title: DEPTOR is linked to a TORC1-p21 survival proliferation pathway in multiple myeloma cells.
abstract: We investigated the mechanism by which gene silencing of the mTOR inhibitor, DEPTOR, induces cytoreductive effects on multiple myeloma (MM) cells. DEPTOR knockdown resulted in anti-MM effects in several MM cell lines. Using an inducible shRNA to silence DEPTOR, 8226 MM cells underwent TORC1 activation, downregulation of AKT/SGK activity, apoptosis, cell cycle arrest and senescence. These latter cytotoxic effects were prevented by TORC1 paralysis (Raptor knockdown) but not by over-expression of AKT activity. In addition, DEPTOR knockdown-induced MM death was not associated with activation of the unfolded protein response, suggesting that enhanced ER stress did not play a role. In contrast, DEPTOR knockdown in 8226 cells induced p21 expression, independent of p53, and p21 knockdown prevented all of the cytotoxic effects following DEPTOR silencing. DEPTOR silencing resulted in p21 upregulation in additional MM cell lines. Furthermore, DEPTOR silencing in a murine xenograft model resulted in anti-MM effects associated with p21 upregulation. DEPTOR knockdown also resulted in a decreased expression of p21-targeting miRNAs and transfection of miRNA mimics prevented p21 upregulation and apoptosis following DEPTOR silencing. Use of a shRNA-resistant DEPTOR construct ruled out off-target effects of the shRNA. These results indicate that DEPTOR regulates growth and survival of MM cells via a TORC1/p21 pathway and suggest an involvement of p21-targeted miRNAs.
authors.affiliation: Department of Medicine, Hematology-Oncology, Greater Los Angeles VA Healthcare Center, Los Angeles, CA, USA ; UCLA School of Medicine, Greater Los Angeles VA Healthcare Center, Los Angeles, CA, USA.
authors.forename: Yonghui
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Department of Medicine, Hematology-Oncology, Greater Los Angeles VA Healthcare Center, Los Angeles, CA, USA ; UCLA School of Medicine, Greater Los Angeles VA Healthcare Center, Los Angeles, CA, USA.
authors.forename: Carolyne
authors.initials: C
authors.lastname: Bardeleben
authors.affiliation: Department of Medicine, Hematology-Oncology, Greater Los Angeles VA Healthcare Center, Los Angeles, CA, USA ; UCLA School of Medicine, Greater Los Angeles VA Healthcare Center, Los Angeles, CA, USA.
authors.forename: Patrick
authors.initials: P
authors.lastname: Frost
authors.affiliation: Department of Medicine, Hematology-Oncology, Greater Los Angeles VA Healthcare Center, Los Angeles, CA, USA ; UCLA School of Medicine, Greater Los Angeles VA Healthcare Center, Los Angeles, CA, USA.
authors.forename: Bao
authors.initials: B
authors.lastname: Hoang
authors.affiliation: Department of Medicine, Hematology-Oncology, Greater Los Angeles VA Healthcare Center, Los Angeles, CA, USA ; UCLA School of Medicine, Greater Los Angeles VA Healthcare Center, Los Angeles, CA, USA.
authors.forename: Yijiang
authors.initials: Y
authors.lastname: Shi
authors.affiliation: UCLA School of Medicine, Greater Los Angeles VA Healthcare Center, Los Angeles, CA, USA ; Jonsson Comprehensive Cancer Center, Greater Los Angeles VA Healthcare Center, Los Angeles, CA, USA.
authors.forename: Richard
authors.initials: R
authors.lastname: Finn
authors.affiliation: Department of Medicine, Hematology-Oncology, Greater Los Angeles VA Healthcare Center, Los Angeles, CA, USA ; UCLA School of Medicine, Greater Los Angeles VA Healthcare Center, Los Angeles, CA, USA ; Jonsson Comprehensive Cancer Center, Greater Los Angeles VA Healthcare Center, Los Angeles, CA, USA.
authors.forename: Joseph
authors.initials: J
authors.lastname: Gera
authors.affiliation: Department of Medicine, Hematology-Oncology, Greater Los Angeles VA Healthcare Center, Los Angeles, CA, USA ; UCLA School of Medicine, Greater Los Angeles VA Healthcare Center, Los Angeles, CA, USA ; Jonsson Comprehensive Cancer Center, Greater Los Angeles VA Healthcare Center, Los Angeles, CA, USA.
authors.forename: Alan
authors.initials: A
authors.lastname: Lichtenstein
keywords: AKT; DEPTOR; ER stress; Multiple Myeloma; mTORC1; p21