Figure 4. VitE directly binds and inhibits SHP1 activity after entering DCs via SCARB1.

A, Docking model of VitE (α-tocopherol) and auto-inhibitory SHP1 (PDB ID: 2B3O). Surface presentation of SHP1 in complex with VitE (cyan) bound in its central cavity, which is formed at the interface of all three domains of SHP1 (N-SH2, brown; C-SH2, blue; PTP, magenta).

B, Interactions of VitE with all three domains of SHP1 stabilized in its inhibitory conformation. Molecular forces implied in the interactions are hydrogen bonds with His112 (C-SH2) and Ser250 (PTP), hydrophobic interactions with His112 (C-SH2), Tyr214 (PTP) and Glu247 (PTP), and intramolecular hydrogen bonds between Ser 250 and Ser107.

C, The binding of VitE to purified SHP1 was analyzed by microscale thermophoresis (MST) binding assay. The apparent dissociation constant Kd is 39 ± 26 μM (mean of triplicates).

D, Relative tyrosine phosphatase activity of SHP1 immunoprecipitated from LPS (100ng/ml)-activated DC2.4 cells in the presence of indicated doses of VitE (mean of triplicates).

E, SHP1 tyrosine phosphatase activity in LPS (100ng/ml)-activated BMDCs (n=6) treated with vehicle or VitE (50μg/ml).

F, Normalized consensus protein-transcripts per million (pPTM) of SCARB1 in human immune cells from the Human Protein Atlas (HPA).

G, FACS analyses of pSHP1 expression in the vehicle- or VitE-treated BMDCs from wild type (WT, Scarb1^+/+) or Scarb1 knockout (Scarb1^−/−) C57BL/6 mice (n=3).

H, Quantification of T cell proliferation under coculture with WT or Scarb1^−/− DCs (n=5).

I, Model of VitE restoring TADCs function via SCARB1-SHP1 axis, leading to enhanced antitumor T cell immunity.

Error bars, s.e.m. Two-sided Student’s t-test (E, G, H). The statistical significance is defined by P-value: ns, no significant. *P < 0.05, **P < 0.01, ***P < 0.001.