Activation of RHOA–VAV1 signaling in angioimmunoblastic T-cell lymphoma

Abstract

Somatic G17V RHOA mutations were found in 50–70% of angioimmunoblastic T-cell lymphoma (AITL). The mutant RHOA lacks GTP binding capacity, suggesting defects in the classical RHOA signaling. Here, we discovered the novel function of the G17V RHOA: VAV1 was identified as a G17V RHOA-specific binding partner via high-throughput screening. We found that binding of G17V RHOA to VAV1 augmented its adaptor function through phosphorylation of 174Tyr, resulting in acceleration of T-cell receptor (TCR) signaling. Enrichment of cytokine and chemokine-related pathways was also evident by the expression of G17V RHOA. We further identified VAV1 mutations and a new translocation, VAV1–STAP2, in seven of the 85 RHOA mutation-negative samples (8.2%), whereas none of the 41 RHOA mutation-positive samples exhibited VAV1 mutations. Augmentation of 174Tyr phosphorylation was also demonstrated in VAV1–STAP2. Dasatinib, a multikinase inhibitor, efficiently blocked the accelerated VAV1 phosphorylation and the associating TCR signaling by both G17V RHOA and VAV1–STAP2 expression. Phospho-VAV1 staining was demonstrated in the clinical specimens harboring G17V RHOA and VAV1 mutations at a higher frequency than those without. Our findings indicate that the G17V RHOA–VAV1 axis may provide a new therapeutic target in AITL.

Phase I/II study of dasatinib and exploratory genomic analysis in relapsed or refractory non‐Hodgkin lymphoma

“…Among the 7 patients with PTCL‐NOS histology, 2 patients achieved a durable CR, 2 patients had objective response and 1 patient had SD. Recently; it was shown that dasatinib efficiently inhibits aberrant VAV1 activation and subsequent signalling by RHOA G17V and VAV1 mutations in angioimmunoblastic T‐cell lymphoma (AITL) (Fujisawa et al , ). Consistent with this observation, 1 AITL patient in our cohort achieved a short‐lived PR.…”

Droplet digital polymerase chain reaction assay and peptide nucleic acid‐locked nucleic acid clamp method for RHOA mutation detection in angioimmunoblastic T‐cell lymphoma

“…As a result, combination of these methods increased the detection rate of RHOA mutations at the p.Gly17 position. We recently reported essential downstream signaling of G17V RHOA mutations in PTCL: the G17V mutant RHOA hyper‐activated the T‐cell receptor (TCR) signaling pathway through specific binding to VAV1 protein, an essential component in TCR signaling . The other RHOA mutants at the p.Gly17 position presumably have a similar function, although it has not been examined.…”

The new biology of PTCL‐NOS and AITL: current status and future clinical impact

“…Seven per cent of PTCL showed rearrangements of Vav guanine nucleotide exchange factor 1 (VAV1), which is normally a regulator of RHOA activity as well as other pathways. Indeed, it has been shown that RHOA (p.Gly17Val) binding to VAV1 increases TCR signalling (Fujisawa et al , ).…”

“…The understanding that activation of TCR signalling is required for lymphomagenesis may also provide new therapeutic avenues. The tyrosine kinase inhibitor dasatinib has been shown to block VAV1 phosphorylation and increased TCR signalling due to RHOA (p.Gly17Val) in a T‐cell line (Fujisawa et al , ). ITK is expressed in AITL and we have demonstrated in cell lines (Mamand et al , ) and also in a mouse model of Tfh lymphoma (Allchin et al , ) that ibrutinib, a dual ITK and Bruton's tyrosine kinase (BTK) inhibitor, can repress growth and reduce tumour size.…”