Altered interleukin‐2 receptor α‐chain is expressed in human T‐cell leukaemia virus type‐I‐infected T‐cell lines and human peripheral blood mononuclear cells of adult T‐cell leukaemia patients through an alternative splicing mechanism

A polymerase chain reaction (PCR) method was used to detect the interleukin‐2 receptor α ‐chain (IL‐2R α ) chain which lacks the conventional transmembrane (TM) domain in mRNA from human T‐cell leukaemia virus type‐I (HTLV‐I) ‐infected cell lines or peripheral blood mononuclear cells (PBMC) isolated from adult T‐cell leukaemia (ATL) patients. Primer pairs encompassing the TM domain were selected to generate a 357‐base pair (bp) fragment. A 146‐bp PCR product was observed consistently in addition to the target 357‐bp PCR product in mRNA from HTLV‐I‐infected cell lines, such as MT‐1, MT‐2, MT‐4 and in PBMC isolated from ATL patients. However, this 146‐bp PCR product was undetectable in HTLV‐I‐negative cell lines. The product was also detected in PBMC from normal individuals if activated in vitro with phytohaemagglutinin but not without stimulation. DNA sequence analyses revealed that exons from 5 to 7, which define a 211‐bp region containing the conventional TM domain, were deleted in the 146‐bp PCR product. The C‐terminal amino acid sequence starting from Gly 174 of the 211‐bp‐deleted molecule was distinct from that of conventional IL‐2R α as a result of an altered reading frame. We identified a 45 000 MW peptide generated from IL‐2R α mRNA through this exon skip in cell lysate of MT‐1 and MT‐2 by Western blot analyses using an antibody raised against the peptides specific to an altered IL‐2R α . Our results indicate that an altered IL‐2R α chain is expressed in HTLV‐I‐infected T lymphocytic cell lines and in ATL patients.