Tumor-suppressor function of Beclin 1 in breast cancer cells requires E-cadherin.

Abstract

Beclin 1, an autophagy and haploinsufficient tumor-suppressor protein, is frequently monoallelically deleted in breast and ovarian cancers. However, the precise mechanisms by which Beclin 1 inhibits tumor growth remain largely unknown. To address this question, we performed a genome-wide CRISPR/Cas9 screen in MCF7 breast cancer cells to identify genes whose loss of function reverse Beclin 1-dependent inhibition of cellular proliferation. Small guide RNAs targeting <i>CDH1</i> and <i>CTNNA1</i>, tumor-suppressor genes that encode cadherin/catenin complex members E-cadherin and alpha-catenin, respectively, were highly enriched in the screen. CRISPR/Cas9-mediated knockout of <i>CDH1</i> or <i>CTNNA1</i> reversed Beclin 1-dependent suppression of breast cancer cell proliferation and anchorage-independent growth. Moreover, deletion of <i>CDH1</i> or <i>CTNNA1</i> inhibited the tumor-suppressor effects of Beclin 1 in breast cancer xenografts. Enforced Beclin 1 expression in MCF7 cells and tumor xenografts increased cell surface localization of E-cadherin and decreased expression of mesenchymal markers and beta-catenin/Wnt target genes. Furthermore, CRISPR/Cas9-mediated knockout of <i>BECN1</i> and the autophagy class III phosphatidylinositol kinase complex 2 (PI3KC3-C2) gene, <i>UVRAG</i>, but not PI3KC3-C1-specific <i>ATG14</i> or other autophagy genes <i>ATG13</i>, <i>ATG5</i>, or <i>ATG7</i>, resulted in decreased E-cadherin plasma membrane and increased cytoplasmic E-cadherin localization. Taken together, these data reveal previously unrecognized cooperation between Beclin 1 and E-cadherin-mediated tumor suppression in breast cancer cells.