Abstract 2736: Genetic deletion of the prkar1a in the endocrine pancreas promotes neuroendocrine carcinogenesis.
Authors: Saloustros Emmanouil , Tsokos Maria , Salpea Paraskevi , Starost Matthew , Liu Sisi , Guang Li , Nesterova Maria , Szarek Eva , Hussain Mehboob A. , Stratakis Constantine A. 
Published: August 2014

Abstract
Background: Carney complex (CNC) is a rare disease inherited as an autosomal dominant trait, associated with various tumors, and caused most frequently by inactivation of the PRKAR1A gene. Recently a possible association of pancreatic neoplasms with CNC was reported in 9 out of 354 patients (2.5%), suggesting the potential role of PRKAR1A as a tumor suppressor gene in the pancreas.
Methods: Prkar1afl/fl and pdx-1-CRE mice were previously reported (Kirschner et al, 2005; Lammert et al, 2001) and were kept in a mixed genetic background (C57Bl/6 x FVB). Pdx1 is a transcription factor expressed in beta-insulin producing cells and in some a-glucagon producing cells of the mouse adult pancreatic islet. Both prkar1a alleles were conditionally deleted during development by generating pdx1-Cre; prkar1af/f mice (Δ–prkar1a). Mice were phenotyped at the age of 2, 4 and 6 months and tissues were collected for histological and molecular analysis.
Results: Mice developed endocrine or mixed endocrine/acinar cell carcinomas with 100% penetration by the age of 4-5 months. Malignant behavior of the tumors was defined by stromal invasion and regional lymph node metastasis. Histologically most tumors exhibited an organoid pattern as seen in the islet-cell tumors. Some tumors exhibited in addition foci suggestive of acinar cell differentiation. The primary neuroendocrine nature of the tumor cells was confirmed by immunohistochemical (IHC) staining for chromogranin and by electron microscopy, which revealed the characteristic neuroendocrine granules. Focal acinar differentiation was further supported by the finding of scattered chymotrypsin-positive cells by immunofluorescence (IF). Although the Δ-prkar1a mice developed hypoglycemia after overnight fasting, insulin and glucagon levels in the plasma didn't differ. The negative IHC staining for the most common produced peptides (insulin, c-peptide, glucagon, gastrin, somatostatin) suggested that these tumors are non-functional. The recombination that was confirmed by the detection of the mutated allele for the prkar1a in the tumor DNA, but neither in the germline of the KO animals nor in the islets DNA of the WT mice, resulted in increased PKA activity and lack of protein expression in the tumor compared to the normal pancreatic tissue. The latter finding is suggestive of the oncogenic effect of PRKAR1A inactivation. IF staining showed that the tumor cells were composed of a pdx1+/insulin- cell-population. We hypothesized that the recently identified multipotent pdx1+/insulin- cell in the adult pancreas, gives rise to endocrine, or mixed endocrine/acinar pancreatic malignancies upon PKA manipulation.
Conclusions: Loss of prkar1a function predisposes the endocrine pancreas to invasive cancers. This supports the role of prkar1a as a tumor suppressor gene in the pancreas and provides valuable tools to evaluate novel therapeutics in endocrine pancreas malignancies.
Citation Format: Emmanouil Saloustros, Maria Tsokos, Paraskevi Salpea, Matthew Starost, Sisi Liu, Li Guang, Maria Nesterova, Eva Szarek, Mehboob A. Hussain, Constantine A. Stratakis. Genetic deletion of the prkar1a in the endocrine pancreas promotes neuroendocrine carcinogenesis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2736. doi:10.1158/1538-7445.AM2013-2736