*2.9. Lys Depletion and Supplementation*

After a 24 h period to allow adhesion, cells were starved for 6 h in FBS- and Lys-free DMEM/F12 medium. Then, the cells were cultured in 500 μmol/L Lys (control) and 0 μmol/L Lys (Lys deficiency) DMEM/F12 medium with 10% FBS for 24, 48 and 72 h to investigate cell proliferation. For proliferation rescue, due to the extreme decrease in proliferation after Lys deficiency for 48 h, we added sufficient Lys for another 72 h at this point. Lys concentrations in DMEM/F12, FBS and culture medium are displayed in Table S3.

#### *2.10. Cell Proliferation Assay*

For the 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay, 20 μL 5 mg/mL MTT solution (Sigma-Aldrich, St. Louis, MO, USA) was added to each well and incubated for 4 h. Then, the plates were centrifuged at 1400× *g* for 15 min at 25 ◦C. A total of 150 μL dimethylsulfoxide (DMSO) working solution was added to each well after the supernatants were carefully discarded. The OD value of the product was evaluated using a microplate reader (Bio-Rad, Hercules, CA, USA) at a wavelength of 490 nm (n = 20). For the cell count assay [14,24], SCs were trypsinized and washed with PBS 3 times, and viable cells were counted using a hemocytometer under an automated cell counter (Count Star, Shanghai, China, n = 10).
