Direct inhibition of interleukin‐2 receptor α‐mediated signaling pathway induces G₁ arrest and apoptosis in human head‐and‐neck cancer cells

Abstract

Overexpression of the interleukin-2 receptor (IL-2R) alpha chain in tumor cells is associated with tumor progression and a poor patient prognosis. IL-2Ralpha is responsible for the high affinity binding of the receptor to IL-2, leading to activation of several proliferative and anti-apoptotic intracellular signaling pathways. We have previously shown that human squamous cell carcinoma of a head-and-neck line (PCI-13) genetically engineered to overexpress IL-2Ralpha exhibit increased transforming activity, proliferation, and drug resistance, compared to the vector control cells (J Cell Biochem 2003;89:824-836). In this study, we report that IL-2Ralpha(+) cells express high levels of total and phosphorylated Jak3 protein and are more resistant to apoptosis induced by a Jak3 inhibitor than the control LacZ cells. Furthermore, we used daclizumab, a monoclonal antibody specific to IL-2Ralpha, and determined the effects of IL-2Ralpha inhibition on cell cycle and apoptosis as well as the involvement of potential cell cycle and apoptosis regulatory proteins. We found that daclizumab induces G(1) arrest, associated with down-regulation of cyclin A protein, preferentially in IL-2Ralpha(+) cells, but not in LacZ cells. In addition, daclizumab activates apoptotic death program via Bcl-2 down-regulation preferentially in IL-2Ralpha(+) cells. Finally, daclizumab also sensitizes IL-2Ralpha(+) cells to other apoptotic stimuli, although the effect is moderate. These results indicate that daclizumab inhibits the proliferative potential of IL-2Ralpha(+) cells via inhibition of cell cycle progression and induction of apoptosis.

The role of interleukin-2 receptor alpha in cancer

“…We found that daclizumab effectively inhibited the proliferation of IL-2Ralpha+ cells, but not the vector control cells (112). The cell cycle distribution pattern differs dramatically between the untreated IL-2Ralpha+ and LacZ cells: while 59% of the IL-2Ralpha+ cells are in G 2 -M phase, 50% of the LacZ cells reside in G 0 -G 1 phase (67,112).…”

“…We found that IL-2Ralpha+ cells were sensitized by the mAb, but the effect was moderate (112). A possible explanation for the modest effect of daclizumab on the sensitization to the apoptosis-inducing drugs may be linked to the arrest of the cells in G 0 /G 1 after daclizumab treatment (112). Previous reports have shown that arresting cells in G 0 /G 1 confers resistance to multiple apoptotic stimuli (113)(114)(115).…”

“…To test this hypothesis, we pretreated cells with daclizumab, followed by introduction of LLnL, VP-16, and Taxol. We found that IL-2Ralpha+ cells were sensitized by the mAb, but the effect was moderate (112). A possible explanation for the modest effect of daclizumab on the sensitization to the apoptosis-inducing drugs may be linked to the arrest of the cells in G 0 /G 1 after daclizumab treatment (112).…”

“…Treatment with daclizumab for 72 h effectively inhibited cell cycle progression in the IL-2Ralpha+ cells with a 57% increase of the cells in G 0 -G 1 , compared to LacZ, which only increased ~20%. A decrease in cyclin A protein expression (dose-and time-dependent) was observed only in IL-2Ralpha+ cells (112). Therefore, daclizumab selectively and effectively inhibits cell cycle progression in IL-2Ralpha+ cells.…”

“…Daclizumab did not induce caspase-3 activation in LacZ cells. Conversely, IL-2Ralpha+ cells treated with daclizumab induced caspase-3 activity (3.5fold) and increased the overall caspase activity by ~50% (112).…”