Molecular analysis of the IL-2 receptor β chain gene expressed in human tumor cells

Abstract

Interleukin-2 (IL-2) is recognized as a T cell growth factor. We have previously reported that human carcinoma cell lines are inhibited in growth by exogenous IL-2, which binds to the IL-2 receptor β (IL-2Rβ) chain ubiquitously expressed on the surface of tumor cells. A possibility was considered that IL-2Rβ on carcinomas responsible for negative signaling was different from that expressed on hematopoietic cells. To investigate this possibility, mRNA for the IL-2Rβ chain was amplified and compared in carcinoma and lymphoid cells. Using RT–PCR with pairs of sense-antisense oligonucleotide primers specific for the various regions of extracellular, transmembrane and intracellular domains of the IL-2Rβ chain, we amplified mRNA obtained from three human carcinoma cell lines and human lymphoid cells as controls. The identity of the amplicons was confirmed by Southern analysis with the ³²P-labeled cDNA probe coding for the entire span of the IL-2Rβ chain. In addition, genomic DNA obtained from the tumor cell lines was sequenced to examine the possibility that a mutation is present in the gene coding for the intracellular IL-2Rβ chain domain. No mutations or deletions were detected. The message for all three domains of the β chain was identical in tumor cells and in normal lymphoid cells used as controls. Also, by Western blot and northern analyses no differences between IL-2Rβ chain in tumors vs that expressed in lymphoid cells were demonstrable. The IL-2Rγ chain, which participates in IL-2/IL-2R signaling pathway, was expressed in tumor cells. Expression of JAK1 transcripts in these cells was comparable to that in lymphocytes. However, RT–PCR analysis identified differences in expression of JAK3 splice variants (B and M) in tumor cells. These differences may be responsible for altered downstream signaling by IL-2. Overall, our data indicate that the same IL-2/IL-2R pathway is operative in human carcinomas and in normal epithelial or lymphoid cells.