Extensive alternative splicing of interleukin-7 in malignant hematopoieticcells: Implication of distinct isoforms in modulating IL-7 activity

Interleukin-7 (IL-7) plays a pivotal role in early stages of normal B and T cell development. In addition, IL-7 stimulates the proliferation of both a ntitumor reactive cells and a number of T and B cell malignancies, underlin ing its significance for leukemogenesis, However, its exact role in the pro cess of pathologic maturation of lymphocytes and regulation of the immune r esponse is not completely understood. As alternative splicing of pre-mRNA h as been shown to be involved in the control of gene expression, and splicin g-derived protein isoforms with antagonistic activity have been found, we a ssessed the mRNA-expression of IL-7 and its previously described alternativ e splice variant lacking exon 4, IL-7 delta 4, in leukemic cells from child ren with acute lymphoblastic leukemia (ALL). PCR of full-length IL-7 cDNA e nabling the competitive amplification of both variants led to the amplifica tion of diverse unexpected PCR products. The sequence data demonstrated the existence of three additional in-frame splice variants resulting from exon skipping of exon 3 or exon 5 or both in combination with exon 4, We named these IL-7 delta 3/4, IL-7 delta 4/5, and IL-7 delta 3/4/5. Furthermore, th ree out-of-frame splice variants were identified, IL-7(-56bp(Exon2)), IL-7 delta 4(-56bP(Exon2)), and IL-7 delta 3/4/5(-56bp(Exon2)), in which, in add ition to the aforementioned exon skipping, 56 bp of the 3' end of exon 2 ar e omitted, Our results led us to assume that splicing-derived IL-7 isoforms play a potential role in modulating IL-7-mediated biologic effects. Furthe r studies are required to clarify the significance of the diverse IL-7 prot ein isoforms for the regulation of IL-7 function and the pathogenesis of le ukemia.