SRSF2 mutations in 275 cases with chronic myelomonocytic leukemia (CMML)

Abstract

We analyzed the mutational hotspot region of SRSF2 (Pro95) in 275 cases with chronic myelomonocytic leukemia (CMML). In addition, ASXL1, CBL, EZH2, JAK2V617F, KRAS, NRAS, RUNX1, and TET2 mutations were investigated in subcohorts. Mutations in SRSF2 (SRSF2mut) were detected in 47% (129 of 275) of all cases. In detail, 120 cases had a missense mutation at Pro95, leading to a change to Pro95His, Pro95Leu, Pro95Arg, Pro95Ala, or Pro95Thr. In 9 cases, 3 new in/del mutations were observed: 7 cases with a 24-bp deletion, 1 case with a 3-bp duplication, and 1 case with a 24-bp duplication. In silico analyses predicted a damaging character for the protein structure of SRSF2 for all mutations. SRSF2mut was correlated with higher age, less pronounced anemia, and normal karyotype. SRSF2mut and EZH2mut were mutually exclusive, but SRSF2mut was associated with TET2mut. In the total cohort, no effect of SRSF2mut on survival was observed. However, in the RUNX1mut subcohort, SRSF2 Pro95His had a favorable effect on overall survival. This comprehensive mutation analysis found that 93% of all patients with CMML carried at least 1 somatic mutation in 9 recurrently mutated genes. In conclusion, these data show the importance of SRSF2mut as new diagnostic marker in CMML.

Figure 1

Schematic overview of SRSF2 protein organization, mutation type, and mutation frequency. SRSF2 consists of an RRM (AA 14-92; light gray box), a linker region (white box), and an RS-rich domain (AA 117-221; dark gray box). The 4 different mutation types and their mutation localization are indicated in red. The mutation frequency is listed and also shown as black triangles above each mutation type. Each triangle is representing 1 mutated case. From top to bottom, Pro95 missense mutations, p.Pro95_Arg102del;Pro107His, p.Arg86_Gly93dup, and p.Arg94_Pro95insArg alterations are depicted.

Figure 2

In silico analyses of the structural models of the SRSF2 in/del mutations. The structural changes of the in/del mutations were calculated with the Robetta server algorithm (http://robetta.bakerlab.org). The calculated model for the complete SRSF2wt protein (white structure) is depicted (A), the mutational hotspot Pro95 is marked in red. In addition, the enlargement shows the structure of AA 61-129 of the calculated models: p.[Pro95_Arg102del;Pro107His]; p.Arg86_Gly93dup; and p.Arg94_Pro95insArg. The Cα-Cα distance measurement of the corresponding AA of SRSF2wt to SRSF2mut is shown exemplarily for Pro95. All Å values of the Cα-Cα distance measurements for AA 88-99 are given (B).

Figure 3

Alignment of gene mutations, karyotype information, and CMML category for 275 patients. (A) Each column represents 1 of the 275 analyzed samples. Analyses of 9 investigated genes, the karyotype, and CMML category-1 or -2 are depicted by colored bars. Red bar indicates mutated gene; dark gray bar, nonmutated gene; white bar, no data available; light-gray bar, normal karyotype; black bar, aberrant karyotype; gray bar, CMML-1; and anthracite bar, CMML-2. (B) Concomitant events of SRSF2 with other mutations are also shown as a bar chart. The gray part represents SRSF2wt, the red one SRSF2mut within the analyzed subcohorts. SRSF2mut frequencies and significances (P values) are denoted; numbers of mutated/analyzed cases of the subcohorts are given in parentheses below the bars..

Figure 4

OS by Kaplan-Meier analyses of patients with CMML according to SRSF2 mutations. (A) OS of patients with SRSF2mut did not significantly differ from patients with SRSF2wt. (B) OS of patients positive for SRSF2 Pro95His compared with patients with all other SRSF2 mutations and SRSF2wt (= all other) within the RUNX1-mutated subcohort showed a favorable trend. OS is indicated in months and was compared with the 2-sided log-rank test. P values are denoted in each graph, respectively.