Constitutive production of IL-2 by human carcinoma cells, expression of IL-2 receptor, and tumor cell growth

Abstract

Human carcinomas spontaneously express abundant IL-2R beta but little IL-2R alpha on the cell surface, contain mRNA for IL-2R beta- and IL-2R alpha-chains, and may be inhibited in growth by exogenous IL-2. To study the relationship between IL-2R expression and growth inhibition by IL-2, carcinoma cells were transduced with IL-2R alpha and IL-2R gamma cDNAs or IL-2R beta antisense cDNA. Transfectants with the IL-2R alpha gene expressed high levels of the alpha- and beta-receptor chains and showed increased binding of [125I]IL-2. Exogenous IL-2 at the picometer concentrations inhibited their growth, and Abs to IL-2R alpha- or IL-2R beta-chains reversed the inhibition. After transduction of IL-2R beta antisense cDNA, gastric carcinoma (HR) cells no longer expressed IL-2R beta-chain, and their proliferation was depressed in the absence of exogenous IL-2. Transduction of IL-2R gamma-chain cDNA into tumor cells increased sensitivity to growth inhibition by exogenous IL-2 of a squamous cell carcinoma line, but not of HR or renal cell carcinoma lines. All of the parental and transduced tumor cell lines were found to constitutively express intracellular IL-2, detectable by immunostaining or flow cytometry of permeabilized cells. IL-2 was present on the surface of some tumor cells. Intracellular IL-2R beta and IL-2R gamma proteins were also detectable in tumor cells. Using reverse-transcription PCR combined with Southern blots or in situ hybridization, mRNA for IL-2 was found to be present in parental and transduced tumor cells. Expression on human carcinomas of IL-2R beta, inhibition of their growth by IL-2R beta antisense cDNA, and their ability to constitutively produce IL-2 and its presence on the cell surface, all suggest that endogenous IL-2 may play a role in tumor cell growth.