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Abstract: Interactions between the proteasome inhibitor, bortezomib, and the sphingosine kinase (SPK1) inhibitor, SKI, were examined in BCR/ABL human leukemia cells. Coexposure of K562 or chronic myeloid leukemia (CML) cells from patients to subtoxic concentrations of SKI (10μM) and bortezomib (100nM) resulted in a synergistic increase in caspase-3 cleavage and apoptosis. These events were associated with the downregulation of BCR–ABL and Mcl-1, and a marked reduction in SPK1 expression. In imatinib mesylate-resistant K562 cells that displayed decreased BCR–ABL expression, bortezomib/SKI treatment markedly increased apoptosis and inhibited colony-formation in association with the downregulation of Mcl-1. Finally, the bortezomib/SKI regimen also potently induced the downregulation of BCR/ABL and Mcl-1 in human leukemia cells. Collectively, these findings suggest that combining SKI and bortezomib may represent a novel strategy in leukemia, including apoptosis-resistant BCR–ABL+ hematologic malignancies. [Copyright &y& Elsevier]

Prokineticin-1 (PK1) has been identified as a mitogen-specific protein for the endothelium of steroidogenic glands. Here we report a novel function of PK1 in the regulation of multiple myeloma (MM) cells. PK1 activates multiple signals including mitogen-activated protein kinase (MAPK), PI3K-AKT, and Jak-STAT3, sphingosine kinase-1 (SPK1) in MM cells. Treatment of MM cells with PK1 causes a time- and dose-dependent phosphorylation of MAPK, AKT and STAT3 and upregulation of SPK1 expression and cellular activity. We also show that PK1 upregulates Mcl-1 expression in a time- and dose-dependent manner in human MM cell lines and in the cells of patients with MM. Pertussis toxin, a pan-PK1 receptor inhibitor, can block PK1-induced upregulation of Mcl-1, indicating it relates to a G-protein-coupled receptor. We also show that PK1 protects MM cells against apoptosis induced by starvation for fetal calf serum (FBS), or for FBS and IL-6. Taken together, PK1 activates multiple signaling pathways and, upregulates Mcl-1 expression, leading to proliferation and survival of MM cells. [ABSTRACT FROM AUTHOR]

Abstract: Sphingosine 1-phosphate (S1P) is a bioactive lysophospholipid which is known to induce diverse cellular responses through at least five G-protein-coupled receptors on various cell types. However, neither the distribution of S1P receptors nor the effects of S1P on multiple myeloma (MM) cells are fully understood. Here, we show that MM cells express the S1P receptors, S1P1, S1P2, and S1P3. Furthermore, S1P protects MM cells against Dex-induced apoptosis. Importantly, S1P upregulates Mcl-1 expression in a time- and concentration-dependent manner in human MM cell lines. Treatment of MM cells with pertussis toxin (PTX), a pan-S1P receptor inhibitor, results in blockage of S1P-induced upregulation of Mcl-1. These data demonstrate that S1P upregulates the expression of Mcl-1 and protects MM cells from Dex-induced apoptosis, providing the preclinical framework for novel therapeutics targeting at both Mcl-1 and/or S1P to improve the patient outcome in MM. [Copyright &y& Elsevier]

Abstract: MicroRNAs (miRNAs) are small, noncoding ribonucleic acids (ncRNAs), which regulate gene expression by targeting mRNAs for translational repression and degradation. Several lines of evidences have indicated that miRNAs act as tumor suppressors and oncogenes. However, the role of miRNAs in pathogenesis of multiple myeloma (MM) remains unclear. In this study, we examined the profile of miRNA expression of primary MM cells, using miRNA microarray and quantitative real-time polymerase chain reaction (qPCR) techniques. These results showed that in the bone marrow specimens analyzed, miRNA-29b was significantly downregulated. Similar results were also observed in human myeloma cell lines (HMCLs). Adenovirus-mediated overexpression of miR-29b induced apoptosis and elevated caspase-3 activation in HMCLs. Using a bioinformatics approach, we found a perfect complementarity between miRNA-29b and the 3′UTR of myeloid-cell-leukemia 1(Mcl-1). It is further confirmed that miRNA-29b downregulated the level of Mcl-1 without effect on the mRNA level using both qRT-PCR assays and Western blot analyses. Moreover, we observed that enforced miR-29b expression by using a retarget miRNA-29b expression vector (Ad5F11p-miR-29b) could induce apoptosis and elevate caspase-3 activation in HMCLs. Our results also indicated that miRNA-29b-induced apoptosis acted antagonistically with IL-6 in HMCLs. These findings suggest that miRNA-29b may play an important role in MM as a tumor suppressor. [Copyright &y& Elsevier]

Abstract: Members of the Spred gene family are negative regulators of the Ras/Raf-1/ERK pathway, which has been associated with several features of the tumor malignancy. However, the effect of Spred genes on hepatocellular carcinoma (HCC) remains uninvestigated. In the present work, we analyzed the in vitro and in vivo effects of Spred2 expression on the hepatic carcinoma cell line, SMMC-7721. In addition to attenuated ERK activation, which inhibited the proliferation and migration of unstimulated and HGF-stimulated SMMC-7721 cells. Adenovirus-mediated Spred2 overexpression induced the activation of caspase-3 and apoptosis, as well as reduced the expression level of Mcl-1. Most importantly, the knockdown of Spred2 markedly enhanced tumor growth in vivo. In conclusion, these results suggest that Spred2 could qualify as a potential therapeutic target in HCC. [Copyright &y& Elsevier]

Abstract: Spreds, a recently established class of negative regulators of the Ras–ERK (extracellular signal-regulated kinase) pathway, are involved in hematogenesises, allergic disorders and tumourigenesis. However, their role in hematologic neoplasms is largely unknown. Possible effects of Spreds on other signal pathways closely related to Ras–ERK have been poorly investigated. In this study, we investigated the in vitro effects of Spred2 on chronic myeloid leukemia (CML) cells. In addition to inhibiting the well-established Ras–ERK cascade, adenovirus-mediated Spred2 over-expression inhibits constitutive and stem cell factor (SCF)-stimulated sphingosine kinase-1 (SPHK1) and Mcl-1 expression, as well as inhibiting proliferation and inducing apoptosis in CML cells. In K562 cells and primary CML cells, imatinib induces endogenous Spred2 expression. Spred2 silencing by stable RNA interference partly protects K562 cells against imatinib-induced apoptosis. Together, these data implicate Spred2 in imatinib-induced cytotoxicity in CML cells, possibly by inhibiting the Ras–ERK cascade and the pro-survival signaling molecules SPHK1 and Mcl-1. These findings reveal potential targets for selective therapy of CML. [Copyright &y& Elsevier]