Luigia Meo

The urokinase-receptor (uPAR) exerts multiple functions supporting most cancer hallmarks. Increased uPAR expression is associated with an unfavorable prognosis in several cancer types, including hematologic malignancies. We previously reported that three oncosuppressor microRNAs (miRNAs) can target the 3′untranslated region (3′UTR) of the uPAR mRNA and that uPAR mRNA is a competitive endogenous RNA (ceRNA) able to recruit oncosuppressor miRs, thus impairing their activity. We now show that uPAR mRNA can also be targeted by oncosuppressor members of the let-7 miRNA family in acute myeloid leukemia (AML) cell lines. Indeed, let-7a, let7d and let-7g directly target the 3′UTR of uPAR mRNA, thus down-regulating uPAR expression. These let-7 miRNAs are expressed in KG1 and U937 AML cells; their levels are high in KG1 cells, which express low uPAR levels, and low in the U937 cell line, expressing high levels of uPAR. Overexpression of these miRNAs down-regulates uPAR expression and impairs the adhesion to fibronectin and migration of U937 cells, without affecting their proliferation. Accordingly, the overexpression of specific inhibitors targeting these let-7 miRNAs efficiently increases uPAR expression in KG1 cells. These results indicate that selected let-7 miRNAs regulate uPAR expression and impair the adhesion and migration of AML cells.

Most commonly diagnosed cancer pathologies in the pediatric population comprise leukemias and cancers of the nervous system. The percentage of cancer survivors increased from approximatively 50% to 80% thanks to improvements in medical treatments and the introduction of new chemotherapies. However, as a consequence, heart disease has become the main cause of death in the children due to the cardiotoxicity induced by chemotherapy treatments. The use of different cardiovascular biomarkers, complementing data obtained from electrocardiogram, echocardiography cardiac imaging, and evaluation of clinical symptoms, is considered a routine in clinical diagnosis, prognosis, risk stratification, and differential diagnosis. Cardiac troponin and natriuretic peptides are the best-validated biomarkers broadly accepted in clinical practice for the diagnosis of acute coronary syndrome and heart failure, although many other biomarkers are used and several potential markers are currently under study and possibly will play a more prominent role in the future. Several studies have shown how the measurement of cardiac troponin (cTn) can be used for the early detection of heart damage in oncological patients treated with potentially cardiotoxic chemotherapeutic drugs. The advent of high sensitive methods (hs-cTnI or hs-cTnT) further improved the effectiveness of risk stratification and monitoring during treatment cycles.

Various species of non-coding RNAs (ncRNAs) may act as functional molecules regulating diverse biological processes. In cancer cell biology, ncRNAs include RNAs that regulate the expression of oncogenes and tumor suppressor genes through various mechanisms. The urokinase (uPA)-mediated plasminogen activation system (PAS) includes uPA, its inhibitors PAI-1 and PAI-2 and its specific cellular receptor uPAR; their increased expression represents a negative prognostic factor in several cancers. Here, we will briefly describe the main uPA-mediated PAS components and ncRNA species; then, we will review more recent evidence of the roles that ncRNAs may play in regulating the expression and functions of uPA-mediated PAS components in cancer.

The 3′untranslated region (3′UTR) of the urokinase (uPA) receptor (uPAR) mRNA can act as a competitive endogenous RNA (ceRNA) in acute myeloid leukaemia (AML) cells, promoting the expression of pro-tumoral targets, including uPAR. Here, we identified three variants of uPAR mRNA containing the 3′UTR, in KG1 and U937 leukaemia cells expressing low and high uPAR levels, respectively. Identified variants lack exon 5 (uPAR Δ5) or exon 6 (uPAR Δ6) or part of exon 6, exon 7 and part of 3′UTR (uPAR Δ6/7). uPAR Δ5 and uPAR Δ6 transcript levels were higher in U937 cells compared to KG1 cells. Both uPAR variants were expressed also in AML blasts, at higher levels as compared to CD34 hematopoietic cells from healthy donors. The presence of the 3′UTR conferred high instability to the uPAR Δ5 variant transcript, preventing its translation in protein. Overexpression of the uPAR Δ5-3′UTR variant regulated the expression of some pro-tumoral factors previously reported to be regulated by the 3′UTR of uPAR and increased KG1 cell adhesion, migration and proliferation. These results demonstrate the expression of uPAR mRNA variants containing the 3′UTR in AML cells and the ceRNA activity and the biological effects of the uPAR Δ5-3′UTR variant.