CSB Special Seminar – Ridhdhi Desai, PhD – Harvard Medical School and Drexel University

CSB Special Seminar

Ridhdhi Desai, Ph.D.

Harvard Medical School and Drexel University

TITLE: Stem-cell Derived Organoids to Model and Dissect Mechanisms of Pancreatic Diseases

ABSTRACT:

Like other epithelial malignancies, pancreatic ductal adenocarcinoma (PDAC) arises from noninvasive precancerous lesions. PDAC is thought to develop within the ductal compartment of exocrine component and is associated with two major types of asymptomatic precancerous lesions – microscopic pancreatic intraepithelial neoplasia (PanINs) and macroscopic mucin-producing cystic neoplasms, namely, intraductal papillary mucinous neoplasms (IPMN). Unlike PanINs, which currently remain clinically undetectable, IPMNs form large cystic mucin-producing neoplasms and can be clinically diagnosed. Comprehensive genomic analyses indicate that activating mutations in oncogenes GNAS(R201C) and KRAS(G12V) are associated with IPMN pathogenesis. Specifically, activating mutations in GNAS, which encodes for the alpha subunit of a G-protein, are found exclusively in 66% of IPMN lesions. Although genetically engineered mouse models (GEMMs) have provided some insights into the function of GNAS in the initiation of IPMN, the biological mechanisms by which oncogenic GNAS affects IPMN development within the exocrine pancreas are limited, largely due to challenges in maintaining human acinar and ductal cells in culture.

To address this limitation, we have developed a human pancreatic ductal and acini organoid model system from embryonic and pluripotent stem cells to investigate mechanisms regulating GNAS^R201C-induced IPMNs. Using this strategy, we show that expression of GNAS^R201C in human ductal organoids recapitulates many features of IPMN including lumen expansion and mucin secretion. Surprisingly, expression of GNAS^R201Calso induces aberrant cell proliferation in a PKA-signaling independent manner in short-term and stable, long-term cultures of ductal organoids. By contrast, GNAS^R201C-expression in acinar organoids results in limited phenotypic changes and PKA signaling-dependent increase in cell proliferation. We also show that co-expression of oncogenic KRAS^G12V and GNAS^R201C retained PKA-independence in ductal organoids and PKA-dependence in acinar organoids for stimulation of cell proliferation. Delving into the mechanism, BioID-based proteomic and RNA-seq-based genomic approaches reveal an intriguing possibility that oncogenic GNAS interacts with proteins involved in the ubiquitin proteosome system to regulate PI3K-AKT and PPAR signaling pathways. Altogether, we establish a platform to investigate mechanisms by which oncogenic GNAS promotes PKA-independent proliferation and demonstrate the utility of stem cell-derived pancreatic organoid model for investigating cell lineage-specific mechanisms in the initiation and progression of pancreatic cancer.

HOST: Ulrich Tepass

LOCATION: Cell and Systems Biology, 25 Harbord Street, Suite 432

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