Abstract
CK2 (Csnk2, casein kinase 2) is a Ser-Thr kinase composed by two catalytic (α) and two regulatory (β) subunits and involved in the regulation of various signaling cascades, which are critical for stem cell biology and hematopoietic development. However, a direct role for CK2 during blood cell differentiation is still undefined. Here, we examined the function of CK2 in erythropoiesis by using a hematopoietic-specific conditional knockout mouse model of the β regulatory subunit (Vav1-CRE x Csnk2β f/f mice). Since CK2β knockout mice died in utero, the study was carried out during gestation collecting fetuses from 12.5 to 17.5 days post conception (dpc) and performing the analysis on fetal liver. CK2β knockout fetuses were pale and hydropic, displayed a smaller liver, disarrayed vascularization and haemorrhages. Lack of CK2β caused depletion of hematopoietic/precursor cells, in particular of common lymphoid progenitors and megakaryocyte-erythrocyte progenitors. CK2β loss resulted to affect both early and late erythroid maturation and red cell viability. CK2β knockout contained lower numbers of TER119 positive cells, which displayed a down modulation of the surface expression of transferrin receptor (CD71) and an increased spontaneous apoptosis. Erythroid cells showed alterations in morphology compatible with myelodysplastic changes. Loss of CK2β caused alterations of erythroid cell proliferation, which was different depending on the stage of erythroid maturation: indeed, BrdU and 7AAD staining showed that less mature erythroid cells (CD71+Ter119-) had a lower rate of proliferation but a normal viability; on the contrary, more mature (CD71-Ter119+) erythroid cells suffered in part of apoptosis and in part accumulated in the S phase. RNA seq analysis performed on purified Ter119+ cells revealed upregulation of TP53 -associated genes as well as of Cdkn1a (p21); on the contrary, there was a down-modulation of Stat5 (an erythropoietin receptor down-stream effector) and genes involved in red cell survival and differentiation in particular c-kit and genes associated to the PI3/Akt pathway. The expression of adhesion molecules and surface carriers for inorganic cations/anionsimportant for the osmotic equilibrium and cell membrane integrity was also found markedly dysregulated. Real time quantitative PCR and Western Blot (WB) analyses confirmed the expression data of Cdkn1a, c-Kit, Bcl-xL, Jak-Stat5 as well as of Akt-Gata-1 axis. Gata-1, the key transcription factor for definitive erythropoiesis, was reduced in CK2β knockout mice as were its downstream target genes such as Alas-2, Lrf, Eklf, Epo-R, β-globin. Immature fetal globins accumulated. In order to find a molecular mechanism, we used an in vitro model of erythroid differentiation based on G1ER cells, an estrogen inducible GATA-1 null murine erythroblast cell line; the combined treatment of β-estradiol and inhibition of CK2 through the chemical inhibitor CX-4945 or RNA interference against CK2β confirmed the negative effect on differentiation. Western blot analysis indicated a potential role of the kinase in the regulation of Akt, Gata-1 and Stat5 protein stability. Moreover, the blockade or down modulation of CK2 caused changes in Gata-1 nuclear distribution with loss of the speckled pattern induced by β-estradiol. Thus, CK2 is a likely essential controller of GATA-1 transcriptional function. Altogether, our work demonstrates that CK2 is a master regulator of erythroid development, by impinging on Stat5, Akt and Gata-1 signaling and influencing red cell viability, bioenergetics, proliferation and maturation.
Disclosures
No relevant conflicts of interest to declare.
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