JAK2 gene amplification and overexpression in PMBL. (A) Southern analysis of genomic DNA extracted from 6 PMBL (a-d) and 4 DLBCL (g-j) samples, digested with EcoRI, and hybridized simultaneously with a JAK2 and a β-globin probe. The radioactivity bound to the 10-kb JAK2 genomic fragment and to the 5.5-kb β-globin genomic fragment was quantified with a phosphorimager. JAK2/β-globin ratio was 1.8 ± 0.2 in samples c to j, 8 in sample a (arrow), and 3 in sample b (arrow). (B) Quantitative RT-PCR analysis of JAK2 expression in 22 PMBL samples and 20 DLBCL samples. JAK2 mRNA levels, expressed as JAK2 mRNA copy number per 100 copies of S14 mRNA, were determined on frozen-tumor samples with no available formalin-fixed sections (), and in P-STAT6-positive (•) or P-STAT6-negative (○) tumors. Bars indicate median and interquartile values. (C) Quantitative RT-PCR analysis of JAK2 expression, performed as in panel B, in 2 PMBL-derived cell lines (MedB1 and Karpas 1106) compared with 4 DLBCL-derived cell lines (SUDHL4, SUDHL6, OCI-Ly3, and OCI-Ly10), 1 Burkitt-derived cell line (Ramos), and 1 Hodgkin-derived cell line (L428).