PTEN, a widely investigated tumor suppressor, has at least two longer translational variants, PTEN and . However, the regulation and precise roles of endogenous PTEN/ in tumorigenesis remain greatly unknown. Here we show that USP9X and FBXW11 selectively regulate the stability of PTEN/ but not PTEN proteins by deubiqitination and ubiquitination respectively. USP9X promotes and FBXW11 suppresses tumorigenesis mediated by PTEN/. In contrast to the current paradigm for PTEN as a tumor suppressor, PTEN/ promote tumorigenesis of cancer cells in a phosphatase-independent manner. Mechanistically, PTEN/ localized in the nucleus regulate expressions of tumor-promoting genes such as NOTCH3 in the similar way as the H3K4 presenter WDR5. Further, PTEN/ but not PTEN directly interact with WDR5 to promote trimethylation of H3K4 and maintain a tumor-promoting signature. Taken together, our results indicate that PTEN/ are a double-edged sword for carcinogenesis, suggesting that reinterpretation of the importance of PTEN gene in carcinogenesis is warranted.