The microRNA miR-34a is a tumor suppressor transcript, and its loss has been prominently linked to various human cancers, including malignancies of the brain.
Conversely, upregulation of miR-34a by p53 is thought to enhance its acetylation and activity and contribute to the pro-apoptotic effects of this tumor suppressor.
MiR-34a acts as tumor suppressor microRNA (miRNA) in several cancers, including multiple myeloma (MM), by controlling the expression of target proteins involved in cell cycle, differentiation and apoptosis.
Many miRNAs play crucial roles in the regulation of cancer, for instance, miR‑34a functions as a tumor suppressor, and is often downregulated during cancer.
Although aberrant expression of miR-34a, an essential tumor suppressor miRNA, has been frequently observed in colon cancer (CCa), whether miR-34a can regulate CCa progression by modulating other facets of this malignancy (such as multidrug resistance, MDR) remains unknown.
No significant difference was observed in AIP mRNA expression between tumors with low or high AIP protein expression suggesting post-transcriptional regulation. miR-34a was highly expressed in low AIP protein samples compared high AIP protein adenomas and miR-34a levels were inversely correlated with response to SSA therapy. miR-34a inhibited the luciferase-AIP-3'UTR construct, suggesting that miR-34a binds to AIP-3'UTR.
Moreover, miR-34a administration significantly delayed tumor growth of subcutaneously and orthotopically implanted tumors in nude mice, and was accompanied by c-SRC downregulation.
For this purpose, we used stem-loop reverse transcription-polymerase chain reaction to analyze the expression of the miR-34 family in paired tumor and normal tissue from 70 surgically resected NSCLC patients who received no postsurgical treatment until relapse.
Transfection of miR-34a into PC-3 cells also significantly inhibited in vivo xenograft tumor growth in nude mice. miR-34a downregulated expression of c-Myc oncogene by targeting its 3' UTR as shown by luciferase reporter assays. miR-34a was found to repress RhoA, a regulator of cell migration and invasion, by suppressing c-Myc-Skp2-Miz1 transcriptional complex that activates RhoA.
Moreover, miR‑34 has been identified as a tumour‑suppressor in GC. p53‑induced miR‑34 regulates several different target genes and signalling pathways, inducing apoptosis, senescence, and cell cycle arrest and repressing GC cell proliferation, migration and metastasis, thus contributing to the suppression of carcinogenesis and GC cancer progression.
The oncogene role of SNHG7 in vivo was also confirmed and found that knockdown of SNHG7 delayed the tumor growth with increased miR-34a level and Ki-67 level in OS tissues.
MicroRNA miR-34 was recently found to be a direct target of p53, functioning downstream of the p53 pathway as a tumor suppressor. miR-34 targets Notch, HMGA2, and Bcl-2, genes involved in the self-renewal and survival of cancer stem cells.
Importantly, the targeting of miRNAs (like use of anti-miR-155 or miR-34a mimic) could provide a novel therapeutic approach as evidenced by tumour regression in xenograft mouse models and initial promising data from clinical trials.
Knocking down of sONE resulted in a marked decrease in TP53 and increase in c-Myc and consequently altering the expression status of their downstream tumor suppressor microRNAs (miRNAs) such as miR-34a, miR-15, miR-16, and let-7a.
MiR-34a is an important tumor suppressor whose expression is suppressed in cancer stem cells (CSCs), and re-expression of miR-34a is able to inhibit the tumorigenic activity of CSCs.
In this study, expression of miR-34a, let-7a and apoptosis pathway genes such as Bcl-2, Caspase-3 and P53 were evaluated using quantitative real-time PCR in 45 paired samples of normal margin and tumor tissue collected from breast cancer patient at advanced stage (3-4).
Taken together, our results elucidated the intricate cross-talk between p53 and miR-34 miRNAs and revealed an important tumor suppressor effect generated by this positive feedback loop.