069 Oncogenic JAK3 mRNA isoform in cutaneous T-cell lymphoma

Mycosis fungoides (MF) and Sézary Syndrome (SS) are the most common cutaneous T-cell lymphomas (CTCLs). The exact carcinogenesis of CTCL is still unknown which limits our ability to prevent, detect, and treat CTCL. Janus kinase 3 (JAK3), a non-receptor tyrosine kinase, has been found constitutively activated and implicated in pathogenesis of CTCL. There are 3 splice isoforms or variants, JAK3S, JAK3B, and JAK3M, previously reported. The commonly described isoform or variant, JAK3S or JAK3, encodes an 1124-amino acid protein and is predominately expressed in hematopoietic cells. Recently, our transcriptome analysis by RNAseq identified a new JAK3 mRNA isoform, variant, or in-frame fusion in SS patients. This study was to validate and determine the prevalence and oncogenic role of this new JAK3 mRNA isoform in CTCL. Total RNA were extracted from sorted malignant T-cells from 33 SS patients. RT-PCR and Sanger sequencing were performed to confirm the existence of new JAK3 mRNA isoform. The expression level of new JAK3 mRNA isoform was assessed by QPCR using customized probe and primers. The Kaplan Meier survival analysis was done and correlated with the expression level of new JAK3 mRNA isoform. As a result, a new isoform JAK3 mRNA was confirmed in 13 of 33 SS patients by RT-PCR and Sanger sequencing. Its expression was detected in all 33 SS patients by QPCR, with a heterogeneous expression levels (range: 0.14 ∼ 35.43 fold-change; mean±SD: 5.25±6.85 fold-change). In contrast, only 2 out of 7 healthy donors were positive for the new JAK3 mRNA isoform, with a zero to low expression (0.08±0.06 fold-change, p<0.001). There were 19 patients with >2 fold-change gene expression while 14 patients with ≤2 fold-change. The 5-year survival of patients with higher level expression (>2 fold-change) was 42.1% in comparison with 78.6% in patients with lower expression (≤2 fold-change) (Gehan-Breslow-Wilcoxon test, p=0.0359). Our results suggest that the new JAK3 mRNA isoform may have an oncogenic role in CTCL. The study of its oncogenic function in CTCL in vitro and in vivo is ongoing.