Prognostic Significance of Reduced BCAS4 expression in Bone Marrow Cells of Patients with Myelodysplastic Syndromes

Deletion of long arm of chromosome 20 (del(20q)) is commonly observed in myelodysplastic syndromes (MDS). Reduced expression of genes located within the common deleted region (CDR) of del(20q) due to haploinsufficiency may play a role in molecular pathogenesis of MDS. In the previous study, we examined expression of genes located within the CDR which we determined using array-CGH, in bone marrow mononuclear cells in MDS patients with or without del(20q), indicating that BCAS4 expression was significantly reduced in bone marrow cells in MDS patients with or without del(20q). The BCAS4 gene, which was identified as a fusion transcript expressed in MCF7 cells, encodes 23kD protein. Although function of BCAS4 protein remains unclear, it could be a member of "cappuccino" family, which belong to lysosome-related organelles. Abnormality of genes encoding lysosome-related organelles cause variety of congenital disorders, including the Hermansky-Pudlak syndromes, which is characterized by oculocutaneous albinism and bleeding tendency due to platelet dysfunction as a result of lysosome abnormalities. In the present study we investigated clinical implication of BCAS4 expression level in MDS patients.

Mononuclear cells separated from bone marrow samples taken at the time of MDS diagnosis were used for analysis. Written informed consent was obtained from patients before study. To analyze BCAS4 expression, quantitative RT-PCR was performed using cDNA from mononuclear cells as template by the TaqMan probe method (Applied Biosystems) with co-amplification of the endogenous control gene, human GAPDH (Applied Biosystems). Samples from 103 MDS patients, 64 males and 39 females with median age of 67 years (range: 20-91 years), with (n=14) or without (n=89) del(20q), were examined in the present study. Patients were classified as RCUD (n=12), RCMD (n=55), RARS (n=9), RAEB-1 (n=10), and RAEB-2 (n=13), according to WHO 2008 classification, and in RAEB-T (n=4) according to FAB classification. They also were categorized in four IPSS risk groups, low risk (n=30), intermediate-1 risk (n=46), intermediate-2 risk (n=18), and high risk (n=9).

There was no significant difference in relative BCAS4 expression level between patients with del(20q) and those without del(20q), and among WHO subtypes. Higher IPSS risk groups (INT-2 and High) showed trend in association with reduced BCAS4 expression compared with lower IPSS risk groups (Low and INT-1) (P=0.104). We analyzed impact of BCAS4 expression on overall survival (OS). Based on BCAS4 expression level, 103 patients were divided into four groups, highest (Q1), intermediate (Q2, Q3), and lowest (Q4) quartiles. The Kaplan-Meier analysis demonstrated that Q4 showed significantly worse OS compared with remaining quartiles (Q1-Q3) (log-rank test, P=0.0031). The estimated 2-year OS rates in Q1-3 group and Q4 group were 75.1% and 48.9%, respectively. According to the COX proportional hazards model, univariate analysis showed lower BCAS4 expression (Q4 vs Q1-Q3) was associated with worse OS (hazard ratio 3.43, 95%CI 1.89-6.11, P=0.0001) as well as older age (65 years or older vs less than 65 years), and higher IPSS risk groups (INT-2 and High vs Low and INT-1). Multivariate analysis indicated that lower BCAS4 expression showed trend for association with worse OS (hazard ratio 1.90, 95%CI 0.96-3.64, P=0.0651) by analyzing with two variables (older age and higher IPSS groups). Next, we investigated whether OS is predicted by combination of three variables, BCAS4 expression level, IPSS risk groups, and age at diagnosis. We defined lower BCAS4 expression (Q4), higher IPSS (INT-2 and High), and older age (65 years or older), as risk factors. The Kaplan-Meier analysis showed that survival curves were well separated according to number of risk factors (0, 1, and 2 or more) (P<0.0001). The estimated 1-year, 2-year, and 5-year survival rates were 100%, 100%, and 86.5% in patients without risk factor, 75%, 70.2%, and 51.7% in patients with one risk factor, and 54%, 34.3%, and 11.4% in patients with two or more risk factors.

The present study demonstrated that reduced BCAS4 expression is associated with inferior clinical outcome, indicating that BCAS4 expression level could be a useful prognostic marker in MDS, especially by combination with IPSS risk and patients age at diagnosis.