Cloning and expression of an alternatively spliced mRNA encoding a soluble form of the human interleukin-6 signal transducer gp130.

The membrane-bound gp130 glycoprotein acts as an affinity converting and signal transducing receptor (R) for interleukin-6 and several other cytokines. In this work, we RT-PCR amplified gp130 cDNA using primers flanking the sequence encoding the transmembrane domain of gp130. We observed in blood mononuclear cells, in addition to the expected 333-bp length fragment, a second major band of 418 bp. Sequencing of the 418-bp fragment and its genomic counterpart showed a new 85-bp exon located in the sequence encoding the extracellular region of the gp130 protein. This exon is most likely due to alternative splicing and leads to a frame-shift resulting in a stop-codon 1 bp before the transmembrane coding region. Correspondingly, supernatants from chinese hamster ovary cells transfected with this cDNA contained 4-5 times more soluble (s) gp130 than supernatants from cells transfected with a cDNA encoding the membrane-bound gp130 protein. Both gp130 and alternatively spliced sgp130 were also transcribed by the myeloma cell lines XG-1, XG-2, XG-4, XG-4CNTF XG-6, XG-7, XG-9, XG-10, U266 and RPMI 8226. However, XG-4A cells derived from XG-4 cells, but growing independently of exogenous IL-6, did not transcribe sgp130 mRNA. A possible interference with intracrine stimulatory factors by alternatively spliced sgp130 needs to be further investigated.