The Family with sequence similarity 129 (FAM129) contains three membrane proteins, FAM129A, B and C. FAM129A (also called Niban) and FAM129C (also called BCNP1) have been found to be up-regulated in thyroid tumors and chronic lymphocytic leukemia, respectively. Although phosphorylation of FAM129B has been suggested to play a role in controlling melanoma cell invasion, the molecular mechanism of FAM129B in tumorigenesis remains largely unknown. In this study, we first identified FAM129B as one of proteins with altered phosphorylation status in breast cancer stem cells by the phosphor-mass spectrum technique. Silencing of FAM129B expression in breast cancer cell line, MDA-MB-231, led to decreased proliferation, along with flattened and rounded cell morphology. By mammalian two-hybrid system and FRET (fluorescence resonance energy transfer) assay, KEAP1 (kelch-like ECH-associated protein 1) was detected to interact with FAM129B. KEAP1 has been reported to function as a substrate adaptor protein for Cul3-dependent E3 ligase complex to repress IKKβ and transcription factor Nrf2. We indeed observed that the expression of NF-κB and Nrf2 downstream genes, FN1 and NQO1, was down-regulated in FAM129B-silenced cells by qPCR analysis. On the other hand, FAM129B together with either IKKβ or Nrf2 synergistically activated NF-κB and Nrf2 promoter activity by reporter assays. Taken together, our results suggest that FAM129B might play an important role in the regulation of cell proliferation in cancers by inactivating KEAP1 which in turn activates Nrf2 and IKKβ activities.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1947. doi:10.1158/1538-7445.AM2011-1947