The RHOA G17V gene mutation occurs frequently in peripheral T-cell lymphoma and is associated with a characteristic molecular signature

To the editor:

Peripheral T-cell lymphomas (PTCLs) are a group with poor outcome and nonspecific therapeutic regimens. Recently, Palomero et al¹  and Sakata-Yanagimoto et al²  identified a recurrent heterozygous mutation in the RHOA small GTPase gene encoding a p.Gly17Val alteration (G17V) that leads to inhibition of the ρ-signaling pathway. Because the RHOA/ρ-kinase pathway plays a pivotal role in many cellular functions, we wanted to establish whether the G17V mutation of the RHOA gene (RHOA-G17V) has any biological relevance in nodal PTCL (n-PTCL).

Twenty-six frozen n-PTCL-samples (13 peripheral T-cell lymphomas not specified [PTCL-NOSs], 11 angioimmunoblastic T-cell lymphomas [AITLs], and 2 anaplastic large cell lymphomas) were hybridized on a whole-human-genome oligo microarray and analyzed for the presence of the RHOA-G17V using a specific qBiomarker somatic-mutation PCR assay (SABiosciences). Expression profile data were analyzed with gene set enrichment analysis software. RHOA-G17V was found in 6 AITLs and 3 PTCL-NOSs (34.6% of cases). Thirty-two gene sets were overrepresented in the mutated subgroup of tumors. Of particular significance were the pathways related to the follicular helper CD4 T-cell and AITL signature. Moreover, other pathways of great relevance to PTCL pathogenesis, such as p38 mitogen-activated protein kinase, phosphatidylinositol 3-kinase, KRAS, the alternative nuclear factor κB (NF-κB) pathway, and the RAC1 pathway, were significantly associated with the presence of the RHOA-G17V (see supplemental Table 1 available at the Blood Web site).

The presence of RHOA-G17V was further analyzed by the previously described method in an independent consecutive series of 136 paraffin-embedded n-PTCL samples. Positive results were confirmed by Sanger sequencing of the mutated region. A total of 26.4% (32/121) of the cases carried RHOA-G17V. A total of 34.2% (25/73) of cases were AITL; 14.6% (7/48) were PTCL-NOS (P = .016), 3 of which had AITL-like features. The lower percentage of mutated cases than previously reported,^1,2  especially in AITLs, may have been due to the lower sensitivity of our assay and the paucity of tumoral cells in some AITL cases.

Immunohistochemical studies using tissue microarrays revealed a positivity for programmed cell death 1 (PD-1),³  phospho-extracellular signal-regulated kinase (p-ERK), p50, and p52 in 48.5% (66/136), 32.1% (41/136), 72.1% (98/136), and 59.6% (81/136) of patients, respectively. The presence of PD-1, nuclear p-ERK, or p52 expression was significantly positively correlated with the presence of RHOA-G17V (P = .024, 0.002, and 0.042, respectively).

There is a relationship between RHOA and Rac1 in which a high level of Rac activity leads to a reduction in that of ρ, and vice versa.⁴  Rac1 activity also activates multiple downstream effectors, including the NF-κB, p38 mitogen-activated protein kinase, and mitogen-activated protein kinase kinase/extracellular signal-regulated kinase pathways.^5,6  These findings are consistent with gene set enrichment analysis results, and some of them were validated by immunohistochemistry in an independent series of patients. However, explanations involving other biological mechanisms cannot be ruled out.⁷ 

Although standard prognostic indices for this series (International Prognostic Index and Prognostic Index for PTCL-u) identified prognostic subgroup of patients (both indices, P < .001), the mutational status of the RHOA gene did not, either in the total group of all patients or after histologic subclassification (AITL vs PTCL-NOS) (Table 1 and supplemental Tables 2-3 available on the Blood Web site.).

We and other researchers have previously reported the usefulness of NF-κB, phosphatidylinositol 3-kinase/AKT, and extracellular signal-regulated kinase pathway inhibitors for treating PTCL patients.^8,9  The findings presented here suggest that RHOA-G17V could identify patients who are sensitive to some of these inhibitors. Further clinical and biological studies are needed to validate these results.