Levels of Smad7 regulate Smad and mitogen activated kinases (MAPKs) signaling and controls erythroid and megakaryocytic differentiation of erythroleukemia cells

SMAD7 polymorphisms and colorectal cancer risk: a meta-analysis of case-control studies

Mothers against decapentaplegic homolog 7 (SMAD7) inhibits the transforming growth factor-β (TGF-β) signaling pathway, which regulates carcinogenesis and cancer progression. A number of studies have reported that SMAD7 polymorphisms (rs4464148, rs4939827, and rs12953717) are associated with colorectal cancer (CRC) risk, but the results from these studies remain conflicting. To determine a more precise estimation of the relationship between SMAD7 and CRC, we undertook a large-scale meta-analysis of 63 studies, which included a total of 187,181 subjects (86,585 cases and 100,596 controls). The results of our meta-analysis revealed that the C allele of rs4464148 [CC vs. TT+TC, odds ratio (OR) =1.23, 95% confidence interval (CI): 1.14–1.33, P < 0.01], the T allele of rs4939827 [TT vs. CC+TC, odds ratio OR=1.15, 95%CI:1.07–1.22, P < 0.01] and the T allele of rs12953717 [TT vs. CC+TC, OR =1.22, 95%CI:1.16–1.29, P < 0.01] were all associated with the increased CRC risk. Subgroup analysis according to ethnicity showed rs4464148 and rs12953717 were associated with the risk of CRC in both Caucasians and Asians, whereas rs4939827 was a risk polymorphism for CRC specifically in Caucasians. In summary, this large-scale meta-analysis indicated that SMAD7 polymorphisms (rs4464148, rs4939827, and rs12953717) correlate with CRC.

The Transforming Growth Factor Beta 1/SMAD Signaling Pathway Involved in Human Chronic Myeloid Leukemia

Transforming growth factor beta 1 (TGF-β1) is the prototypic member of a large family of structurally related pleiotropic-secretedcytokines. The TGF-β1/SMAD signaling pathway usually participates in a wide range of cellular processes such as growth, proliferation, differentiation and apoptosis. Upon binding onTGF-β1, the dimerized TGF-β type II receptors recruit and phosphorylate the TGF-β type I receptors, which phosphorylate the receptor-regulated SMAD (SMAD2 and SMAD3) presented by the SMAD anchor for receptor activation.

The phosphorylated receptor-regulated SMAD form heterologous complexes with the common-mediator SMAD (SMAD4) and subsequently translocate into the nucleus, where they interact with other transcription factors to regulate the expression of target genes. This multi-functional signaling pathway modulated by various elements with complex mechanisms at different levels is also inevitably involved in cancer. We herein present data on the role of the TGF-β1/SMAD signaling pathway in human chronic myeloid leukemia and explain the potent biological effects of TGF-β1 on leukemia cells. The paper is based on a review of articles selected from Cancerline and Medline data bases.

The constitutively active tyrosine kinase produced by the specific Bcr-Abl fusion gene on the Philadelphia chromosome can enhance the resistance of malignant cells to TGF-β1-induced growth inhibition and apoptosis, which contributes to enhancement of proteasomal degradation of p27. However, overexpression of the EVI1 gene, which is also caused by Bcr-Abl, can recruit the C-terminal binding protein and histone deacetylase to prevent the MH2 domain on SMAD3. The later is essential for transcription activation on target genes and leads to blockage of the TGF-β1/SMAD signaling pathway.

Some studies have indicated that certain therapeutic agents applied in clinical treatment can inhibit proliferation and promote differentiation of leukemia cells by way of modulation of the TGF-β1/SMAD signal pathway. For example, arsenic trioxide can promote specific degradation of the AML1/MDS1/EVI1 oncoprotein and inhibit the proliferation of leukemia cells. However, specific histone deacetylase inhibitors can interrupt the effect of histone deacetylase to alleviate EVI1-mediated suppression of TGF-β1/SMAD signaling. The tyrosine kinase inhibitor in the target therapy of chronic myeloid leukemia can effectively inhibit the tyrosine kinase activity of Bcr-Abl and induce suppression on the TGF-β1/SMAD signaling pathway.

The TGF-β1/SMAD signaling pathway plays an important role in chronic myeloid leukemia cells and leads the leukemia cells to growth inhibition, differentiation and apoptosis. The positive influence of the TGF-β1/SMAD signaling pathway in chronic myeloid leukemia is fairly significant, and its potential effects in clinical treatment will bring about definite benefits.

Since it is a complex signaling pathway widely involved in many aspects of cellular activities, further study and comprehensive analysis of the TGF-β1/SMAD signaling pathway are imperative and will have a guiding significance in research and clinical applications. It is an exciting area for future research. Free full text available at www.tumorionline.it

Involvement of TGF-β1/Smad3 Signaling in Carbon Tetrachloride-Induced Acute Liver Injury in Mice

Transforming growth factor-beta1 (TGF-β1) is a major factor in pathogenesis of chronic hepatic injury. Carbon tetrachloride (CCl4) is a liver toxicant, and CCl4-induced liver injury in mouse is a classical animal model of chemical liver injury. However, it is still unclear whether TGF-β1 is involved in the process of CCl4-induced acute chemical liver injury. The present study aimed to evaluate the role of TGF-β1 and its signaling molecule Smad3 in the acute liver injury induce by CCl4. The results showed that CCl4 induced acute liver injury in mice effectively confirmed by H&E staining of liver tissues, and levels of not only liver injury markers serum ALT and AST, but also serum TGF-β1 were elevated significantly in CCl4-treated mice, compared with the control mice treated with olive oil. Our data further revealed that TGF-β1 levels in hepatic tissue homogenate increased significantly, and type II receptor of TGF-β (TβRII) and signaling molecules Smad2, 3, mRNA expressions and Smad3 and phospho-Smad3 protein levels also increased obviously in livers of CCl4-treated mice. To clarify the effect of the elevated TGF-β1/Smad3 signaling on CCl4-induced acute liver injury, Smad3 in mouse liver was overexpressed in vivo by tail vein injection of Smad3-expressing plasmids. Upon CCl4 treatment, Smad3-overexpressing mice showed more severe liver injury identified by H&E staining of liver tissues and higher serum ALT and AST levels. Simultaneously, we found that Smad3-overexpressing mice treated with CCl4 showed more macrophages and neutrophils infiltration in liver and inflammatory cytokines IL-1β and IL-6 levels increment in serum when compared with those in control mice treated with CCl4. Moreover, the results showed that the apoptosis of hepatocytes increased significantly, and apoptosis-associated proteins Bax, cytochrome C and the cleaved caspase 3 expressions were up-regulated in CCl4-treated Smad3-overexpressing mice as well. These results suggested that TGF-β1/Smad3 signaling was activated during CCl4-induced acute liver injury in mice, and Smad3 overexpression aggravated acute liver injury by promoting inflammatory cells infiltration, inflammatory cytokines release and hepatocytes apoptosis. In conclusion, the activation of TGF-β signaling contributes to the CCl4-induced acute liver injury. Thus, TGF-β1/Smad3 may serve as a potential target for acute liver injury therapy.

Voltage-Gated K+ Channel, Kv3.3 Is Involved in Hemin-Induced K562 Differentiation

Voltage-gated K⁺ (K_v) channels are well known to be involved in cell proliferation. However, even though cell proliferation is closely related to cell differentiation, the relationship between K_v channels and cell differentiation remains poorly investigated. This study demonstrates that K_v3.3 is involved in K562 cell erythroid differentiation. Down-regulation of K_v3.3 using siRNA-K_v3.3 increased hemin-induced K562 erythroid differentiation through decreased activation of signal molecules such as p38, cAMP response element-binding protein, and c-fos. Down-regulation of K_v3.3 also enhanced cell adhesion by increasing integrin β3 and this effect was amplified when the cells were cultured with fibronectin. The K_v channels, or at least K_v3.3, appear to be associated with cell differentiation; therefore, understanding the mechanisms of K_v channel regulation of cell differentiation would provide important information regarding vital cellular processes.

Activin A induction of erythroid differentiation sensitizes K562 chronic myeloid leukemia cells to a subtoxic concentration of imatinib

Chronic myeloid leukemia (CML) is a hematopoietic stem/progenitor cell disorder in which Bcr-Abl oncoprotein inhibits cell differentiation. Differentiation induction is considered an alternative strategy for treating CML. Activin A, a member of the transforming growth factor-β superfamily, induces erythroid differentiation of CML cells through the p38 MAPK pathway. In this study, treatment of the K562 CML stem/progenitor cell line with activin A followed by a subtoxic concentration of the Bcr-Abl inhibitor imatinib strongly induced growth inhibition and apoptosis compared with simultaneous treatment with activin A and imatinib. Imatinib-induced growth inhibition and apoptosis following activin A pretreatment were dose- and time-dependent. Imatinib-induced growth inhibition and apoptosis were also dependent on the pretreatment dose of activin A. More than 90% of the activin A-induced increases in glycophorin A-positive cells were sensitive to imatinib. However, only some of original glycophorin A-positive cells in the activin A treatment group were sensitive to imatinib. Sequential treatment with activin A and imatinib decreased Bcr-Abl, procaspase-3, Mcl-1, and Bcl-xL and also induced cleavage of procaspase-3/poly(ADP-ribose)polymerase. The reduction of erythroid differentiation in p38 MAPK dominant-negative mutants or by short hairpin RNA knockdown of p38 MAPK decreased the growth inhibition and apoptosis mediated by sequential treatment with activin A and imatinib. Furthermore, the same inhibition level of multidrug resistance 1 expression was observed in cells treated with activin A alone, treated sequentially with activin A and imatinib, or treated simultaneously with activin A and imatinib. The p38 MAPK inhibitor SB-203580 can restore activin A-inhibited multidrug resistance 1 expression. Taken together, our results suggest that a subtoxic concentration of imatinib could exhibit strong cytotoxicity against erythroid-differentiated K562 CML cells.

Smad7: not only a regulator, but also a cross-talk mediator of TGF-β signalling

TGF-β (transforming growth factor-β) is a pleiotropic cytokine regulating diverse cellular processes. It signals through membrane-bound receptors, downstream Smad proteins and/or other signalling mediators. Smad7 has been well established to be a key negative regulator of TGF-β signalling. It antagonizes TGF-β signalling through multiple mechanisms in the cytoplasm and in the nucleus. Smad7 can be transcriptionally induced by TGF-β and other growth factors and serves as an important cross-talk mediator of the TGF-β signalling pathway with other signalling pathways. Accordingly, it plays pivotal roles in embryonic development and adult homoeostasis, and altered expression of Smad7 is often associated with human diseases, such as cancer, tissue fibrosis and inflammatory diseases.

Gene Expression Differences between Enriched Normal and Chronic Myelogenous Leukemia Quiescent Stem/Progenitor Cells and Correlations with Biological Abnormalities

In comparing gene expression of normal and CML CD34+ quiescent (G0) cell, 292 genes were downregulated and 192 genes upregulated in the CML/G0 Cells. The differentially expressed genes were grouped according to their reported functions, and correlations were sought with biological differences previously observed between the same groups. The most relevant findings include the following. (i) CML G0 cells are in a more advanced stage of development and more poised to proliferate than normal G0 cells. (ii) When CML G0 cells are stimulated to proliferate, they differentiate and mature more rapidly than normal counterpart. (iii) Whereas normal G0 cells form only granulocyte/monocyte colonies when stimulated by cytokines, CML G0 cells form a combination of the above and erythroid clusters and colonies. (iv) Prominin-1 is the gene most downregulated in CML G0 cells, and this appears to be associated with the spontaneous formation of erythroid colonies by CML progenitors without EPO.

Analysis of microRNA transcriptome by deep sequencing of small RNA libraries of peripheral blood

Background

MicroRNAs are a class of small non-coding RNAs that regulate mRNA expression at the post - transcriptional level and thereby many fundamental biological processes. A number of methods, such as multiplex polymerase chain reaction, microarrays have been developed for profiling levels of known miRNAs. These methods lack the ability to identify novel miRNAs and accurately determine expression at a range of concentrations. Deep or massively parallel sequencing methods are providing suitable platforms for genome wide transcriptome analysis and have the ability to identify novel transcripts.

Results

The results of analysis of small RNA sequences obtained by Solexa technology of normal peripheral blood mononuclear cells, tumor cell lines K562 and HL60 are presented. In general K562 cells displayed overall low level of miRNA population and also low levels of DICER. Some of the highly expressed miRNAs in the leukocytes include several members of the let-7 family, miR-21, 103, 185, 191 and 320a. Comparison of the miRNA profiles of normal versus K562 or HL60 cells revealed a specific set of differentially expressed molecules. Correlation of the miRNA with that of mRNA expression profiles, obtained by microarray, revealed a set of target genes showing inverse correlation with miRNA levels. Relative expression levels of individual miRNAs belonging to a cluster were found to be highly variable. Our computational pipeline also predicted a number of novel miRNAs. Some of the predictions were validated by Real-time RT-PCR and or RNase protection assay. Organization of some of the novel miRNAs in human genome suggests that these may also be part of existing clusters or form new clusters.

Conclusions

We conclude that about 904 miRNAs are expressed in human leukocytes. Out of these 370 are novel miRNAs. We have identified miRNAs that are differentially regulated in normal PBMC with respect to cancer cells, K562 and HL60. Our results suggest that post - transcriptional processes may play a significant role in regulating levels of miRNAs in tumor cells. The study also provides a customized automated computation pipeline for miRNA profiling and identification of novel miRNAs; even those that are missed out by other existing pipelines. The Computational Pipeline is available at the website: http://mirna.jnu.ac.in/deep_sequencing/deep_sequencing.html