Abstract 51: Activating PLCG1 mutations in cutaneous T-cell lymphomas.
Authors: Vaque Jose P. , Gomez-Lopez Gonzalo , Monsalvez Veronica , Gomez de Benito Sagrario , Varela Ignacio , Martinez Nerea , Cereceda Laura , Curiel Soraya , Graña Osvaldo , Rodriguez-Pinilla Maria S. , Gonzalez-Vela Carmen M. , Rodriguez-Peralto Jose L. , Rubio-Camanillo Miriam , Martin Esperanza , Mendez Miriam , Garcia-Marco Jose A. , Provencio Mariano , Roustan Gaston , Hospital Mercedes , Suarez Dolores , Dominguez Orlando , Ortiz-Romero Pablo , Piris Miguel A. , Sanchez-Beato Margarita 
Published: August 2014

Cutaneous T-cell lymphoma (CTCL) is a heterogeneous group of diseases characterized by clonal expansion of malignant T-cells in the skin. The two predominant clinical forms of CTCL are mycosis fungoides (MF) and Sezary syndrome (SS). Tumor-stage MF has an unfavorable prognosis with a 10-year survival of approximately 40%. Despite the molecular pathogenesis of CTCL is still basically unknown, some data including Gene expression profiling (GEP) studies have shown that increased signaling from the T-cell receptor (TCR) can be considered a driving force of CTCL and that the neoplastic T-cells can acquire Treg and Th17 phenotypes. However, the molecular mechanisms responsible for this activation have not been fully clarified.

Based on the hypothesis that deregulated TCR activity may depend, at least in part, on somatic mutations, we have studied the coding exons of a selection of genes with known biological relevance in T-cells, including TCR and MAPK signaling, cytokine activity and survival/apoptosis regulators. By means of deep sequencing we analyzed paired (non tumoral vs. tumoral) genomic DNA from 11 CTCL patients. Under these premises, we first prepared enriched libraries for exons and regulatory regions for 524 genes belonging to the aforementioned pathways, and then proceeded to sequence with a Genome Analyzer GA2 (Illumina). The sequencing data was checked by FastQC and aligned to the human reference genome (GRCh37) and somatic variants were identified using GATK. Candidate variants were manually reviewed and validated by capillary sequencing.

Our results showed multiple somatic mutations in essential genes implicated in the biology of T cells. Strikingly, we found recurrent mutations in PLCG1 affecting 3/11 patients (two of them sharing the same mutation) in our cohort. This protein can be considered a mayor effector of TRC signaling as well as to play a central role in the differentiation processes of T-cells towards the acquisition of a Treg/Th17 phenotype. Using a combination of PLCG1-targeted DNA sequencing and immune-staining in FFPE patient samples, we corroborated that up to 20% of a new cohort of 60 patients harbored the recurrent PLCG1 mutation. Moreover we found a correlation between the presence of this mutation and the nuclear accumulation of activated NFAT, a well-known PLCG1downstream effector, suggesting that these mutations may confer a gain of function activity to this enzyme. We corroborated this observation by comparing the activity of exogenous expression of WT and mutant PLCG1 proteins towards the activation of NFAT using a luciferase reporter gene assay. Moreover we also found that the resultant activity from these mutants was highly sensitive to the specific inhibition of CaN and PLC in our system which may suggest that the finding of these mutations in CTCL patients might be used as an indicative for targeted therapy.

Citation Format: Jose P. Vaque, Gonzalo Gomez-Lopez, Veronica Monsalvez, Sagrario Gomez de Benito, Ignacio Varela, Nerea Martinez, Laura Cereceda, Soraya Curiel, Osvaldo Graña, Maria S. Rodriguez-Pinilla, Carmen M. Gonzalez-Vela, Jose L. Rodriguez-Peralto, Miriam Rubio-Camanillo, Esperanza Martin, Miriam Mendez, Jose A. Garcia-Marco, Mariano Provencio, Gaston Roustan, Mercedes Hospital, Dolores Suarez, Orlando Dominguez, Pablo Ortiz-Romero, Miguel A. Piris, Margarita Sanchez-Beato. Activating PLCG1 mutations in cutaneous T-cell lymphomas. [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 51. doi:10.1158/1538-7445.AM2013-51