Reactivation of the silenced <i>BASP1</i> gene suppresses oncogenic WNT signaling in human colorectal cancer cells

Starting from human colon cancer cells showing aberrant WNT/β-catenin/TCF signaling, hyperactivated <i>MYC,</i> and silenced <i>BASP1</i>, we generated stable cell lines overexpressing <i>BASP1</i>, either ectopically, or by reactivating the dormant <i>BASP1</i> promoter using a lentiviral CRISPR-based system. <i>BASP1</i> encodes a neuronal signaling protein and transcriptional corepressor, from which tumor-suppressive functions have been described in avian cell systems and in multiple human cancer cell types. Proteome and transcriptome analyses revealed activation of several tumor and metastasis suppressors in BASP1-expressing cells, which also show strong repression of the transformed phenotype in terms of contact inhibition, anchorage-independent growth, and tumor formation. Cells with reactivated BASP1 display a flat and differentiated morphology with enhanced migratory potential, accompanied by expression of multiple genes implicated in actin polymerization, focal adhesion, and neuronal migration. Furthermore, MYC protein expression is substantially repressed due to BASP1-mediated transcriptional <i>MYC</i> downregulation involving BASP1 interaction with β-catenin and binding to the <i>MYC</i> promoter. Upon <i>BASP1</i> activation, multiple key proteins of the canonical WNT signaling pathway become suppressed. One of these BASP1 targets is the protein kinase TNIK catalyzing phosphorylation of TCF7L2, the latter required for transcriptional <i>MYC</i> activation. Results obtained with a preclinical TNIK inhibitor in human colorectal cancer cells show efficient abrogation of MYC expression and consequently impaired dimerization with its interaction partner MAX. The antagonistic BASP1 effect on MYC and the MYC dependency on TNIK could enhance the development of strategies to interfere with oncogenic functions of the cancer driver MYC.