Dual Roles for Coactivator Activator and its Counterbalancing Isoform Coactivator Modulator in Human Kidney Cell Tumorigenesis

Abstract

Coactivator activator (CoAA) has been reported to be a coactivator that regulates steroid receptor-mediated transcription and alternative RNA splicing. Herein, we show that CoAA is a dual-function coregulator that inhibits G 1 -S transition in human kidney cells and suppresses anchorageindependent growth and xenograft tumor formation. Suppression occurs in part by down-regulating c-myc and its downstream effectors ccnd1 and skp2 and causing accumulation of p27/Kip1 protein. In this cellular setting, CoAA directly represses the proto-oncogene c-myc by recruiting HDAC3 protein and decreasing both the acetylation of histone H3 and the presence of RNA polymerase II on the c-myc promoter. Interestingly, a splicing isoform of CoAA, coactivator modulator (CoAM), antagonizes CoAA-induced G 1 -S transition and growth inhibition by negatively regulating the mRNA levels of the endogenous CoAA isoform. In addition, we found that expression of CoAA protein is significantly decreased in human renal cell carcinoma compared with normal kidney. Our study presents evidence that CoAA is a potential tumor suppressor in renal carcinoma and that CoAM is a counterbalancing splice isoform. This is, thus far, the only example of a nuclear receptor coregulator involved in suppression of kidney cancer and suggests potentially significant new roles for coregulators in renal cancer biology. [Cancer Res 2008;68(19):7887-96]

E2/Estrogen Receptor/Sjogren Syndrome-Associated Autoantigen Relieves Coactivator Activator-Induced G1/S Arrest To Promote Breast Tumorigenicity

“…Based on our previous report showing that CoAA directly represses MYC gene expression (16), we speculated that SSA could activate MYC by removing CoAA-mediated repression. To test this, we took advantage of the 293-CoAA cells, generated by us previously, in which CoAA protein could be induced upon treatment with tetracycline (16). Similar to our previous finding (16), the expression of the MYC gene was reduced upon induction of CoAA by tetracycline (Fig.…”

“…Although a previous study suggested that mRNA levels of CoAA were upregulated in several cancer cell lines (17), a significant population of cancer tissues exhibit smaller amounts of CoAA protein than normal tissues (see Table S1 in the supplemental material), supporting our previous findings of the tumor-suppressive activity of CoAA (16). Among these cancers, we chose to examine two cell lines, MCF7 and Ishikawa, representing breast cancer and endometrial cancer, respectively.…”

“…Bound DNA eluted from immunoprecipitates was analyzed by quantitative PCR normalized by an IgG control, and results are presented as the relative fold enrichment over input. Quantitative reverse transcription-PCR (RT-PCR) analysis of endogenous MYC and TFF1/pS2 mRNA was performed as described before (16). To avoid variations from different samples, the relative mRNA level of each gene was normalized against the 36B4 mRNA content of the same sample.…”

“…In an effort to identify CoAA-interacting proteins that regulate CoAA protein stability, we isolated CoAA-interacting proteins by affinity purification with M2 agarose using extracts prepared from 293-vector or 293-CoAA cells that stably express either control vector or CoAA, respectively (16). Subsequent to incubation with each cell extract, bound proteins were eluted from extensively washed M2 agarose beads and analyzed by SDS-PAGE and Coomassie staining (22).…”

“…Our laboratory and other laboratories have reported that coactivator activator (CoAA; gene symbol RBM14) plays a yin-yang function in oncogenesis (16,17). CoAA was originally reported as a protein interacting with the proto-oncogene for synovial sarcoma translocation (SYT) protein (18), suggesting its potential implication in tumorigenesis.…”