No abstract

bcl-x is a member of the bcl-2 gene family, which regulates apoptotic cell death in various cell lineages. There is circumstantial evidence suggesting that bcl-x might play a role in the apoptosis of erythroid lineage cells, although there is no direct evidence. In this study, we used Bcl-X null mouse embryonic stem (ES) cells, and showed that Bcl-X is indispensable for the production of both embryonic primitive erythrocytes (EryP) and adult definitive erythrocytes (EryD) at the end of their maturation. In vivo, bcl-x −/− ES cells did not contribute to circulating EryD in adult chimeric mice that were produced by blastocyst microinjection of the bcl-x −/− ES cells. bcl-x −/− EryP and EryD were produced by in vitro differentiation induction of ES cells on macrophage colony-stimulating factor–deficient stromal cell line OP9, and further analysis was carried out. The emergence of immature EryP and EryD from bcl-x −/− ES cells was similar to that from bcl-x +/+ ES cells. However, prominent cell death of bcl-x −/− EryP and EryD occurred when the cells matured. The data show that the antiapoptotic function of bcl-x acts at the very end of erythroid maturation.

STAT3 signaling constitutes an important negative feedback mechanism for the maintenance of immune homeostasis, a suppressive signal for the Th1 immune response in murine macrophages, and a cancer immune evasion signal in various immune cells. The strategy for STAT3 signal inhibition should be considered, because these features could impede effective cancer immunotherapy. We have evaluated the effects of STAT3 inactivation in dendritic cells (DCs) on immune responses in mice and humans. DCs derived from LysMcre/STAT3flox/flox mice displayed higher cytokine production in response to TLR stimulation, activated T cells more efficiently, and were more resistant to the suppression of cytokine production by cancer-derived immunosuppressive factors compared with DCs from control littermates. Antitumor activities of STAT3-depleted and control DCs were compared by intratumoral administration of gp70 Ag peptide-pulsed DCs in the therapeutic MC38 tumor model. Intratumoral administration of STAT3-depleted DCs significantly inhibited MC38 tumor growth of both injected and nontreated remote tumors. The inhibition was accompanied by an increase in gp70-specific T cell response as well as in systemic Th1 immune response. STAT3-depleted human DCs with adenoviral STAT3 short hairpin RNA were also capable of producing more cytokines with TLR stimulation and more resistant to cancer-derived factors, and they induced tumor Ag-specific T cells more efficiently than control DCs. The identified role of DC STAT3 signaling in both in vivo therapeutic tumor models in mice and in vitro-specific T cell induction in humans indicates that STAT3-inactivated DCs may be a promising approach for cancer immunotherapy.

The myb gene family has three members, c-myb, A-myb, and B-myb. A-myb mRNA is mainly expressed in testis and peripheral blood leukocytes. A-Myb can activate transcription from the promoter containing Myb-binding sites in all cells examined. In addition to the two domains (a DNA-binding domain and a transcriptional activation domain), two negative regulatory domains have been identified in A-Myb. These results indicate that A-Myb functions as a transcriptional activator mainly in testis and peripheral blood cells, and the regulatory mechanism of A-Myb activity is similar to that of c-Myb.