MAT1A and neoplasm: Meanwhile, the switch expression of MAT1A/MAT2A, accompanied with a decrease of SAM acting on tumor suppressor, is occurred in HCC, which has been attributed to that catalytic activity of MAT1A is higher than that of MAT2A and SAM plays a function of tumor suppression.31,43 On the contrary, our study found that MAT2A knockdown decreased methionine cycle.