Due to accumulation of many genetic changes in cancer oncogenes and tumor suppressor genes can generate an immune response by presenting antigenic peptides on the cell surface. On the other hand, in many cases immune response is muted and unable to effectively fight tumors. Recent studies have shown that T-cell responses are dependent on cytotoxic T cells, these responses can be inhibited by the interaction receptors on the surface of immune cells such as PD-1 with the molecules expressed in the surface of tumors, such as PD-L1. Thus, immune therapies were developed to block this interaction thereby triggering the cytotoxic activity of these activated T cells. In this short article we summarize the role of microRNAs, in particularly miR-155 in avoidance of immune mediated tumor rejection by malignant cells.

Dysregulated apoptosis and proliferation are fundamental properties of cancer, and microRNAs (miRNA) are critical regulators of these processes. Loss of miR- 15a/16- 1 at chromosome 13q14 is the most common genomic aberration in chronic lympho-cytic leukemia (CLL). Correspondingly, the deletion of either murine miR- 15a/16- 1 or miR- 15b/16- 2 locus in mice is linked to B cell lymphoproliferative malignancies. However, unexpectedly, when both miR-15/16 clusters are eliminated, most double knockout (DKO) mice develop acute myeloid leukemia (AML). Moreover, in patients with CLL, significantly reduced expression of miR-15a, miR-15b, and miR-16 associates with progression of myelodysplastic syndrome to AML, as well as blast crisis in chronic myeloid leukemia. Thus, the miR-15/16 clusters have a biological relevance for myeloid neoplasms. Here, we demonstrate that the myeloproliferative phenotype in DKO mice correlates with an increase of hematopoietic stem and progenitor cells (HSPC) early in life. Using single -cell transcriptomic analyses, we presented the molecular underpinning of increased myeloid output in the HSPC of DKO mice with gene signatures suggestive of dysregulated hematopoiesis, metabolic activities, and cell cycle stages. Functionally, we found that multipotent progenitors (MPP) of DKO mice have increased self- renewing capacities and give rise to significantly more progeny in the granulocytic compartment. Moreover, a unique transcriptomic signature of DKO MPP correlates with poor out-come in patients with AML. Together, these data point to a unique regulatory role for miR-15/16 during the early stages of hematopoiesis and to a potentially useful biomarker for the pathogenesis of myeloid neoplasms.

Chronic lymphocytic leukemia (CLL) is one of the most diagnosed forms of leukemia worldwide and it is usually classified into two forms: indolent and aggressive. These two forms are characterized by distinct molecular features that drive different responses to treatment and clinical outcomes. In this context, a better understanding of the molecular landscape of the CLL forms may potentially lead to the development of new drugs or the identification of novel biomarkers. Human endogenous retroviruses (HERVs) are a class of transposable elements that have been associated with the development of different human cancers, including different forms of leukemias. However, no studies about HERVs in CLL have ever been reported so far. Here, we present the first locus-specific profiling of HERV expression in both the aggressive and indolent forms of CLL. Our analyses revealed several dysregulations in HERV expression occurring in CLL and some of them were specific for either the aggressive or indolent form of CLL. Such results were also validated by analyzing an external cohort of CLL patients and by RT-qPCR. Moreover, in silico analyses have shown relevant signaling pathways associated with them suggesting a potential involvement of the dysregulated HERVs in these pathways and consequently in CLL development.

<p>PDF file, 654KB</p>

<p>PDF file, 22KB</p>

The microRNA 15a/16-1 cluster on chromosome 13 is commonly lost in chronic lymphocytic leukemia (CLL). Even though this deletion is considered to be a CLL-associated genomic aberration, loss of miR-15/16 occurs in 79% of primary acute myeloid leukemia (AML) and in patients with myelodysplastic syndrome (MDS) that transformed into AML. A second highly homologous locus, miR-15b/16-2, is present in both human and mice, and deletion of either miR-15/16 cluster in mice leads to CLL. Unexpectedly, when both loci are deleted, only 23% of miR-15/16 double knock out (DKO) mice develop various non-Hodgkin's lymphomas, whereas 77% develop AML. Consistent with this, DKO mice have an expanded Gr-1+CD11b+ granulocytic population in both bone marrow (BM) and spleen. These observations led us to hypothesize that the miR-15/16 clusters can act coordinately to regulate lineage determination and proliferation in early hematopoiesis. Their loss might influence leukemogenesis in CLL and AML by altering the number and function of hematopoietic stem cells (HSCs) and/or their downstream lineages and potentially increasing a population of preleukemic stem cells. To test this, using flow cytometry, we analyzed the numbers and frequency of HSCs and progenitors in DKO and C57BL/6 (B6) mice. We discovered major changes in HSCs and the common myeloid progenitors (CMP) but similar numbers of common lymphoid progenitors. Therefore, we focused on the myeloid lineage, finding that CD16/32-CD34- megakaryocyte/erythroid progenitors (MEP) were significantly increased in the Lin- cKit+ compartment of DKO mice (44.9% vs 29.8% P = 0.01), but CD16/32+CD34+ granulocyte-macrophage progenitors (GMP) were decreased (19.1% vs 40.1% P = 0.01). This was surprising since we also found that a GMP progeny population, CD11b+Gr-1+ cells, was enriched in DKO compared to B6 BM (60-70% vs 40%). To determine if this was a result of a differentiation defect in an earlier progenitor, we assessed the frequency of Lin-Sca1+cKit+ (LSK) populations, finding that DKO mice had significantly more CD150+CD48-CD34- LT-HSCs among LSK cells (14.3% vs 7.8% P = 0.03), and fewer CD150-CD48+ multipotent progenitors (MPP) (58.5% vs 68.6% P = 0.04). Of note, there was an increased absolute count for all progenitors analyzed, possibly due to an increase in BM cells and/or disproportional increases of certain cell types. Since the observed myeloproliferative phenotype could be due to 1) an absolute increase of progenitor cells; 2) malfunctioning progenitor cells that aberrantly differentiate and proliferate; 3) or both, we tested whether DKO LSK cells had distinct functional characteristics in vitro. Methylcellulose replating of LT-HSC and MPP in the presence of SCF, IL-3, and IL-6 indicated that DKO LT-HSC gave rise to consistently fewer colonies as compared to B6 LT-HSC (21.5 vs 37.2 colonies/100 cells plated P = 0.02). Unexpectedly, we found the opposite for MPP, as DKO MPP consistently exhibited higher colony-forming activity than B6 MPP (16.6 vs 5.1 colonies/100 cells plated P = 0.04) over the course of serial replating experiments. This was surprising in light of the significant decrease in MPP frequency we had observed by immunophenotyping. Furthermore, B6 MPP cells ceased forming colonies after 3 rounds of replating, whereas DKO MPP continued for 5 rounds, suggesting that the absence of miR-15/16 increased the self-renewal potential of the CD150-CD48+ MPP cells. This was further supported by immunophenotyping analysis showing increased LSK cells derived from DKO MPP colonies (25.8% vs 4.4% P = 0.03). In concordance with the initial observation, an increase in DKO MPP colony-derived CD11b+Gr-1+ cells was at least partly responsible for the myeloproliferative defect in the mature cell compartment (76.1% vs 56.9%P = 0.01). Together, these results suggest that in miR-15/16 DKO mice, the phenotypically defined MPP compartment contains leukemia-initiating cells. Overall, our findings reveal a novel role for the miR-15/16 clusters at the top of the hematopoietic hierarchy. Future experiments focusing on these DKO progenitors that appears to be endowed with leukemic stem cell potential may provide clues to understand how the targets of miR-15a, miR-15b and miR-16 orchestrate their effects on lineage commitment and how their absence may lead to initiation of AML and CLL. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

tRNA fragments (tRNA derived fragments or tRFs) are small single stranded RNA molecules derived from pre-tRNAs and mature tRNAs. tRFs have been known for a number of years, but previously they were believed to be not important products of tRNA degradation. tRFs can be unique, like tRF-1 s, or redundant, like tRF-3 s and tRF-5 s. Scientific interest in tRFs has drastically increased in the last 5 years. Many studies have found that tRFs are differentially expressed in many normal cellular processes as well as in transformed cancer cells. Dysregulation of tRFs expression have been reported in multiple major types of cancer including solid cancers and lymphoid malignancies. However the exact molecular role of these molecules is not entirely clear. A number of studies proposed that tRFs can work as microRNAs by targeting gene expression. Here we discuss recent studies showing differential expression of tRFs in many cancers as well as what is currently known about tRFs biological functions in cancer cells.

After publication of this Article the authors noticed errors in several figures. In Fig. 2b the Gapdh panels are incorrect. The lysates are identical to those used in Fig. 1b, therefore the Gapdh panels should be the same in both figures. In Fig. 3b the Gapdh panels for Ad-Fhit-wt and Ad-Fhit-Y114F are incorrect and have been replaced with scans from original films. In Fig. 4A the Gapdh panels are incorrect. The lysates are identical to those used in Fig. 3b, therefore the Gapdh panels should be the same in both figures. In Fig. 4Bb the Gapdh panels for Fhit siRNA were incorrect and have been replaced with scans from original films. All resupplied figures are provided below. In Fig. 5C several panels are incorrect. The Authors were unable to locate the original films for all of these panels so Fig. 5c has been deleted. The scientific conclusions of this paper have not been affected.

Significance 13q14.3 deletion is the most common genetic lesion identified in CLLs. This study shows that microdeletions affecting the miR-15a/16-1 cluster are more frequent than expected in all CLL cohorts and are prevalent in patients carrying a trisomy 12. Copy-number variation analysis and an experimental FISH analysis revealed that ∼34% of samples carry previously unidentified microdeletions of miR-15a/16-1 . These data may have clinical relevance for the successful stratification of patients for treatment.

Chronic lymphocytic leukemia (CLL) is the most common human leukemia, and dysregulation of tRNA-derived short noncoding RNA (tsRNA) (tRF-1) expression is an accompanying event in the development of this disease. tsRNAs are fragments originating from the 3′ end of tRNA precursors and do not contain mature tRNA sequences. In contrast to tsRNAs, mature tRFs (tRF-3s, tRF-5s, and internal tRFs) are produced from mature tRNA sequences and are redundant fragments. We investigated tsRNA expression in CLL and determined tsRNA signatures in indolent CLL and aggressive CLL vs. normal B cells. We noticed that both ts-43 and ts-44 are derived from distinct genes of pre-tRNA His , and are down-regulated in CLL 3- to 5-fold vs. normal B cells. Thus, we investigated expression levels of tRF-5 fragments from tRNA His in CLL samples and healthy controls, and determined that such fragments are down-regulated by 5-fold in CLLs vs. normal controls. Given these results, we investigated the expression of all mature tRFs in CLLs vs. normal controls. We found a drastic dysregulation of the expression of mature tRFs in CLL. In aggressive CLL, for the top 15 up-regulated fragments, linear fold change varied from 2,053- to 622-fold. For the top 15 down-regulated fragments in CLL, linear fold change varied from 314- to 52-fold. In addition, 964 mature tRFs were up-regulated at least 2-fold in CLL, while 701 fragments were down-regulated at least 2-fold. Similar results were obtained for indolent CLL. Our results suggest that mature tRFs may have oncogenic and/or tumor suppressor function in CLL.

By using chronic lymphocytic leukemia as target for discovery in cancer pathogenesis we discovered that the great majority of CLLs (75–85%) carry a deletion of miR-15a and miR-16-1 at 13q14. We also discovered that miR-15/16 are negative regulators of the BCL2 oncogene. Thus the loss of the two negative regulators causes BCL2 overexpression and leukemia. A corollary of this is that CLL is very sensitive to the anti BCL2 drug venetoclax that can induce complete remission in CLL patients. Since leukemia patients may carry billions of leukemia cells, it is quite likely that some (few) of the leukemic cells are resistant to venetoclax. Thus, since microRNAs have multiple targets, we looked for other proteins that may be overexpressed in CLL because of the low of miR-15/16. We discovered that ROR1 an embryonal antigen expressed on most (∼ 90%) CLL, but not on normal B cell, is also regulated by miR-15/16. Thus CLL cells are also sensitive to monoclonal antibodies against ROR1. Venetoclax and monoclonal antibodies against ROR1 act synergistically in killing CLL cells.

In 1984, we investigated the t(14;18) chromosomal translocations that frequently occur in patients with follicular lymphoma. We first identified a locus on chromosome 18 involved in these translocations with the chromosome 14 containing the immunoglobulin heavy chain locus. Within this region on chromosome 18, we then discovered a gene that we called BCL2, which was activated by the translocations. Since that time, many studies determined that BCL2 is one of the most important oncogenes involved in cancer by inhibiting apoptosis. In 2002, we studied 13q deletions in chronic lymphocytic leukemia (CLL) and found that the microRNA cluster miR-15a/miR-16-1 (miR-15/16) is deleted by 13q deletions. In 2005, we discovered that miR-15/16 function as tumor suppressors by directly targeting BCL2. Thus the loss of two negative regulators of BCL2 expression results in overexpression of BCL2. Very recently, a specific BCL2 inhibitor ABT-199 (Venetoclax) was developed and approved by FDA for CLL treatment. Thus it took 32 years from fundamental discovery of a critical oncogene to the development of a drug capable to cure CLL. In this review, we discuss the discovery, functions and clinical relevance of miR-15/16 and BCL2.

Chronic lymphocytic leukemia (CLL) is the most common adult leukemia. It is characterized by the accumulation of CD19+/CD5+ lymphocytes and can have variable outcomes. Richter syndrome (RS) is a lethal complication in CLL patients that results in aggressive B-cell lymphomas, and there are no tests to predict its occurrence. Because alterations in microRNA expression can predict the development and progression of several cancers, we investigated whether dysregulation of specific microRNAs can predict RS in CLL patients. Thus, we compared microRNA expression levels in samples from 49 CLL patients who later developed RS with samples from 59 CLL patients who did not. We found that high expression of miR-125a-5p or low expression of miR -34a-5p can predict ∼50% of RS with a false positive rate of ∼9%. We found that CLL patients predicted to develop RS show either an increase of miR-125a-5p expression (∼20-fold) or a decrease of miR-34a-5p expression (∼21-fold) compared with CLL patients that are not predicted to develop RS. Thus, miR-125a-5p and miR-34a-5p can be valuable predictor markers of RS and have the potential to provide physicians with information that can indicate the best therapeutic strategy for CLL patients.

Loss of miR-15/16 is the most common genetic lesion in chronic lymphocytic leukemia (CLL), promoting overexpression of BCL2, which factors in leukemia pathogenesis. Indeed, an inhibitor of Bcl2, venetoclcax, is highly active in the treatment of patients with CLL. However, single-agent venetoclcax fails to eradicate minimal residual disease in most patients. Accordingly, we were interested in other genes that may be regulated by miR-15/16, which may target other drivers in CLL. We found that miR-15/16 targets ROR1, which encodes an onco-embryonic surface protein expressed on the CLL cells of over 90% of patients, but not on virtually all normal postpartum tissues. CLL with high-level expression of ROR1 also have high-level expression of Bcl2, but low-to-negligible miR-15/16. Moreover, CLL cases with high-level ROR1 have deletion(s) at the chromosomal location of the genes encoding miR-15/16 (13q14) more frequently than cases with low-to-negligible ROR1, implying that deletion of miR-15/16 may promote overexpression of ROR1, in addition to BCL2. ROR1 is a receptor for Wnt5a, which can promote leukemia-cell proliferation and survival, and can be targeted by cirmtuzumab, a humanized anti-ROR1 mAb. We find that this mAb can enhance the in vitro cytotoxic activity of venetoclcax for CLL cells with high-level expression of ROR1, indicating that combining these agents, which target ROR1 and Bcl2, may have additive, if not synergistic, activity in patients with this disease.