Peptide Biology Laboratories, Salk Institute for Biological Studies, La Jolla, CA 92037.
Department of Genetics, Institute for Diabetes, Obesity, and Metabolism, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104.
Proc Natl Acad Sci U S A. 2017 Oct 31;114(44):11739-11744. doi: 10.1073/pnas.1712616114. Epub 2017 Oct 16.
Populations of circulating immune cells are maintained in equilibrium through signals that enhance the retention or egress of hematopoietic stem cells (HSCs) from bone marrow (BM). Prostaglandin E2 (PGE2) stimulates HSC renewal and engraftment through, for example, induction of the cAMP pathway. Triggering of PGE2 receptors increases HSC survival in part via the PKA-mediated induction of the cAMP response element-binding protein (CREB) signaling pathway. PKA stimulates cellular gene expression by phosphorylating CREB at Ser133 and by promoting the dephosphorylation of the cAMP- responsive transcriptional coactivators (CRTCs). We show here that disruption of both CRTC2 and CRTC3 causes embryonic lethality, and that a single allele of either CRTC2 or CRTC3 is sufficient for viability. CRTC2 knockout mice that express one CRTC3 allele (CRTC2/3m mice) develop neutrophilia and splenomegaly in adulthood due to the up-regulation of granulocyte-colony stimulating factor (G-CSF); these effects are reversed following administration of neutralizing anti-G-CSF antiserum. Adoptive transfer of CRTC2/3m BM conferred the splenomegaly/neutrophilia phenotype in WT recipients. Targeted disruption of both CRTC2 and CRTC3 in stromal cells with a mesenchymal Prx1-Cre transgene also promoted this phenotype. Depletion of CRTC2/3 was found to decrease the expression of Suppressor of Cytokine Signaling 3 (SOCS3), leading to increases in STAT3 phosphorylation and to the induction of CEBPβ, a key regulator of the G-CSF gene. As small molecule inhibition of JAK activity disrupted CEBPβ induction and reduced G-CSF expression in CRTC2/3m stromal cells, our results demonstrate how cross-coupling between the CREB/CRTC and JAK/STAT pathways contributes to BM homeostasis.
循环免疫细胞群体通过增强造血干细胞（HSCs）从骨髓（BM）中保留或流出的信号来维持平衡。例如，前列腺素 E2（PGE2）通过诱导 cAMP 途径刺激 HSC 更新和植入。通过 PKA 介导的 cAMP 反应元件结合蛋白（CREB）信号通路的诱导，触发 PGE2 受体增加 HSC 存活。PKA 通过磷酸化 CREB 的 Ser133 并促进 cAMP 反应转录共激活因子（CRTCs）的去磷酸化来刺激细胞基因表达。我们在这里表明，CRTC2 和 CRTC3 的破坏都会导致胚胎致死，并且单个 CRTC2 或 CRTC3 等位基因足以维持生存。表达一个 CRTC3 等位基因的 CRTC2 敲除小鼠（CRTC2/3m 小鼠）在成年期由于粒细胞集落刺激因子（G-CSF）的上调而发展为中性粒细胞增多和脾肿大；这些影响在用中和抗 G-CSF 抗血清处理后逆转。CRTC2/3m BM 的过继转移赋予 WT 受体脾肿大/中性粒细胞增多表型。基质细胞中 CRTC2 和 CRTC3 的靶向破坏带有间充质 Prx1-Cre 转基因也促进了这种表型。发现 CRTC2/3 的耗竭导致抑制细胞因子信号转导 3（SOCS3）的表达增加，导致 STAT3 磷酸化增加，并诱导 G-CSF 基因的关键调节因子 CEBPβ。由于 JAK 活性的小分子抑制破坏了 CEBPβ 的诱导并减少了 CRTC2/3m 基质细胞中的 G-CSF 表达，我们的结果表明 CREB/CRTC 和 JAK/STAT 途径之间的交叉偶联如何有助于 BM 内稳态。
