STEM-07. IDENTIFICATION OF A NOVEL CSC SIGNALING AXIS CONTAINING JAM-A/SERPINB3/TGF-BETA

Abstract

Abstract Despite therapeutic interventions including surgery, radiation, and chemotherapy, multiple clones of treatment resistant cells repopulate the tumor, resulting in recurrence and a high rate of mortality in glioblastoma. Effective targeting of these cancer stem cells (CSCs) has been limited by our incomplete understanding of the intracellular signaling mechanisms maintaining the CSC state. Our laboratory previously identified junctional adhesion molecule-A (JAM-A) on CSCs and, through functional studies, demonstrated that JAM-A is both necessary and sufficient for self-renewal and tumor growth. We determined that JAM-A signals via Akt in GBM CSCs to sustain pluripotency transcription factor activity; however, the intermediate signaling network is yet to be fully elucidated. Therefore, our goal was to delineate the pathway downstream of JAM-A. To achieve this, we immunoprecipitated JAM-A from GBM CSCs and performed mass spectrometry leading to the identification of the serine/cysteine protease inhibitor SerpinB3. While SerpinB3 has a functional role in lung adenocarcinoma, breast, pancreas, as well as in hepatocellular carcinoma, there is limited information in GBM or CSCs, and its relationship to JAM-A is yet to be elucidated. Using in vitro CSC functional assays, we observed that SerpinB3 is necessary for the maintenance of CSCs. Additionally, in an intracranial implantation model of GBM the knockdown of SerpinB3 extended the survival of mice. Knockdown of SerpinB3 in multiple GBM CSCs models also led to decreased expression of TGF-β, a known regulator of the CSC state. We also observed that SerpinB3 stabilizes JAM-A expression and further studies are investigating the mechanism of this stabilization, identifying the specific interaction sites of JAM-A and Serpin B3, and determining how TGF-β alters the association through positive and negative feedback mechanisms. Taken together, these data highlight the role of SerpinB3 in GBM CSCs and provides a novel target to inhibit the JAM-A-mediated CSC maintenance as a next-generation GBM therapy.