Significance The DLC1 tumor suppressor gene is commonly lost in cancer by genomic deletion or epigenetic silencing, leading to loss of gene transcription. DLC1 encodes a GTPase-activating protein for the RhoA small GTPase, and DLC1 loss of expression results in aberrant RhoA activation and signaling. Unexpectedly, we found that a subset of non-small cell lung cancer patient tumors and cell lines retained DLC1 mRNA but not protein expression. We determined that the CUL4A–DDB1–FBXW5 E3 ubiquitin ligase complex is responsible for loss of DLC1 protein expression. Suppression of FBXW5 function restored DLC1-dependent lung cancer cell growth suppression. Our observations identify a mechanism for posttranslational loss of DLC1 function in cancer and substrate for CRL4A-FBXW5–driven cancer growth.