Flag-c-Myc HA-REG  Flag-c-Myc WT T58/S62A HA-REG  EGFP C Fig. S1 A B Supplementary Figure S1. Measure the degradation of c-Myc by REG . (A) Construction of LPDS was indicated. (B) Cells were transfected with LPDS empty vector together with REG . Transfected cells were treated with MG132 then the luciferase activity was measured. Data were presented as means ± S.D. (Student's t-test), the actual p values were examined using paired t- test. (C) Cells transfected with siRNA against REG  or FBW7 were transfected with LPDS-Myc. The luciferase activity was measured using Dual-Luciferase reporter system kit (Promega). Data were presented as means ± S.D. (Student's t-test), the actual p values were examined using paired t-test. (D) Flag-c-Myc (WT) and Flag-c-Myc (T58/62A) with and without REG  were transfected into 293T cells. c-Myc and REG  protein levels were shown by Western blotting. EGFP as internal control for transfection efficiency. D Firefly-Luc c-Myc Renilla-Luc IRES Firefly-Luc c-Myc Renilla-Luc REG  Renilla-Luc Degradation LPDS p=0.01 p=0.02 Vector REG  Relative Activity p= p= siNC siREG  siFBW7 LPDS-c-Myc

REG  +/+ -/- Relative mRNA Level Fig. S2 Supplementary Figure S2. Measure the mRNA level in REG  +/+ and REG  -/- MEFs. mRNA level of c-Myc in in REG  +/+ and REG  -/- MEFs was detected using qPCR. Data were presented as means ± S.D. (Student's t-test), the actual p values were examined using paired t-test. p=0.002

IB:Flag HA-c-Myc Flag- REG  WT K195R IP:Flag WCE IB:HA IB:Flag A C EGFP HA-c-Myc Flag-REG  Vector WT K195R HA-c-Myc IP: Flag GFP-REG  Flag-c-Myc – WT T58A S62A T58/S62A IB: REG  IB: Flag *IgG WCE IB: REG  IB: Flag GFP-REG  HA-c-Myc – WT IP:HA WCE IB: REG  IB: HA IB: REG  IB: HA E Fig. S3 D GST-REG  GST WCE Pull-Down c-Myc GST-REG  B FL-Myc Myc-Nick REG  EGFP IB: Myc274 antibody IB: REG  IB: EGFP Control REG  FL-Myc IB: Myc274 antibody REG  EGFP Control REG  IB: REG  IB: EGFP Sparse Dense F

Supplementary Figure S3. The interaction between c-Myc and REG . (A) 293T cells were co- transfected with Flag-c-Myc WT, T58A,T62A, T58/62A mutants and GFP-REG  as displayed. Cells were treated with MG132 before harvesting and cell lysates were subjected to immunoprecipitation using an anti-Flag antibody. The c-Myc protein levels were determined by Western blotting. (B) 293T cells were co-transfected with HA-c-Myc (WT) and HA-c-Myc (1-298) with REG  for 48 hours  Cell lysates were immunoprecipitated using an anti-HA antibody. The samples were evaluated using Western blotting. (C) HA-c-Myc and REG  were transfected into 293T cells under sparse and dense condition, respectively. The protein levels of c-Myc were measured by anti-c-Myc (274) antibody. (D) In vitro translated c-Myc proteins were incubated with the purified fragments of GST-fused REG  proteins, the interaction was analyzed using Western blotting. (E) 293T cells were co-transfected with HA-c-Myc, Flag-REG  and Flag-REG  K195R as indicated  Cell lysates were processed and then immunoprecipitated using an anti- Flag antibody. The interaction was examined using Western blotting. (F) HA-c-Myc and Flag- REG , REG  K195R were transfected into 293T cells together with EGFP. EGFP was indicator for transfection efficiency.

Flag-dMyc HA-dReg IP:HA WCE Flag-dMyc HA-dReg Flag-dMyc HA-dReg Flag-dMyc HA-dReg IP:Flag WCEHA-dReg Fig. S4 A B Supplementary Figure S4. Interaction between dMyc and dReg. (A-B) S2 cells were transfected with pUAST-HA-dMyc/pUAST-HA-dReg and simultaneously with Ubi-Gal4 constructs. Forty-eight hours later, cells were lysed in lysis buffer, followed by coimmunoprecipitation and Western blotting analyses with the indicated antibodies.