These results suggest a novel mechanism for adhesion regulation by a GJ-independent Cx26 function that correlates with prostate disease progression. The increased Cx26 expression during prostate cancer progression plays a role in adhesion regulation possibly through its interaction with FAK.

The Krü ppel-like C2/H2 zinc finger transcription factors (KLFs) control development and differentiation. Erythroid Krü ppel-like factor (EKLF or KLF1) regulates adult ␤-globin gene expression and is necessary for normal definitive erythropoiesis. KLF2 is required for normal embryonic Ey-and ␤h1-, but not adult ␤-globin, gene expression in mice. Both EKLF and KLF2 play roles in primitive erythroid cell development. To investigate potential interactions between these genes, EKLF/KLF2 double-mutant embryos were analyzed. EKLF ؊/؊ KLF2 ؊/؊ mice appear anemic at embryonic day 10.5 (E10.5) and die before E11.5, whereas single-knockout EKLF ؊/؊ or KLF2 ؊/؊ embryos are grossly normal at E10.5 and die later than EKLF ؊/؊ KLF2 ؊/؊ embryos. At E10.5, Ey-and ␤h1-globin mRNA is greatly reduced in EKLF ؊/؊ KLF2 ؊/؊ , compared with EKLF ؊/؊ or KLF2 ؊/؊ embryos, consistent with the observed anemia. Light and electron microscopic analyses of E9.5 EKLF ؊/؊ KLF2 ؊/؊ yolk sacs, and cytospins, indicate that erythroid and endothelial cells are morphologically more abnormal than in either single knockout. EKLF IntroductionKrüppel-Like factors (KLFs) are a family of DNA-binding proteins with sequence homology to the Drosophila transcription factor, Krüppel. KLFs have 3 C2/H2 zinc finger domains and share conserved residues located primarily within these domains. 1,2 Erythroid Krüppel-Like factor (EKLF or KLF1) was the first of 17 KLFs to be identified in mouse and man. 3 It is expressed specifically in erythroid cells and positively regulates the adult ␤-globin gene. 3,4 EKLF Ϫ/Ϫ mice develop fatal anemia during definitive (fetal liver) erythropoiesis, due to a defect in the maturation of red blood cells, and die by embryonic day 16 (E16). [5][6][7] Several other members of the KLF family, including KLF2 (lung Krüppel-like factor, LKLF), also are expressed in erythroid cells. [8][9][10][11] Based on phylogenetic analyses, the zinc finger domains of KLF2 and EKLF are very similar. 1,2,12,13 KLF2 Ϫ/Ϫ mice die between E12.5 and E14.5 due to heart failure and severe hemorrhaging, caused by defects in vascular endothelial cells and in stabilization of immature vessels by recruited smooth muscle cells. 14,15 Prior to E12.5, KLF2 Ϫ/Ϫ embryos have normal vasculogenesis and angiogenesis. 14,15 KLF2 also plays an important role in hematopoietic cell biology. We reported that KLF2 is essential for primitive (embryonic yolk sac) erythropoiesis and positively regulates the embryonic ␤-like globin genes in vivo. E10.5 KLF2 Ϫ/Ϫ primitive erythroid cells have abnormal morphology. 9 KLF2 also regulates T-cell activation. Deficiency of KLF2 leads to a decrease in the peripheral T-cell pool 16 due to defective thymocyte emigration. 17 Overexpression of KLF2 in mice inhibits proinflammatory activation of peripheral blood monocytes. 18 It was initially reported that EKLF does not affect embryonic/ fetal globin gene expression. Interestingly, however, EKLF is expressed very early in mouse and chicken development, as early as the primitive streak stage, fo...

Krüppel-like factor 2 (KLF2) is expressed in endothelial cells in the developing heart, particularly in areas of high shear stress, such as the atrioventricular (AV) canal. KLF2 ablation leads to myocardial thinning, high output cardiac failure and death by mouse embryonic day 14.5 (E14.5) in a mixed genetic background. This work identifies an earlier and more fundamental role for KLF2 in mouse cardiac development in FVB/N mice. FVB/N KLF2−/− embryos die earlier, by E11.5. E9.5 FVB/N KLF2−/− hearts have multiple, disorganized cell layers lining the AV cushions, the primordia of the AV valves, rather than the normal single layer. By E10.5, traditional and endothelial-specific FVB/N KLF2−/− AV cushions are hypocellular, suggesting that the cells accumulating at the AV canal have a defect in endothelial to mesenchymal transformation (EMT). E10.5 FVB/N KLF2−/− hearts have reduced glycosaminoglycans in the cardiac jelly, correlating with the reduced EMT. However, the number of mesenchymal cells migrating from FVB/N KLF2−/− AV explants into a collagen matrix is reduced considerably compared to wild-type, suggesting that the EMT defect is not due solely to abnormal cardiac jelly. Echocardiography of E10.5 FVB/N KLF2−/− embryos indicates that they have abnormal heart function compared to wild-type. E10.5 C57BL/6 KLF2−/− hearts have largely normal AV cushions. However, E10.5 FVB/N and C57BL/6 KLF2−/− embryos have a delay in the formation of the atrial septum that is not observed in a defined mixed background. KLF2 ablation results in reduced Sox9, UDP-glucose dehydrogenase (Ugdh), Gata4 and Tbx5 mRNA in FVB/N AV canals. KLF2 binds to the Gata4, Tbx5 and Ugdh promoters in chromatin immunoprecipitation assays, indicating that KLF2 could directly regulate these genes. In conclusion, KLF2−/− heart phenotypes are genetic background-dependent. KLF2 plays a role in EMT through its regulation of important cardiovascular genes.

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Objective A pro-apoptotic BH3-only protein BIM (BCL-2 interacting mediator of cell death) can link cytokine receptor signaling with the apoptotic machinery in hematopoietic cells. We investigated here the role of BIM in erythropoietin (Epo)-mediated survival in erythroid cells. Methods We down-regulated BIM in Epo-dependent HCD57 erythroid cells with shRNA, and used Real-time PCR, Western blots, and flow cytometry to characterize BIM expression and apoptosis. Hematologic analyses of BIM-deficient (Bim−/−) mice were conducted. Results BIM expression increases in primary murine erythroid cells and HCD57 cells deprived of Epo. Whereas Bim mRNA increased less than 2-fold, BIM protein increased more than 10-fold after Epo withdrawal, suggesting post-transcriptional regulation of BIM. Epo treatment resulted in rapid phosphorylation of BIM at Serine 65 and phosphorylation correlated with degradation of BIM. Inhibition of ERK (extracellular signal-regulated kinase) by a MEK/ERK inhibitor, U0126, blocked both phosphorylation and degradation of BIM, resulting in apoptosis. Treatment with a proteasome inhibitor, MG-132, also blocked degradation of phosphorylated BIM. Down-regulation of BIM with the shRNA resulted in HCD57 cells more resistant to apoptosis induced by either Epo withdrawal or ERK inhibition. Although we observed no significant changes in the number of erythrocytes or reticulocytes in the circulation of Bim−/− mice, erythroid progenitors from bone marrow in Bim−/− mice were reduced in number and more resistant to apoptosis induced by U0126 MEK/ERK inhibitor. Conclusion Epo protects erythroid cells from apoptosis in part through ERK-mediated phosphorylation followed by proteasomal degradation of BIM.