Gab2 promotes hematopoietic stem cell maintenance and self-renewal synergistically with STAT5.
BACKGROUND
Grb2-associated binding (Gab) adapter proteins play major roles in coordinating signaling downstream of hematopoietic cytokine receptors. In hematopoietic cells, Gab2 can modulate phosphatidylinositol-3 kinase and mitogen associated protein kinase activities and regulate the long-term multilineage competitive repopulating activity of hematopoietic stem cells (HSCs). Gab2 may also act in a linear pathway upstream or downstream of signal transducer and activator of transcription-5 (STAT5), a major positive regulator of HSC function. Therefore, we aimed to determine whether Gab2 and STAT5 function in hematopoiesis in a redundant or non-redundant manner.


RESULTS
To do this we generated Gab2 mutant mice with heterozygous and homozygous deletions of STAT5. In heterozygous STAT5 mutant mice, deficiencies in HSC/multipotent progenitors were reflected by decreased long-term repopulating activity. This reduction in repopulation function was mirrored in the reduced growth response to early-acting cytokines from sorted double mutant c-Kit(+)Lin(-)Sca-1(+) (KLS) cells. Importantly, in non-ablated newborn mice, the host steady-state engraftment ability was impaired by loss of Gab2 in heterozygous STAT5 mutant background. Fetal liver cells isolated from homozygous STAT5 mutant mice lacking Gab2 showed significant reduction in HSC number (KLS CD150(+)CD48(-)), reduced HSC survival, and dramatic loss of self-renewal potential as measured by serial transplantation.


CONCLUSIONS
These data demonstrate new functions for Gab2 in hematopoiesis in a manner that is non-redundant with STAT5. Furthermore, important synergy between STAT5 and Gab2 was observed in HSC self-renewal, which might be exploited to optimize stem cell-based therapeutics.
Li
Geqiang
G
Division of Hematology-Oncology, Department of Medicine, Case Western Reserve University, Cleveland, Ohio, United States of America.
Wang
Zhengqi
Z
Miskimen
Kristy L
KL
Zhang
Yi
Y
Tse
William
W
Bunting
Kevin D
KD
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D000831:Animals, Newborn; D019070:Cell Lineage; D049109:Cell Proliferation; D002470:Cell Survival; D003114:Colony-Forming Units Assay; D005260:Female; D005434:Flow Cytometry; D005838:Genotype; D006410:Hematopoiesis; D018380:Hematopoietic Stem Cell Transplantation; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000378:metabolism*; D008099:Liver / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010750:Phosphoproteins / Q000172:deficiency* / Q000235:genetics; D050799:STAT5 Transcription Factor / Q000172:deficiency* / Q000235:genetics
D048868:Adaptor Proteins, Signal Transducing; C490894:Gab2 protein, mouse; D010750:Phosphoproteins; D050799:STAT5 Transcription Factor