Genomic and phenotypic analysis reveals a key role for CCN1 (CYR61) in BAG3-modulated adhesion and invasion

Chaperone protein quantity may regulate the balance of proteins involved in invasion and malignancy. BAG3 is a co-chaperone and pro-survival protein that has been implicated in adhesion, migration, and metastasis. We reported that BAG3 overexpression in MDA435 human breast cancer cells results in a significant decrease in migration and adhesion to matrix molecules that is reversed upon deletion of the BAG3 proline-rich domain (dPXXP). We now hypothesize that transcriptional analysis would identify proteins involved in matrix-related processes that are regulated by BAG3 and/or its PXXP domain mutant. Expression array analysis of MDA435 cells overexpressing either wild-type BAG3 (FL) or dPXXP identified CCN1 as a BAG3 target protein. CCN1 is a known AP-1 target. Increased AP-1 transcriptional activity and AP-1 DNA-binding was found in MDA435 dPXXP cells. Consistent with these findings, CCN1 quantity and secretion were increased in dPXXP mutants but suppressed in FL cells; both BAG3 forms resulted in up-regulated CCN1 in HeLa cells. CCN1 silencing in the BAG3 FL overexpressors reduced the already low phospho-integrin beta 1 in response to attachment on collagen IV. Matrigel invasion of HeLa cells engineered with the BAG3 constructs was enhanced in FL cells and minimal in dPXXP cells. CCN1 silencing blocked a greater percentage of the serum-induced invasion in FL cells than in dPXXP cells. This implies a context-dependent function of BAG3 oil CCN1 and thus mesenchymal behaviour. CCN1 may be necessary for adhesion and matrix-related signalling in FL cells, abrogating a negative signal of the PXXP domain when BAG3 is intact. We propose that BAG3 regulates CCN1 expression to regulate tumour cell adhesion Published in 2009 by John Wiley & Sons, Ltd.