title: mTORC1-dependent and -independent regulation of stem cell renewal, differentiation, and mobilization.
abstract: The Tuberous Sclerosis Complex component, TSC1, functions as a tumor suppressor via its regulation of diverse cellular processes, particularly cell growth. TSC1 exists in a complex with TSC2 and functions primarily as a key negative regulator of mammalian target of rapamycin complex 1 (mTORC1) signaling and protein synthesis, although the TSC1/TSC2 complex also shows mTORC1-independent outputs to other pathways. Here, we explored the role of TSC1 in various aspects of stem cell biology and dissected the extent to which TSC1 functions are executed via mTORC1-dependent versus mTORC1-independent pathways. Using hematopoietic stem cells (HSCs) as a model system, we demonstrate that somatic deletion of TSC1 produces striking stem cell and derivative effector cell phenotypes characterized by increased HSC cell cycling, mobilization, marked progressive depletion, defective long-term repopulating potential, and hematopoietic lineage developmental aberrations. On the mechanistic level, we further establish that TSC1 regulation of HSC quiescence and long-term repopulating potential and hematopoietic lineage development is mediated through mTORC1 signaling. In contrast, TSC1 regulation of HSC mobilization is effected in an mTORC1-independent manner, and gene profiling and functional analyses reveals the actin-bundling protein FSCN1 as a key TSC1/TSC2 target in the regulation of HSC mobilization. Thus, TSC1 is a critical regulator of HSC self-renewal, mobilization, and multilineage development and executes these actions via both mTORC1-dependent and -independent pathways.
authors.affiliation: Department of Medical Oncology, Belfer Foundation Institute for Innovative Cancer Science, Dana-Farber Cancer Institute, Boston, MA 02115, USA.
authors.forename: Boyi
authors.initials: B
authors.lastname: Gan
authors.forename: Ergün
authors.initials: E
authors.lastname: Sahin
authors.forename: Shan
authors.initials: S
authors.lastname: Jiang
authors.forename: Abel
authors.initials: A
authors.lastname: Sanchez-Aguilera
authors.forename: Kenneth L
authors.initials: KL
authors.lastname: Scott
authors.forename: Lynda
authors.initials: L
authors.lastname: Chin
authors.forename: David A
authors.initials: DA
authors.lastname: Williams
authors.forename: David J
authors.initials: DJ
authors.lastname: Kwiatkowski
authors.forename: Ronald A
authors.initials: RA
authors.lastname: DePinho
mesh_terms: D000818:Animals; D001853:Bone Marrow / Q000473:pathology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D002465:Cell Movement / Q000502:physiology*; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000502:physiology*; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism; D046912:Multiprotein Complexes; D010641:Phenotype; D011506:Proteins; D015398:Signal Transduction / Q000502:physiology; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D008840:Microfilament Proteins; D046912:Multiprotein Complexes; D011506:Proteins; D014157:Transcription Factors; C000624651:Tsc1 protein, mouse; C000624654:Tsc2 protein, mouse; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; C020324:fascin; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases