DDR1 is overexpressed in Hodgkin lymphoma cell lines. (A) A Q-RT-PCR assay which amplifies a sequence within the discoidin domain of DDR1 present in all known isoforms revealed that compared with GC B cells isolated from tonsils, DDR1 mRNA levels were higher in 4 of 5 Hodgkin lymphoma-derived cell lines. Normalized values were expressed relative to L540 set to a value of 1. (B) Immunoblotting for DDR1 in the same panel of cell lines showed the presence of a 126KDa protein at the expected weight of full length DDR1 and matched the levels of total DDR1 mRNA. Two representative GC B samples were DDR1 negative. DG75 cells transfected with DDR1 expression vector were used as a positive control. (C) Treatment of L591 cells with a pool of siRNAs, which recognizes all DDR1 isoforms, showed that the 126KDa band was decreased following inhibition by DDR1 RNA interference.