Mesenchymal stem cells (MSCs) have an inhibitory effect on tumor proliferation, but the precise mechanisms are not fully understood. Here, we identified DKK-1 (dickkopf-1), secreted by MSCs and acting as a negative regulator of WNT signaling pathway, to be one of the molecules responsible for the inhibitory effect. When DKK-1 was neutralized by anti-DKK-1 antibodies, or when the expression of DKK-1 was downregulated by RNA interference (RNAi), the inhibitory effects of MSCs on K562 cell proliferation were attenuated. We also provide evidence that the expression of DKK-1 by MSCs is regulated by NANOG, a transcriptional factor ubiquitously expressed in some stem cells. Using the Cellmax artificial capillary modules that eliminate the immunosuppressive properties of MSCs, we further showed that MSCs were able to inhibit proliferation of K562 cells in a humoral microenvironment. Meanwhile, we recapture this effect of MSCs on primary leukemic hematopoietic progenitors from patients. MSCs probably have a general inhibitory effect on their neighboring cells, including malignant cells, en route to achieving tissue homeostasis.

Some transcription factors that specifically bind double-stranded DNA appear to also function as RNA-binding proteins. Here, we demonstrate that the transcription factor Sox2 is able to directly bind RNA in vitro as well as in mouse and human cells. Sox2 targets RNA via a 60-amino-acid RNA binding motif (RBM) positioned C-terminally of the DNA binding high mobility group (HMG) box. Sox2 can associate with RNA and DNA simultaneously to form ternary RNA/Sox2/DNA complexes. Deletion of the RBM does not affect selection of target genes but mitigates binding to pluripotency related transcripts, switches exon usage and impairs the reprogramming of somatic cells to a pluripotent state. Our findings designate Sox2 as a multi-functional factor that associates with RNA whilst binding to cognate DNA sequences, suggesting that it may co-transcriptionally regulate RNA metabolism during somatic cell reprogramming.

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Bioassay-guided fractionation of a methanol extract of the seeds of Caesalpinia sappan led to the isolation of 12 new cassane-type diterpenes, caesalsappanins A-L (1-12). Their structures were elucidated on the basis of NMR and HRESIMS analysis, and the absolute configuration of compound 1 was determined by single-crystal X-ray crystallography. All isolated compounds were tested against a chloroquine-resistant Plasmodium falciparum strain for antiplasmodial activities and against a small panel of human cancer cell lines for antiproliferative activities. Compounds 7 and 8 displayed antimalarial activity against the chloroquine-resistant K1 strain of P. falciparum with IC50 values of 0.78 and 0.52 μM and selectivity indices of 17.6 and 16.4, respectively. Compound 10 showed antiproliferative activity against the KB cancer cell line with an IC50 value of 7.4 μM.

The growth inhibition of HSCs induced by MSCs through an arrest in the G(0)/G(1) phase of the cell cycle is partially mediated by secretion of TGF-beta3 and HGF. MSCs inhibit HSCs activation through decreasing phosphorylation of extracellular signal-regulated kinase (ERK) 1/2. These results further support MSCs may be used as a novel therapy for treating fibrotic diseases in human.