n together, these results imply that phosphorylation of C/EBPb at threonine 188 is critical for transcriptional activity in the context of the C/EBPa 19276073 promoter. Additional support for a role of phosphorylation in the control of C/EBPb function also comes from the findings of Roy et al. who recently demonstrated that MLK3 activates C/EBPb in response to IFN-c by a mechanism involving decreased phosphorylation of a specific serine residue within transactivation domain. Therefore, even if C/EBPb binds the cebpa and pparc2 promoters in DLK-depleted cells as efficiently as in control cells, a change in its phosphorylation state that would impair its function or interaction with transcriptional co-activators is also consistent with our results. In summary, the results presented in this report identify DLK, a MLK family member, as one of the key regulators of adipocyte differentiation. Although the exact mechanisms by which DLK controls this process remain to be identified, DLK action most likely takes place downstream of C/EBPb NVP-BGJ398 web DNA-binding to the cebpa and pparc2 promoters but upstream of transcription initiation. Materials and Methods Chemicals and antibodies Dexamethasone, 3-isobutyl-1-methylxanthine, insulin, protease inhibitors, the mouse monoclonal antibody raised against a-tubulin and all others common reagents were purchased from Sigma-Aldrich Ltd.. Rosiglitazone was purchased from Cayman Chemicals, via Cedarlane. The rabbit polyclonal antibody raised against Role of DLK in Adipogenesis Role of DLK in Adipogenesis the pLKO.1-based lentiviral human DLK shRNA vector using FuGENE 6 transfection reagent. Briefly, cells were incubated in DMEM supplemented with 10% FBS, antibiotics and transfection mix for 48 hours. Medium containing lentiviruses was then collected, treated with polybrene and filtered. 24 hours prior infection, 3T3-L1 cells were seeded at a density of 2.56104 9128839 cells/ml in 100-mm dishes. The next day, medium was removed and 1 ml of lentiviral suspension was added to the plates. Cells were incubated at 37uC with the lentiviral suspension for 1 hour, and 8.5 ml of DMEM supplemented with 10% BCS and antibiotics were added. 24 hours later, cells were washed once with PBS, and either trypsinised and reseeded into four 60-mm dishes in DMEM supplemented with 10% FBS and 2 mg/ml puromycin for selection or used as is. Media was changed every 2 days until cells reached confluency, after which they were induced to differentiate as mentioned above. Preparation of cell or tissue lysates and immunoblotting DLK was obtained from Abgent. The rabbit polyclonal antibodies raised against JNK, phospho-JNK, C/EBPa, C/EBPb, C/EBPd and PPARc were obtained from Santa-Cruz Biotechnology Inc.. The rabbit polyclonal antibody raised against adiponectin was obtained from Calbiochem. The rabbit polyclonal and mouse monoclonal antibodies raised against Erk, phospho-Erk, p38 and phospho-p38 were obtained from Cell Signaling Technology Inc.. The monoclonal antibody raised against fatty acid synthase was obtained from BD Biosciences. Cell culture and differentiation 3T3-L1 and 293T cells were grown in Dulbecco’s modified Eagle’s medium supplemented with 10% Bovine Calf Serum, 100 U/ml penicillin and 100 mg/ml streptomycin. To induce differentiation, two day-postconfluent cells were fed with DMEM supplemented with 10% FBS, 
1 mM dexamethasone, 0.5 mM IBMX and 5 mg/ml insulin for two days. Medium was then changed for DMEM supplemented with 10% FBS and 5 mg/ml insu