Ability Of Leukemia Inhibitory Factor Research Articles

Activation of PDK-1 maintains mouse embryonic stem cell self-renewal in a PKB-dependent manner

The phosphatidylinositol 3′ kinase (PI3K) pathway is involved in many cellular processes including cell proliferation, survival and glucose transport, and is implicated in various disease states, such as cancer and diabetes. Although there have been numerous studies dissecting the role of PI3K signaling in different cell types and disease models, the mechanism by which PI3K signaling regulates embryonic stem (ES) cell fate remains unclear. It is believed that in addition to proliferation and tumorigenesis, PI3K activity may also be important for ES cell self-renewal. Paling et al. reported that the inhibition of PI3K led to a reduction in the ability of leukemia inhibitory factor to maintain self-renewal, causing cells to differentiate. Studies in our lab have revealed that ES cells completely lacking glycogen synthase kinase-3 (GSK-3) remain undifferentiated compared with wild-type ES cells. GSK-3 is negatively regulated by PI3K, suggesting that PI3K may have a vital role in maintaining pluripotency in ES cells through GSK-3. By using a modified Flp recombinase system, we expressed activated alleles of 3-phosphoinositide-dependent protein kinase-1 and protein kinase B to create stable, isogenic ES cell lines to further study the role of the PI3K signaling pathway in stem cell fate determination. In vitro characterization of the transgenic cell lines revealed a strong tendency toward the maintenance of pluripotency, and this phenotype was found to be independent of canonical Wnt signal transduction. In summary, PI3K signaling is sufficient to maintain the self-renewal and survival of stem cells. As this pathway is frequently mutationally activated in cancers, its effect on suppressing differentiation may contribute to its oncogenicity.

The Identification and Characterization of a STAT 1 Binding Site in the PPARγ2 Promoter

Interferon-γ (IFNγ) has been shown to decrease the expression of peroxisome proliferator activated receptor-γ (PPARγ) in fat cells by blocking the synthesis and increasing the degradation of this transcription factor. Since IFNγ is a potent activator of STAT 1, we searched for IFNγ-sensitive binding sites in the PPARγ promotors. A region of the murine PPARγ2 promoter was identified that bound nuclear protein from adipocyte nuclei that had been acutely treated with IFNγ. Supershift analysis revealed that STAT 1, and no other STATs present in the adipocyte nucleus, was capable of binding to this site within the PPARγ2 promoter. NIH 3T3 and 3T3-L1 cells were transiently transfected with a PPARγ2 promoter reporter construct, which contained the STAT 1 binding site. Treatment of these cells with IFNγ resulted in a decrease in reporter activity, demonstrating the modulation of the PPARγ2 promoter by IFNγ. We also examined the ability of leukemia inhibitory factor (LIF) to regulate binding at this site. LIF, a potent activator of STAT3 and a weak activator of STAT 1 in these cells, resulted in some binding to the IFNγ responsive element in the PPARγ2 promoter that was mediated by STAT 1. Therefore, we examined the ability of LIF to regulate PPARγ mRNA and observed that LIF, unlike IFNγ, had little effect on PPARγ expression. These results and our previous work suggest that cytokine induced STAT 1 homodimers modulate the transcriptional repression of PPARγ2 in adipocytes.

Establishment of SSEA-1- and Oct-4-Expressing Rat Embryonic Stem-like Cell Lines and Effects of Cytokines of the IL-6 Family on Clonal Growth

Here, we demonstrate long-term cultivation of alkaline phosphatase-positive rat embryonic stem-like (RES) cell lines. RES cells were characterized by their typical growth in highly compacted cell clusters, which were found to be sensitive against enzymatic dissociation. RES cells expressed stage-specific embryonic antigen-1 (SSEA-1) and transcription factor Oct-4, but Oct-4 mRNA was detected at lower levels compared to mouse ES cells. Once established to tissue culture, RES cells were able to grow in the absence of feeder cells under clonal conditions. Cytokines of the interleukin-6 family known to maintain the undifferentiated state of mouse ES cells were comparatively analyzed for their capacity to maintain the undifferentiated growth of two cell lines, RES-1 and RES-15, in a clonal assay. Rat ciliary neurotrophic factor (rCNTF), human oncostatin M (hOSM), and interleukin-6 and soluble interleukin-6 receptor (IL-6/sIL-6R) were found to support clonal growth of RES cells, but the cytokines did not reach the efficiency of the colony forming ability of leukemia inhibitory factor (LIF). When RES-1 and RES-15 cells were cultivated without feeder cells, SSEA-1 expression was maintained after clonal growth in the presence of LIF and LIF + rCNTF, respectively. Oct-4 mRNA was significantly detected in RES-15 cells when cultivated in the absence of feeder cells in media substituted by LIF and/or IL-6/sIL-6R, as well as without cytokines. In summary, rat embryonic stem-like cell lines could be established from rat blastocysts and were able to proliferate as undifferentiated alkaline phosphatase-positive cells. Embryonal stem cell properties, such as SSEA-1 and Oct-4 expression, were maintained by members of the IL-6 family of cytokines, but most significantly by LIF.

Leukemia inhibitory factor expression in human carotid plaques: possible mechanism for inhibition of large vessel endothelial regrowth.

One common feature of atherosclerotic plaques is the denudation of the endothelium covering the plaque and subsequent failure of endothelial regrowth in contrast to a marked proliferation of neocapillaries arising from the vasa vasorum within the medial wall. Previous studies in vitro have demonstrated the ability of leukemia inhibitory factor (LIF) to potently inhibit aortic endothelial cell growth while only slightly inhibiting the growth of adrenal cortex capillary endothelial cells. This selective effect of LIF on endothelial cells from different sources suggests that it may play a role in the failure of endothelial regrowth in atherosclerosis. Sections of human carotid endarterectomy samples were examined by in situ hybridization for LIF mRNA expression. In one-third of the samples (4/12) examined, cells within the atherosclerotic plaque exhibited LIF expression. Immunohistochemistry of serial sections suggested that the LIF-positive cells were activated macrophages. These results suggest that LIF may play a role in the pathogenesis of atherosclerosis, particularly the denudation of the large vessel endothelium.

Inhibition of differentiation by leukemia inhibitory factor distinguishes two induction pathways in P19 embryonal carcinoma cells

Abstract The ability of leukemia inhibitory factor (LIF) to block differentiation of P19 embryonal carcinoma (EC) cells under a variety of induction conditions was determined. LIF inhibits differentiation under several conditions which lead to endodermal and mesodermal cell lineages including skeletal and cardiac muscle. In contrast, LIF does not block differentiation when cells are induced under conditions which lead to neuro-ecto-dermal cell types including neurons and astroglial cells. These studies demonstrate that P19 EC cell differentiation can be divided into LIF sensitive and insensitive pathways which correlate with differentiation of endo-dermal/mesodermal and neuro-ectodermal cell types, respectively. The effect of LIF on mRNA levels for several genes which have previously been implicated in mediating differentiation in P19 EC cells was determined. LIF has no effect on the mRNA levels for retinoic acid receptor (RAR) α, RAR β, RAR γ, jun A, jun D, c- fos, or fra-1. In contrast LIF stimulates jun B mRNA expression by a factor of four to six under all induction conditions.