Activation of oncogene in normal cells causes cell proliferation arrest, termed oncogene-induced senescence (OIS), which acts as a critical brake for malignant transformation. Investigating how OIS is maintained in non-transformed cells and how it is overcome during transformation will not only reveal the mechanisms of oncogenesis but also identify therapeutic vulnerabilities for cancer treatment. Despite cell proliferation arrest, the senescent cells remain metabolically active. These metabolic alterations contribute to OIS establishment and maintenance, and interfering metabolic reprogramming may cause senescence-bypass or escape and promote tumorigenesis. We have demonstrated that hyperactivation of PI3K/AKT/mTORC1 pathway in normal cells induces senescence, referred to as AKT-induced senescence (AIS). From a high throughput genomic screen in human fibroblasts expressing activated AKT, we identified a panel of metabolism-associated genes as the potential key regulators of AIS. Particularly cysteine metabolism pathway is implicated to play a critical role in maintenance of AIS-associated cell proliferation arrest. We further demonstrated that depletion of CBS (cystathionine-beta-synthase), a key enzyme catalyzing the conversion of homocysteine and serine to cystathionine and involving in H2S and glutathione formation, caused AIS escape, which is associated with homocysteine accumulation. Moreover, loss of CBS expression was detected in a panel of human gastric cancer cell lines and overexpression of CBS reduced gastric tumor growth both in vitro and in vivo. Further exploring the functional role of CBS in AIS and tumorigenesis will provide more mechanistic insights into how metabolic reprogramming drive AIS and tumorigenesis.