Lactate is abundant in rapidly dividing cells due to the requirement for elevated glucose catabolism to support proliferation1-6. However, it is not known whether accumulated lactate affects the proliferative state. Here, we deploy a systematic approach to determine lactate-dependent regulation of proteins across the human proteome. From these data, we elucidate a mechanism of cell cycle regulation whereby accumulated lactate remodels the anaphase promoting complex (APC/C). Remodeling of APC/C in this way is caused by direct inhibition of the SUMO protease SENP1 by lactate. We discover that accumulated lactate binds and inhibits SENP1 by forming a complex with zinc in the SENP1 active site. SENP1 inhibition by lactate stabilizes SUMOylation of two residues on APC4, which drives UBE2C binding to APC/C. This direct regulation of APC/C by lactate stimulates timed degradation of cell cycle proteins, and efficient mitotic exit in proliferative human cells. The above mechanism is initiated upon mitotic entry when lactate abundance reaches its apex. In this way, accumulation of lactate communicates the consequences of a nutrient replete growth phase to stimulate timed opening of APC/C, cell division, and proliferation. Conversely, persistent accumulation of lactate drives aberrant APC/C remodeling and can overcome anti-mitotic pharmacology via mitotic slippage. Taken together, we define a biochemical mechanism through which lactate directly regulates protein function to control cell cycle and proliferation.
