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1: J Biol Chem. 2008 Feb 15;283(7):4189-99. Epub 2007 Nov 30.
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Intracellular interaction of interleukin-15 with its receptor alpha during production leads to mutual stabilization and increased bioactivity.

Bergamaschi C, Rosati M, Jalah R, Valentin A, Kulkarni V, Alicea C, Zhang GM, Patel V, Felber BK, Pavlakis GN.

Human Retrovirus Section, Vaccine Branch, Center for Cancer Research, NCI-Frederick, National Instsitutes of Health, MD 21702-1201, USA.

We show that co-expression of interleukin 15 (IL-15) and IL-15 receptor alpha (IL-15Ralpha) in the same cell allows for the intracellular interaction of the two proteins early after translation, resulting in increased stability and secretion of both molecules as a complex. In the absence of co-expressed IL-15Ralpha, a large portion of the produced IL-15 is rapidly degraded immediately after synthesis. Co-injection into mice of IL-15 and IL-15Ralpha expression plasmids led to significantly increased levels of the cytokine in serum as well as increased biological activity of IL-15. Examination of natural killer cells and T lymphocytes in mouse organs showed a great expansion of both cell types in the lung, liver, and spleen. The presence of IL-15Ralpha also increased the number of CD44(high) memory cells with effector phenotype (CD44(high)CD62L-). Thus, mutual stabilization of IL-15 and IL-15Ralpha leads to remarkable increases in production, stability, and tissue availability of bioactive IL-15 in vivo. The in vivo data show that the most potent form of IL-15 is as part of a complex with its receptor alpha either on the surface of the producing cells or as a soluble extracellular complex. These results explain the reason for coordinate expression of IL-15 and IL-15Ralpha in the same cell and suggest that the IL-15Ralpha is part of the active IL-15 cytokine rather than part of the receptor.

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PMID: 18055460 [PubMed - indexed for MEDLINE]