Reactivation of the dormant tumor suppressor BASP1

MYC is the abbreviation for a cellular protein representing a gene regulator. MYC is a molecular switch converting multiple incoming signals into the activation or suppression of numerous genes that are important for cell growth and metabolism. However, hyperactivation or mutation of MYC leads to abnormal cell growth thereby transforming normal cells into tumor cells. In fact, high MYC protein levels are present in most human tumors classifying MYC as major cancer driver. This is also accompanied by the dysregulation of many MYC-dependent genes. We have previously shown that one of these target genes, termed BASP1, is specifically downregulated by MYC. Moreover, we discovered that BASP1 is switched off in cancer cells because otherwise it would inhibit MYC-induced cell transformation. Reports from other research groups confirmed BASP1 suppression in several human tumors including breast cancer or leukemia. When BASP1 is delivered from outside into these cells, the tumor cells stop growing. Therefore, re-activation of the dormant BASP1 gene in human tumor cells may interfere in general with cancer cell growth and viability. Subsequent analyses of the growth-arrested cancer cells should identify potential new targets for compounds, which could be used as drugs to interfere with growth and viability of MYC-dependent tumor cells. In this project, several biochemical and cell biological approaches are applied. To understand why the BASP1 gene is downregulated in human cancer, the region which controls BASP1 expression is investigated in detail. In addition, regulatory mechanisms acting on the BASP1 protein product are investigated. The above mentioned re-activation of silenced BASP1 in human cancer cells is achieved by using a special application of the so-called CRISPR technology, which was originally developed for specific gene editing. The manipulated cells are then investigated to test if they have lost characteristic properties of cancer cells. Moreover, additional proteins that are involved in this tumor suppressive process are identified by a modern DNA sequencing technique termed ChIP-seq, and by mass spectrometry, a physical method to determine the mass and the identity of a protein. The results should deepen our knowledge about molecular mechanisms how aberrantly expressed MYC drives tumor formation in human cells. The developed procedures could be also transferred for testing other MYC-repressed targets with growth inhibiting functions. The elucidation of these principles has the potential to promote the design of novel MYC inhibitors for specific cancer therapy. Apart from the principal investigator and his team, the groups of Marcel Kwiatkowski, Ph.D. (Institute of Biochemistry, University of Innsbruck) for mass spectrometry analyses, and of Zoran Culig, M.D. (Department of Urology, Medical University of Innsbruck) for experimental cancer models, participate in this project.

The main point is that turning back on a normally silenced gene called BASP1 can switch off the cancer driving MYC program in colorectal cancer cells, making them behave less like tumors. Furthermore, a preclinical drug that blocks a related signal achieves a similar MYC shutdown, suggesting new ways to treat MYC dependent cancers. Colorectal cancer cells often rely on an overactive growth switch called MYC. In many of these cells, another gene termed BASP1 is kept silent. We asked a simple question: what happens if we restore BASP1? Using two approaches, either adding BASP1 directly or reactivating the cell's own BASP1 gene with a CRISPR based tool, we found that BASP1 powerfully counters the cancerous behavior of these cells. When BASP1 was restored, cells lost hallmark tumor traits. They stopped piling up when crowded thereby restoring contact inhibition, failed to grow without attachment, which is a key property of malignant cells, and formed far fewer tumors in preclinical tests. The cells also looked more like healthy, mature tissue under the microscope. At the molecular level, BASP1 reduced the amount of MYC protein by turning down the MYC gene itself. This occurred because BASP1 can interact with partners in a major growth pathway, the so-called WNT signaling pathway, and bind near the MYC gene to dampen its activity. We also discovered that BASP1 lowers the levels or activity of several parts of the WNT pathway, including a protein enzyme called TNIK. TNIK helps to switch on MYC through a factor called TCF7L2. When we treated colorectal cancer cells with a preclinical TNIK blocking drug, MYC levels fell and MYC could no longer team up with its usual partner MAX, and thus further weakening MYC's effects. Hence, these findings show two complementary ways to quiet MYC: restoring BASP1 or inhibiting TNIK. Why this matters: MYC drives growth in many human cancers, but directly blocking it with drugs has been difficult. Our work points to practical, upstream switches-BASP1 and TNIK-that can turn MYC down. Reactivating BASP1 (for example, with epigenetic therapies) or using TNIK inhibitors could reduce tumor growth and make cancers less aggressive, especially in tumors that depend on WNT signals to sustain MYC. These strategies could guide more personalized treatments by selecting patients with high MYC activity and low BASP1 expression. Beyond colorectal cancer, the BASP1-MYC link may be also relevant to other MYC driven tumors, although BASP1's role can vary by cancer type and will require careful validation. In short, restoring a natural brake (BASP1) and targeting a key helper (TNIK) offer promising, testable routes to tame MYC-a central engine of cancer growth-with potential medical and societal benefits if translated into safe, effective therapies.