Reactivation of the silenced BASP1 gene suppresses oncogenic WNT signaling in human colorectal cancer cells

TL;DR

Reactivating the BASP1 gene in colorectal cancer cells suppresses harmful WNT and MYC signaling, reducing tumor growth and promoting normal cell behavior.

Contribution

Demonstrates that reactivating the silenced BASP1 gene can suppress oncogenic WNT and MYC signaling in colorectal cancer cells.

Findings

BASP1 reactivation leads to repression of WNT signaling and downregulation of MYC in colorectal cancer cells.

BASP1 interacts with β-catenin and binds to the MYC promoter to suppress its expression.

Inhibiting TNIK, a WNT-associated kinase, also represses MYC, offering new therapeutic strategies.

Abstract

Due to its pleiotropic functions in gene regulation, chromatin remodeling, and metabolism, MYC family members have a fundamental impact on cell growth control and proliferation. Aberrant activation of MYC provokes derailed cell signaling and malignant cell transformation in most human tumors. Therefore, genetic or pharmacological MYC inhibition represents a rational therapeutic approach. We have achieved this in colorectal cancer cells by genetically inducing transcriptional activation of BASP1 whose protein product interferes with MYC activity. This leads to suppression of tumor formation accompanied by WNT signaling repression and transcriptional downregulation of the effector target MYC. Furthermore, blocking WNT-associated protein kinase TNIK using a small molecule also results in transcriptional MYC repression, thereby expanding the tool repertoire to inhibit this oncogenic transcription factor.

Starting from human colon cancer cells showing aberrant WNT/β-catenin/TCF signaling, hyperactivated MYC, and silenced BASP1, we generated stable cell lines overexpressing BASP1, either ectopically, or by reactivating the dormant BASP1 promoter using a lentiviral CRISPR-based system. BASP1 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 MYC downregulation involving BASP1 interaction with β-catenin and binding to the MYC promoter. Upon BASP1 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 MYC 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.

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