cAMP-induced PKCζ activation increases functional CXCR4 expression on human CD34+ hematopoietic progenitors

Abstract

Chemokines are key regulators of hematopoiesis and host defense. We report here that functional expression of the chemokine receptor CXCR4 on human immature CD34 ؉ hematopoietic progenitors was increased as a result of sustained elevation in cellular cAMP by dbcAMP and prostaglandin E2. This effect of cAMP was specifically mediated by PKC activity. CXCR4 expression and PKC activation by cAMP were decreased after the inhibition of cAMP effector-Rap1 by Spa1 overexpression. Interference with the activation of Rac1, a downstream target of Rap1, prevented the cAMPinduced increase in PKC activity and CXCR4 levels. Functional manifestation of the effects of cAMP-elevating agents revealed an increased ability of human CD34 ؉ cells to transmigrate the bone marrow (BM) endothelial layer and adhere to BM stroma in vitro, and it augmented the homing potential to the BM and spleens of immunodeficient mice in a Rac1-and a PKC-dependent manner. cAMP-and TNF␣-stimulated pathways converged in PKC-activated CXCR4 expression and MMP-2/MMP-9 secretion. cAMP treatment had a beneficial effect on CD34 ؉ cell survival in a PKC-mediated fashion. Taken IntroductionConsiderable effort has been invested in recent years toward understanding the mechanisms that govern hematopoietic stem/ progenitor cell trafficking and development. Chemokine stromal cell-derived factor-1 (SDF-1/CXCL12) is the only known powerful chemoattractant for defined populations of primitive human (CD34 ϩ CD38 Ϫ/low ) and murine (Sca-1 ϩ Thy-1 low c-kit ϩ Lin Ϫ ) hematopoietic progenitor cells. [1][2][3] The primary receptor for SDF-1, CXCR4, is expressed on a variety of immature and mature hematopoietic cells and on neuronal, endothelial, and epithelial cells. [4][5][6] Multiple studies have demonstrated major roles for SDF-1/CXCR4 interaction in human stem cell migration in vivo. Mice lacking either SDF-1 or CXCR4 exhibit several lethal defects, including impairment in hematopoiesis and stem cell seeding of the fetal BM. [7][8][9] We have previously shown that homing and engraftment of human CD34 ϩ CD38 Ϫ/low hematopoietic progenitors transplanted into immunodeficient mice are regulated by cell surface human CXCR4 expression and BMproduced murine SDF-1. 2,[10][11][12][13] The in vitro migratory capacity of enriched CD34 ϩ progenitors, particularly the expression and functionality of CXCR4 on these cells, directly correlates with clinical hematopoietic recovery after autologous stem cell transplantation. [14][15][16] Thus, understanding the mechanisms and molecular pathways that affect CXCR4 expression and cellular signaling might have important implications for clinical stem/ progenitor cell transplantation.Recently, we identified a specific isoform of the PKC family, atypical PKC, as a key regulator of SDF-1/CXCR4-activated signaling in human hematopoietic progenitors, demonstrating that ectopic PKC expression increases SDF-1-induced motility, whereas the inhibition of PKC activity impairs survival, proliferation, adhesion and, engraftment of immature CD34 ϩ proge...

cAMP Signaling in Leukocyte Transendothelial Migration

“…Moreover, cAMP-induced Rap1 signaling promotes homing of CD34 ϩ cells to the bone marrow. 42 Together, these data underscore the important stimulatory role of (localized) cAMP signaling in leukocyte adhesion and directional migration.…”

“…14 Finally, also in CD34 ϩ hematopoietic progenitor cells, cAMPmediated Rap1 activation results in increased ␣4␤1-mediated adhesion. 42 Together, these data indicate that Epac1-Rap1 signaling stimulates leukocyte adhesion, primarily through the activation of ␤1 integrins (Figure 2). …”

Plerixafor (AMD3100) and granulocyte colony-stimulating factor (G-CSF) mobilize different CD34+ cell populations based on global gene and microRNA expression signatures

“…26 PEG 2 also has been found to enhance the expression of CXCR4 on mouse CD34 ϩ cells. 27 This suggests that greater quantities of these progenitors are among plerixafor-mobilized and plerixafor plus G-CSF-mobilized CD34 ϩ cells than G-CSF-mobilized CD34 ϩ cells.…”

Rap1a Is a Key Regulator of Fibroblast Growth Factor 2-Induced Angiogenesis and Together with Rap1b Controls Human Endothelial Cell Functions

“…While Rap1a could also contribute to angiogenesis via regulation of pericytes/vascular smooth muscle cells (25,42,43), macrophages (32,49), and/or endothelial progenitor cells (6,20,37), data from the ex vivo aortic ring assay are supportive of a key role for Rap1 in endothelial cells. Increased vascular permeability is usually considered the first step in angiogenesis (37).…”