Rap1 signal modulators control the maintenance of hematopoietic progenitors in bone marrow and adult long‐term hematopoiesis

Abstract

Adult long‐term hematopoiesis depends on sustaining hematopoietic stem/progenitor cells ( HSPC ) in bone marrow ( BM ) niches, where their balance of quiescence, self‐renewal, and hematopoietic differentiation is tightly regulated. Although various BM stroma cells that produce niche factors have been identified, regulation of the intrinsic responsiveness of HSPC to the niche factors remains elusive. We previously reported that mice deficient for Sipa1 , a Rap1 GTP ase‐activating protein, develop diverse hematopoietic disorders of late onset. Here we showed that transplantation of BM cells expressing membrane‐targeted C3G (C3G‐F) , a Rap1 GTP / GDP exchanger, resulted in the progressive decline of the numbers of HSPC repopulated in BM with time and impaired long‐term hematopoiesis of all cell lineages. C3G‐F / HSPC were sustained for months in spleen retaining hematopoietic potential, but these cells inefficiently contributed to overall hematopoietic reconstitution. C3G‐F / HSPC showed enhanced proliferation and differentiation with accelerated progenitor cell exhaustion in response to stem cell factor ( SCF ). Using a Ba/F3 cell line, we confirmed that the increased basal Rap1 GTP levels with C3G‐F expression caused a markedly prolonged activation of c‐Kit receptor and downstream signaling through SCF ligation. A minor population of C3G‐F / HSPC also showed enhanced proliferation in the presence of thrombopoietin ( TPO ) compared to Vect / HSPC . Current results suggest an important role of basal Rap1 activation status of HSPC in their maintenance in BM for sustaining long‐term adult hematopoiesis.

C3G Regulates STAT3, ERK, Adhesion Signaling, and Is Essential for Differentiation of Embryonic Stem Cells

“…C3G is required for skeletal muscle and neuronal differentiation in vitro; [ 16 , 17 ]. Expression of constitutively active C3G in hematopoietic stem and progenitor cells enhanced their differentiation and depleted progenitor cell population in the spleen [ 18 ].…”

The SWI/SNF chromatin-remodeling subunit DPF2 facilitates NRF2-dependent antiinflammatory and antioxidant gene expression

“…Chromatin accessibility in BM LK cells showed loss of nearly half of the accessible peaks in Dpf2 Δ/Δ cells (27,271 of 60,147 peaks; Figure 6, D and E , and Supplemental Figure 6C ), mostly in intronic and intergenic regions ( Supplemental Figure 6D ), suggesting enhancer misregulation. We focused on the 7,400 peaks that lost assay for transposase-accessible chromatin using sequencing (ATAC-Seq) signal at least 2-fold in Dpf2 Δ/Δ LK cells, primarily located at introns and intergenic regions ( Supplemental Figure 6E ), and closely annotated to 3,420 genes enriched in critical pathways that regulate HSC proliferation and quiescence, including Rap1 ( 52 ), PI3K-AKT ( 53 ), and MAPK and RAS ( 54 ) signaling pathways ( Supplemental Figure 6F ). TF Motif analyses showed enrichment in NRF2/NFE2L2 binding motifs ( Figure 6F ), confirming loss of accessibility and transcription at antioxidant and antiinflammatory loci such as Nqo1 , Hmox1 , and Gclc ( Figure 6G ).…”

TAGLN2 promotes papillary thyroid carcinoma invasion via the Rap1/PI3K/AKT axis

“…These results demonstrated that TAGLN2 might regulate some upstream factors to activate the PI3K/AKT pathway in PTC. Nonetheless, studies demonstrate that Rap1 has an important regulatory effect on the PI3K/AKT pathway (Imai et al 2019). Rap1, a member of the Ras superfamily of small G proteins, has two states: an active GTP-bound state and an inactive GDP-bound state (Imai et al 2019).…”

“…Nonetheless, studies demonstrate that Rap1 has an important regulatory effect on the PI3K/AKT pathway (Imai et al 2019). Rap1, a member of the Ras superfamily of small G proteins, has two states: an active GTP-bound state and an inactive GDP-bound state (Imai et al 2019). Rap1 activation is reported in various cancers and is recognized as a central regulator of multiple malignant processes, including proliferation, invasion, angiogenesis, and adhesion (Shah et al 2019).…”