by miR-126. Furthermore, this miR-126 mediated reduction of p85β was accompanied by a substantial reduction in phosphorylated AKT levels in the cancer cells, suggesting an impairment in PI3K signaling. Finally, in a panel of matched normal colon and primary colon tumors, each of the tumors demonstrated miR-126 down-regulation together with an increase in the p85β protein level. Taken together, we propose that miR-126 regulates PI3K signaling partly by targeting p85β, and that the loss of miR-126 may provide a selective growth advantage during colon carcinogenesis.

Attenuation of the beta-catenin/TCF4 complex in colorectal cancer cells induces several growth-suppressive microRNAs that target cancer promoting genes

“…Efficient transfection was confirmed by qPCR ( Figure 3a). As expected, miR-126 and miR-145 reduced cell viability (Guo et al, 2008;Schepeler et al, 2008), and interestingly miR-139-5p and miR-30e-3p also inhibited cell viability in a dosage-dependent manner ( Figure 3b). Restriction of cell growth was also evident in a detailed time course experiment (Figure 3c).…”

“…dnTCF4-responsive miRNAs are downregulated in CRC specimens and CRC cell lines Among the numerous miRNAs altered as a consequence of dnTCF4 overexpression, we noticed several of the upregulated miRNAs to have been previously associated with restriction of cancer cell growth (miR449a, (Henson et al, 2009;Noonan et al, 2009;Slaby et al, 2009;Chen et al, 2010;Ding et al, 2010;Ostenfeld et al, 2010). Interestingly, in addition to prominent growth-inhibitory miRNAs commonly downregulated in CRC, such as miR-126 and miR-145 (Guo et al, 2008;Schepeler et al, 2008), several miRNAs with unknown function in CRC cells (for example, miR-574-3p, miR-30e-3p and miR-139-5p) were also upregulated, which prompted us to hypothesize that some of these miRNAs may also be dysregulated in CRC. Accordingly, we examined miRNA expression using the same miRNA TaqMan platform in 46 primary stage II CRCs and 14 adjacent normal mucosa samples.…”

“…Consequently, our results imply that PI3K isoforms do not act redundantly, and CRC cells remain sensitive to repressive signals acting on PIK3C2A, in this case illustrated by miR-30e-3p. Although this is, to our knowledge, the first example of PI3K isoform levels modulated directly by miRNAs, other examples of miRNAs acting indirectly on PI3K signaling exist as seen for several miRNAs targeting the PI3K antagonist PTEN (Kato et al, 2009;Small et al, 2010), and miR-126 targeting the PI3K subunit p85beta (Guo et al, 2008). In summary, our results point to the notion that blockage of constitutive Wnt signaling in CRC cells lead to upregulation of several growth-suppressive miRNAs, thus paralleling the functional response observed at the mRNA level where numerous negative growth regulators (for example, FOXO3A, DAPK2, HATH1 and CDKN1A/p21) are known to be induced under similar conditions in CRC cells (van de Wetering et al, 2002;Tsuchiya et al, 2007;Dehner et al, 2008;Li et al, 2009).…”

Macro-management of microRNAs in cell cycle progression of tumor cells and its implications in anti-cancer therapy

“…Many members of the PI3K/AKT pathway are regulated by miRNAs. miR-29a and miR-126 target the p85α and p85β subunits of PI3K [74,75] , respectively. The down-regulation of miR-126 in colon cancer is associated with the up-regulation of the p85β subunit, which induces the phosphorylation of AKT and promotes the proliferation of colon cancer cells [75] .…”

Next-generation biobanking of metastases to enable multidimensional molecular profiling in personalized medicine

“…As shown in Figure 5c, we were able to ascertain upregulation of genes typically found to be activated in colon adenocarcinoma, including JUN, PIK3R2 and MYC that are, respectively, in the top 27, 20 and 7% most abundant genes detected on the array. 39,40 The gene expression data correlated well with hypomethylation of the proto-oncogenes (JUN, MYC) or promoter region in the case of PIK3R2. The concordance of results from the different platforms supports the compatibility of our next-generation biobanking protocol.…”