SP1 and lung carcinoma: PPP2R1B has been identified as a tumor suppressor in colorectal and lung cancer.28 Mutation or deletion of the PPP2R1B gene has been shown to occur in 15% of primary colon tumors, generating a truncated protein that is unable to bind to the catalytic subunit to assemble the PP2A holoenzyme.28 It has been reported that PPP2R1B expression is regulated by multiple transcriptional factors including Ets-1, SP1/SP3 and RXRα/β.