Abstract 292: Cell non-autonomous downregulation of the tumor suppressor DAB2IP in the cancer microenvironment: Molecular mechanism and biological implications
Authors: Bellazzo Arianna , De Florian Fania Rossella , Agostinis Chiara , Bulla Roberta , Segatto Ilenia , Belletti Barbara , D’Agostino Vito G. , Bonapace Ian M. , Collavin Licio 
Published: March 2024

Abstract
Background and Purpose: The tumor suppressor DAB2IP is a cytoplasmic Ras-GAP and an adaptor protein that restrains oncogenic signaling by extracellular inputs, contributing to modulate the dynamic crosstalk established between tumor cells and their stromal compartment. In human malignancies, DAB2IP is frequently disabled by epigenetic and post-transcriptional means. DAB2IP loss-of-function in cancer cells promotes their aberrant proliferation, dissemination, and tumor-promoting inflammation, potentially favor progression of tumors. Intriguingly, endothelial-specific DAB2IP depletion in mouse models fosters the formation of a pro-metastatic niche, implicating that also the loss-of-function of DAB2IP in stromal cells might dramatically impact cancer progression. We previously found that the secretome of prostate cancer cells reduced DAB2IP levels in non-transformed prostate epithelial cell lines, and in primary endothelial cells, thereby fostering their proliferation, migration and expression of angiogenesis markers. Accordingly, cell non-autonomous DAB2IP inactivation in the stromal compartment may reprogram the response to paracrine and autocrine signals, thus supporting a tumor-promoting behavior; however, molecular basis and clinical implication of this phenomenon await clarification. Materials and
Methods: We used conditioned medium (CM) from prostate (PCa) and breast (BCa) cancer cell lines, to study its effects in mediating DAB2IP downregulation and in inducing tumor-associated phenotypes in endothelial cell and fibroblasts. Through multiple approaches, we isolated extracellular vesicles from PCa and BCa conditioned media, to test their involvement in mediating DAB2IP downregulation in recipient cells. Finally, we used cancer cells’CM or specific siRNAs to study the consequence of DAB2IP loss in fibroblasts.
Results: The treatment with CM from PCa and BCa cells induces DAB2IP downregulation in immortalized and in primary fibroblasts, and in endothelial cells. Analysis of DAB2IP levels in primary fibroblasts from PCa and BCa surgical samples confirmed differential expression of DAB2IP protein in normal vs. tumor-associated fibroblasts. Exploring the biochemical nature of extracellular signals involved in DAB2IP downregulation by cancer cells’ CM, we found that DAB2IP inhibition in recipient cells is partially mediated by miR-149-3p contained in extracellular vesicles. Finally, we found that DAB2IP reduction potentiates fibroblasts proliferation and invasion, facilitates gel contraction and extracellular matrix remodeling, and fosters expression of markers of activated fibroblasts.
Conclusions: Together, these data support the hypothesis that cancer cells can modulate DAB2IP levels in nearby stromal cells, pushing them to acquire a metastasis-supporting phenotypes.
Citation Format: Arianna Bellazzo, Rossella De Florian Fania, Chiara Agostinis, Roberta Bulla, Ilenia Segatto, Barbara Belletti, Vito G. D’Agostino, Ian M. Bonapace, Licio Collavin. Cell non-autonomous downregulation of the tumor suppressor DAB2IP in the cancer microenvironment: Molecular mechanism and biological implications [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 292.