5q+ MDS Patients with Low RPS14 Expression Are Candidates to Immune-Modulating Drugs

Introduction

Heterozygous deletion of RPS14 occurs in isolated interstitial deletion of chromosome 5q in patients with myelodysplastic syndrome (MDS). 5q- MDS has been linked to impaired erythropoiesis and it is characterized by a constant macrocytic anemia and normal or high platelet counts associated with hypolobulated megakaryocytes. Previous studies have detected reduced RPS14 expression in more than 50% of non-5q-patients, which has been associated with increased apoptosis of nucleated erythrocytes. Although the role of RPS14 in 5q+ patients remains unknown, recently, it has been demonstrated its implication in human erythropoiesis during 5q- MDS pathology and during lenalidomide response: RPS14 haploinsufficiency produces the activation of p53 and its target p21 in erythroid cells, resulting in cell cycle arrest and apoptosis. Moreover, SPARC and CSNK1A1 haploinsufficiencies promote lenalidomide action. As non-5q- patients expressing low levels of RPS14 will also be potentially beneficed by lenalidomide therapy, we explored this scenario. In addition, we explore the possible origin of the altered RPS14 expression in this group of patients and its potential link with 5q- pathology.

Methods

DNA and RNA were extracted from the bone marrow of 93 MDS patients and ten controls. In order to explore the origin of RPS14 low expression in non-5q- MDS patients, we analysed potential mutations in RPS14 gene and 32 genes related with MDS using Ion Proton sequencing, using a coverage of 2000x.

We also studied expression changes in other key genes involved in the development of the 5q- disease, including the tumour suppressor gene SPARC and the putative tumour suppressor gene CSNK1A1, contained in the commonly deleted region. For this, RPS14, SPARC, CSNK1A1 and p21 mRNA levels were analysed by real time PCR using Taqman probes in a 7500 RT PCR System. β-glucuronidase gene was used as endogenous reference to normalize data. Samples were classified by RPS14 expression levels and differences in SPARC, CSNK1A1 and p21 expression mean values between the two groups were analyzed using the Mann-Whitney U test.

Results

All the patients analysed except one did not present any mutation in RPS14 gene. This patient was a 5q+ MDS patient showing two mutations: downstream and within an intronic region of the gene. Nevertheless, this 5q+ patient did not present low RPS14 levels. Thus, the origin of RPS14 decreased expression seems not to be related with genomic alterations in the RPS14 coding region. On the other hand, mutational analysis of 32 MDS-related genes revealed a higher frequency of mutations in CBL, U2AF1 and SF3B1 in the group of patients with low RPS14 levels (figure 1a).

As it has been previously reported, non-5q- patients expressing low levels of RPS14 presented higher survival probability in the IPSS lower risk group. This data, in addition with a tendency for increased p21 expression (figure 1b), suggest that this group could be beneficed by lenalidomide therapy. Moreover, we also observed a significant decrease CSNK1A1 expression (figure 1d), as well as a significant increase of SPARC levels (figure 1c) in patients with low levels of RPS14.

Conclusion

Although the important role of RPS14 in MDS pathology has been recently demonstrated, the origin of RPS14 downregulation in about 50% non-5q- patients remains unknown. Our results suggest that the origin of RPS14 decreased expression is not related with a RPS14 genomic alteration. Nevertheless, mutations found in U2AF1, SF3B1 and CBL could play a role in RPS14 downregulation. On the other hand, the alterations observed in p21, CSNK1A1 and SPARC expression suggest the potential use of lenalidomide in this group of patients.

M.L. hold a postdoctoral Fellowship of the Spanish Ministry of Economy and Competitiveness (FPDI-2013-16409)

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