Abstract B12: Yes-Associated Protein: A master metabolic regulator In medulloblastoma
Authors: Malhotra Anshu , Dey Abhinav , Kenney Anna Marie 
Published: May 2016

Downstream of mitogenic Sonic hedgehog (Shh) signaling, Yes-Associated Protein (YAP) can drive proliferation in Cerebellar Granule Neural Progenitor (CGNP) cells. CGNPs are the proposed cells of origin of SHH medulloblastomas. They are a neural progenitor type whose developmental expansion requires signaling by Shh, a secreted ligand produced by the neighboring Purkinje neurons. Approximately 30% of human medulloblastomas bear an activated Sonic hedgehog pathway gene expression signature. Ectopic expression of YAP promotes highly aggressive Shh-driven medulloblastoma growth and radio-resistance (Fernandez et al., 2009). Medulloblastoma being the most common solid malignancy of childhood and a leading cause of pediatric mortality, the current standard of care results in about 60% “cure” rate. But the survivors are beset with long-term side effects, including cognitive impairment, seizures, premature aging, and susceptibility to cancer. Moreover, recurrence and metastasis are lethal. Therefore, identification of novel modes of molecular targeted therapies is critical for the improved quality of life for survivors and reduced incidence of recurrence and metastasis.

Recently, there has been renewed interest in how altered metabolic patterns in tumors could be exploited for therapeutic purposes. Deregulating the metabolic machinery for aberrant energy utilization is one of the hallmarks of a proliferating cancer cell. Previously, our lab made the novel observation that Shh mitogenic/oncogenic signaling is tightly coupled to the reprogramming of mitochondrial bioenergetics: Shh inhibits fatty acid oxidation (FAO, or β-oxidation) while driving increased fatty acid synthesis (FAS), an early step of lipogenesis. The production of citrate, an essential component for fatty acid synthesis, occurs inside the mitochondrion via the Tri-carboxylic acid cycle (TCA).

We analyzed the effect of Shh treatment and ectopic YAP expression on CGNPs and found that YAP increases levels of fatty acid synthase (FASN) and ATP citrate lyase (ACLY), while YAP knock-down in Shh-treated CGNPs resulted in reduced levels of these enzymes. Moreover, we also observed a surprising decrease in mitochondrial membrane potential. This prompted us to further analyze the ultrastructure of mitochondria using Transmission Electron Microscopy. Shh-treated or ectopic YAP-expressing mitochondria presented a swollen morphology, along with an expanded matrix space and deformed cristae structure, typical of morphologically aberrant mitochondria. These differences in mitochondrial structure were also visible in ultrastructures of SmoA1 tumor tissue as well as in vitro cultures of SmoA1 tumor cells (MBCs). Being dynamic structures, mitochondria undergo constant fusion and fission events, which contribute to their biogenesis. Expression of fusion genes Mitofusin 1 and 2 was reduced while DRP1, a fission promoting gene was highly induced in all samples under study. Ectopic expression of Mitofusin 1 and 2, and knock down of DRP1 in CGNPs and MBCs not only restores the membrane potential to the non-proliferating state, but also indicates a reduction in proliferation.

Our study thus implicates YAP-regulated metabolic pathways and enzymes as potential targets for novel medulloblastoma therapies. Our goal is to determine whether hampering YAP-mediated mitochondrial fragmentation can restore the metabolic profile of tumor cells to that of non-transformed, non-proliferating cells, thus suggesting a potential novel treatment paradigm that may reduce or eliminate the requirement for high dose radiation.

Citation Format: Anshu Malhotra, Abhinav Dey, Anna Marie Kenney. Yes-Associated Protein: A master metabolic regulator In medulloblastoma. [abstract]. In: Proceedings of the AACR Special Conference: Metabolism and Cancer; Jun 7-10, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(1_Suppl):Abstract nr B12.