Oncogenic ASPP2 kappa exerts a regulatory role within the tumor microenvironment and promotes metastasis in TNBC models

Breast Cancer is the most common cancer in woman to date. While cure rates in localized stages are relatively good, tumor-associated death rates increase dramatically in the distant metastatic stage. Composition of the tumor microenvironment plays a decisive role therein. Metastasis is a complex, multistep process involving a multitude of intracellular steps of transformation, as well as interactions of tumor cells with the surrounding environment. The mechanisms underlying these processes are only partially understood. We have evidence that ASPP2 κ , a novel, oncogenic isoform of the p53-related tumor suppressor ASPP2, is involved in this process. ASPP2 κ is highly expressed in breast cancer and characterized by loss of the p53- as well as BCL-2 and NFκB-binding sites, impairing major pathways controlling cellular fate. We have demonstrated, that ASPP2 κ promotes a more aggressive tumor biology and shorter patient survival. We now show that ASPP2 k exerts a pro-tumorigenic role within the tumor microenvironment, facilitating neo-angiogenesis and early metastasis. To study the role of ASPP2 κ in a tissue context, we established a TNBC ASPP2 κ knock-down (KD) NOD/SCID as well as an immunocompetent BALB/C orthotopic ASPP2k knock-in mouse model, employing the human TNBC MDA-MB-231 and the murine 4T1 cell lines. ASPP2 k KD and KI primary and metastatic lesions, as well as the respective controls, were explanted and analyzed on the transcriptional and translational level. Proteome arrays and bulk RNA sequencing was performed on TNBC cell models. Results were confirmed by qPCR, WB, FACS and ELISA assays. All conducted analyses confirme a driving role of ASPP2 k in angiogenesis and early metastasis as well as a tumor promoting role in the microenvironment. Comprehensive analyses of our bulk RNA sequencing data identified significant differential expression patterns of genes clustered within the GO terms “angiogenesis”, “EMT” and “immune response” (149/200 genes within GO:0001525 angiogenesis, 33/43 genes associated with GO:0001837 EMT and 134/194 genes linked to the GO:0006955 Immune Response). Pathways involved in metastasis, angiogenesis and pro-inflammatory signaling were studied in detail in dependency of ASPP2 κ expression. ELISA readouts confirmed secretion of pro-angiogenic growth factors (eg. VEGF, Angiogenin or PDGF) in dependency of ASPP2 κ expression (KD cells: VEGF 247.2 ± 97.8 pg/mL vs. 535.9 ± 60.8 pg/mL in controls). TNBC tumoroid models confirme inhibition of invasive growth in ASPP2 κ attenuated models. Differences in vascularization were confirmed by immunohistochemistry and confocal microscopy. We here demonstrate, that ASPP2 κ exerts a regulatory role on key hallmarks of metastasis and the tumor microenvironment, promoting tumor progression and metastasis. Therapeutic inhibition of ASPP2 κ might provide a completely new approach to combat metastasis in the future.