Joelle Sacks Suarez

BAP1 and HMGB1 alterations are implicated in the pathogenesis of mesothelioma, an aggressive cancer of the membranes covering the thoracic and abdominal cavities. Genetic inactivating mutations of BAP1 cause cancer in ~100% of carriers. The mechanism/s that regulate BAP1 expression were unknown. We discovered that HMGB1 directly modulates BAP1 expression. Studying our Hmgb1 knock-out mouse mesothelioma models, primary fibroblasts obtained from carriers of pathogenic heterozygous germline BAP1 mutations, and mesothelioma cell lines, we discovered that HMGB1 loss caused a significant reduction in BAP1 expression and protein levels, whereas HMGB1 overexpression increased BAP1 mRNA and protein levels. We demonstrated that HMGB1 binds to the BAP1 promoter and activates its transcription, leading to BAP1 overexpression, which in turn promoted the proliferation, migration, and invasion of mesothelioma cells. These findings were confirmed in lung, colon, and cholangiocarcinoma cell lines. These findings indicate that while BAP1 inactivating mutations promote cancer development, cancer cells that do not express BAP1 are less aggressive, pointing to the HMGB1-BAP1 axis as a novel attractive target for therapy. Furthermore, our discovery that HMGB1-driven BAP1 overexpression supports cancer growth provides a mechanistic rationale for the improved survival observed in mesothelioma patients with somatic BAP1 inactivating mutations.

Background: Intracellular miRNA transfer is an intriguing and lesser-described mode of intracellular communication. Epithelial ovarian carcinoma, of which the high-grade serous histotype represents the most common and deadliest form, is characterized by a microenvironment consisting of tumor and stromal cells, ascitic fluid, and extracellular matrix, presenting a rich milieu of factors that can affect neighboring cells. Methods: We examined the mode of miR transfer in serous ovarian carcinoma cell lines cultured on different extracellular matrix supports both in two-dimensional and three-dimensional formats coupled with traditional, live-cell time-lapse, multiphoton fluorescence imaging modalities, and fluorescence-activated cell sorting approaches. Results: Our data demonstrate that miR can transfer between cells both in culture and in vivo. Moreover, transferred miRNA results in target-specific gene expression changes in recipient cells. Our data indicate that miR transfer occurs via extracellular vesicles, which shuttle from and within the donor and recipient cells via endocytic pathways recruiting sorting, early, late, and recycling endosomes. Conclusions: Our study highlights the phenomenon of miR transfer as a mode of communication between serous ovarian cancer cells, which can affect both treatment and diagnostics of this disease.

We report that ~1.8% of all mesothelioma patients and 4.9% of those younger than 55, carry rare germline variants of the BRCA1 associated RING domain 1 ( BARD1) gene that were predicted to be damaging by computational analyses. We conducted functional assays, essential for accurate interpretation of missense variants, in primary fibroblasts that we established in tissue culture from a patient carrying the heterozygous BARD1 ^V523A mutation. We found that these cells had genomic instability, reduced DNA repair, and impaired apoptosis. Investigating the underlying signaling pathways, we found that BARD1 forms a trimeric protein complex with p53 and SERCA2 that regulates calcium signaling and apoptosis. We validated these findings in BARD1 -silenced primary human mesothelial cells exposed to asbestos. Our study elucidated mechanisms of BARD1 activity and revealed that heterozygous germline BARD1 mutations favor the development of mesothelioma and increase the susceptibility to asbestos carcinogenesis. These mesotheliomas are significantly less aggressive compared to mesotheliomas in asbestos workers.

Disseminating epithelial ovarian cancer cells often become assembled into spheroids prior to their arrival at metastatic sites within the peritoneal cavity. Although epithelial ovarian carcinoma (EOC) is the deadliest gynecologic malignancy, the mechanisms regulating formation and metastatic potential of spheroids are poorly understood. We show that expression of a cell surface glycoprotein CD44 is an important contributing factor for spheroid formation and spheroid adhesion to mesothelial cells, and its loss impairs mesenteric metastasis. In contrast, loss of CD44 resulted in significant increase of tumor burden at several locoregional sites, including liver, and unleashed distant metastases to the thoracic cavity. Altogether our studies suggest that CD44 regulates metastatic progression of EOC in an organ-specific manner.Implications:Expression of CD44 promotes spheroid formation, mesothelial adhesion, and formation of mesenteric metastasis, but it suppresses development of metastasis to several peritoneal sites, including liver, and the thoracic cavity.

Disseminating epithelial ovarian cancer cells often become assembled into spheroids prior to their arrival at metastatic sites within the peritoneal cavity. Although epithelial ovarian carcinoma (EOC) is the deadliest gynecologic malignancy, the mechanisms regulating formation and metastatic potential of spheroids are poorly understood. We show that expression of a cell surface glycoprotein CD44 is an important contributing factor for spheroid formation and spheroid adhesion to mesothelial cells, and its loss impairs mesenteric metastasis. In contrast, loss of CD44 resulted in significant increase of tumor burden at several locoregional sites, including liver, and unleashed distant metastases to the thoracic cavity. Altogether our studies suggest that CD44 regulates metastatic progression of EOC in an organ-specific manner.Implications:Expression of CD44 promotes spheroid formation, mesothelial adhesion, and formation of mesenteric metastasis, but it suppresses development of metastasis to several peritoneal sites, including liver, and the thoracic cavity.

SUPPLEMENTARY FIGURE 9. The parental and CD44-/- ES2 cells colonize intra- and retroperitoneal sites with different efficiency.