Year: 2017
Type: article
Abstract: Introduction: Somatic RHOA mutations encoding a p.Gly17Val alteration (G17 V RHOA mutation) occur in 70% of angioimmunoblastic T-cell lymphoma (AITL). RHOA, a small GTPase is converted from the GDP-bound inactive form to the active GTP-bound form by guanine nucleotide exchange factors (GEFs). The G17 V protein lacks GTP binding capacity, suggesting defects in classical RHOA signaling; however, mechanisms underlying tumorigenesis remain unknown. VAV1 serves as an important mediator of T-cell receptor (TCR) signaling pathway through its GEF-dependent and –independent function. Methods: The specific binding partner proteins of the G17 V RHOA mutant were searched by high throughput screening in Jurkat cells. Targeted deep sequencing of VAV1 was performed for 126 PTCL samples. Nuclear factor of activated T cell (NFAT) activity in response to TCR stimulation was examined in Jurkat cells transiently transfected with each G17 V RHOA and VAV1 mutant DNA. Whole transcriptome analysis was performed for Jurkat cells inducibly expressing each cDNA in response to TCR stimulation. Expression of phosphorylated VAV1 was examined by immunostaining for AITL samples. Results: High throughput screening identified VAV1 protein as a G17 V RHOA-specific binding partner. Targeted deep sequencing and RNA sequencing identified seven VAV1 alterations out of 85 RHOA mutation-negative samples (8.2%), while none of the 41 RHOA mutation-positive PTCL samples exhibited VAV1 alterations (0%). Either G17 V RHOA or VAV1-STAP2 expression enhanced phosphorylation of VAV1 at Tyr 174 in Jurkat cells. Phosphorylation was efficiently blocked by the dasatinib treatment. The G17 V RHOA and various VAV1 mutants augmented NFAT reporter activity compared to their WT or mock in Jurkat cells. Moreover, the aberrant reporter activity was also blocked by the dasatinib treatment. Gene set enrichment analysis showed that cytokine and chemokine-related pathways were enriched in Jurkat cells expressing the G17 V RHOA compared to those with WT or mock. Among 12 AITL samples, phosphorylated VAV1 was positive in all 8 AITL samples with RHOA or VAV1 mutations, whereas none of 4 samples without any mutations were stained for phosphorylated VAV1. Conclusions: The G17 V RHOA and VAV1 mutants both activate TCR pathway through hyper-phosphorylation of VAV1. Our data suggest that the RHOA-VAV1 axis in AITL may contribute to its clinical features and can be a new therapeutic target. Keywords: angioimmunoblastic T-cell lymphoma (AITL); T-cell lymphoma (TCL).
Source: Hematological Oncology
DOI: 10.1002/hon.2437_44
Institutions: University of Tsukuba, University of California, Irvine, Kyoto University, Kameda Medical Center, Tokai University, Japanese Foundation For Cancer Research, Toranomon Hospital, Hokkaido University, Kurume University, Inserm, Centre Hospitalier Universitaire Henri-Mondor, Hôpitaux Universitaires Henri-Mondor
Language: English
Subfield: Pathology and Forensic Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: bronze
OpenAlex ID: W2746643154