Cyr61 suppresses the growth of non-small-cell lung cancer cells via the β-catenin–c-myc–p53 pathway

Cysteine-rich protein 61 (Cyr61) is a growth factor-inducible, immediate-early gene that has multifaceted activities in various cancers. In a previous study, we found that Cyr61 inhibited the growth of the H520 and H460 non-small-cell lung cancer (NSCLC) cell lines. In further studies, we now report that p53 plays a pivotal role in Cyr61-dependent cellular growth arrest. Blocking Cyr61 with a Cyr61 antibody resulted in the downregulation of expression of p53 and p21, as well as partially reversing the growth suppression of H520-Cyr61 cells. Proliferation of NSCLC cell lines (NCI-H157, H125, H1299), having a mutant p53, were not suppressed by Cyr61. Inhibition of wild-type p53, by either human papilloma virus type 16 E6 or a dominant-negative p53, resulted in the rescue of the growth suppression mediated by Cyr61 in the H520-Cyr61 cells. The enhanced levels of p21 WAF1 and p130/RB2, in the Cyr61-expressing H520-Cyr61 cells, were also inhibited by blocking p53 showing that p21 and p130 were induced by p53 in these cells. In addition, levels of both c- myc and β -catenin increased in Cyr61 stably transfected H520 cells. Moreover, β -catenin was translocated into the nucleus in these cells. Inhibition of c- myc expression in the H520-Cyr61 cells with antisense c- myc resulted in their decreased levels of p53. Transfecting cells with a dominant-negative T-cell factor (TCF4), the specific inhibitor of the β -catenin/TCF4 complex, downregulated the expression of c- myc . Taken together, the data suggest that Cyr61 suppressed the growth of NSCLC cells by triggering a signal transduction pathway through β -catenin. In this pathway, Cyr61 activated the β -catenin/TCF4 complex, which promoted the expression of c- myc and the latter induced expression of p53, and p53 upregulated p21 WAF1 and p130/RB2, resulting in growth arrest.