Phosphorylation of SOS1 on tyrosine 1196 promotes its RAC GEF activity and contributes to BCR-ABL leukemogenesis

Abstract

Son of Sevenless 1 (SOS1) is a dual guanine nucleotide exchange factor (GEF) that activates the small GTPases RAC and RAS. While the molecular mechanisms of RAS GEF catalysis have been unveiled, how SOS1 acquires RAC GEF activity and what is the physio-pathological relevance of this activity is much less understood. Here, we show that SOS1 is tyrosine phosphorylated on Y1196 by ABL. Phosphorylation of Y1196 controls SOS1 inter-molecular interaction, is required to promote the exchange of nucleotides on RAC in vitro, and for PDGF activation of RAC and RAC-dependent actin remodeling and cell migration. SOS1 is also phosphorylated on Y1196 by BCR-ABL in chronic myelogenous leukemic (CML) cells. Importantly, in these cells, SOS1 is required for BCR-ABL-mediated activation of RAC, cell proliferation and transformation in vitro and in a xenograft mouse model. Finally, genetic removal of Sos1 in bone marrow derived cells (BMDC) from Sos1fl/fl mice and infected with BCR-ABL causes a significant delay in the onset of leukemogenesis once BMDC are injected into recipient, lethally irradiated mice. Thus, SOS1 is required for full transformation and critically contribute to the leukemogenic potential of BCR-ABL.

Functional Specificity of the Members of the Sos Family of Ras-GEF Activators: Novel Role of Sos2 in Control of Epidermal Stem Cell Homeostasis

“…In previous reports we carried out successful ablation of floxed Sos1 alleles in mice, or cells derived thereof, through the induction of Cre recombinase with tamoxifen or 4-hydroxytamoxifen, respectively [ 11 , 13 , 14 , 16 , 17 ]. However, since tamoxifen appears to affect the viability of keratinocytes in culture even at low concentrations, we decided to test the efficiency of GFP-Adeno-Cre infection as an alternative method to accomplish Sos1 depletion in freshly isolated Sos1 KO and Sos1/2 KO primary keratinocytes.…”

“…Nevertheless, a number of reports dealing with functional analysis of different biological systems in these KO animal models support the functional prevalence of Sos1 over Sos2 in physiological processes such as cell proliferation and viability, migration, inflammation, or regulation of intracellular ROS levels [ 12 , 13 , 14 ]. Likewise, a dominant role of Sos1 has also been described in various pathological processes, including the abnormal constitutive activation of NFkB in most cancer cells [ 15 ], the development of BCR-ABL-driven leukemia, and, in particular, skin homeostasis and chemically-induced skin carcinogenesis [ 16 , 17 , 18 , 19 ]. On the other hand, more recent reports have also described a hierarchical requirement for Sos2 to mediate cell transformation driven by mutant RAS genes and a differential involvement of Sos2 in EGF-stimulated PI3K/AKT signal transmission [ 20 , 21 ].…”

Existence of reprogrammed lymphoma stem cells in a murine ALCL-like model

“…Retroviral titers were determined by transduction of NIH/ 3T3 cells (DSMZ) as described previously ( Supplementary Fig. 1) [23].…”

“…Briefly, 12-week-old male donor mice were treated once with 5-Fluorouracil (150 mg/kg) at day −4 and BM cells were harvested from tibia and femur. After preincubation overnight in BM media (DMEM, 30% FBS, 10 ng/ml mIL-3, 10 ng/ml mIL-6, 50 ng/ml mSCF), BM cells were infected with retroviral supernatant as described previously [23]. Infection efficiency was determined by flow cytometric analysis of EGFP expression.…”

SOS2 Comes to the Fore: Differential Functionalities in Physiology and Pathology

“…Somewhat surprisingly, adult SOS1-KO or SOS2-KO mice were perfectly viable, but double SOS1/2-DKO animals died very rapidly [ 19 ], demonstrating a critical contribution of the SOS2 isoform (at least when SOS1 is absent) at the level of full organismal survival and homeostasis, and thus opening new avenues for consideration of SOS2 as a functionally relevant player in mammalian RAS signaling pathways. In this regard, a number of recent functional studies of SOS1 and SOS2 using diverse genetic and pharmacological SOS ablation approaches have significantly clarified, during the last decade, the mechanistic details underlying the functional specificity/redundancy of the SOS1 and SOS2 GEFs in a wide array of tissues and cells, both under physiological and pathological conditions [ 20 , 21 , 22 , 23 , 24 , 25 ] (see [ 5 ] for a review).…”