TIS21/(BTG2) negatively regulates estradiol-stimulated expansion of hematopoietic stem cells by derepressing Akt phosphorylation and inhibiting mTOR signal transduction.
It has been known that 12-O-tetradecanoyl phorbol-13-acetate-inducible sequence 21 (TIS21), ortholog of human B-cell translocation gene 2, regulates expansions of stage-specific thymocytes and hematopoietic progenitors. In the present study, lineage-negative (Lin(-))/stem cell antigen-1-positive (Sca-1+)/c-Kit+ (LSK) cell content was significantly elevated in bone marrow (BM) of TIS21-knockout (TIS21(-/-)) female mice, suggesting 17beta-estradiol (E(2))-regulated progenitor expansion. E(2) induced DNA synthesis and cell proliferation of mouse embryonic fibroblasts (MEFs) isolated from TIS21(-/-) mice, but not wild type (WT). In contrast to WT, E(2) failed to activate protein kinase B (Akt) in the TIS21(-/-) MEFs, independent of extracellular signal-regulated kinase 1/2 (Erk1/2) activation. Despite attenuation of Akt activation, mammalian target of rapamycin (mTOR) was constitutively activated in the TIS21(-/-) MEFs. Furthermore, mitogen-activated protein kinase 1/2 inhibitor or knockdown of Erk1 could restore activation of Akt and downregulate mTOR. Immunoprecipitation showed Akt preferentially bound to phosphorylated Erk1/2 (p-Erk1/2) in TIS21(-/-) cells, but reconstitution of TIS21 inhibited their interaction. E(2)-injected TIS21(-/-) male mice also increased LSK cells in BM. Taken together, expansion of hematopoietic progenitors in TIS21(-/-) female mice might be through inhibition of Akt activation, and constitutive activation of mTOR via preferential binding of TIS21 to E(2)-induced p-Erk1/2, compared with that of Akt. Our results suggest that TIS21 plays a pivotal role in maintaining the hematopoietic stem cell compartment and hematopoiesis.
Department of Biochemistry and Molecular Biology, Ajou University School of Medicine, Suwon 443-721, Korea.
Bong Cho
BC
Kim
Min Sook
MS
Ryu
S Paul
SP
Oh
In Kyoung
IK
Lim
D000818:Animals; D002352:Carrier Proteins / Q000502:physiology*; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D004958:Estradiol / Q000494:pharmacology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D016147:Genes, Tumor Suppressor / Q000502:physiology*; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D017874:Immediate-Early Proteins / Q000502:physiology*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases; D025521:Tumor Suppressor Proteins
C489435:Btg2 protein, mouse; D002352:Carrier Proteins; D017874:Immediate-Early Proteins; D025521:Tumor Suppressor Proteins; D004958:Estradiol; D017853:Phosphotransferases (Alcohol Group Acceptor); C546842:MTOR protein, human; C546843:mTOR protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D048049:Extracellular Signal-Regulated MAP Kinases