Received for publication February 6, 2007.
Revised April 23, 2007.
Accepted for publication April 23, 2007.

Erlotinib, an Effective Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitor, Induces p27^KIP1 Upregulation and Nuclear Translocation in Association with Cell Growth Inhibition and Cell Cycle Arrest in Human Non-Small Cell Lung Cancer Cell Lines

Abstract

Erlotinib, a small molecule EGFR tyrosine kinase inhibitor, has been shown to have potent antitumor effects against human NSCLC cell growth; however, the mechanism of such effect is not elucidated. Here, we demonstrate that erlotinib-induced cell growth inhibition in EGFR high expressing human H322 NSCLC cells was accompanied by G1/S phase arrest, which was largely due to a decrease in expression of G1/S-related cyclins, suppression of activities of CDK2 and CDK4, induction of CDK inhibitor p27^KIP1, and Rb hypophosphorylation. To further understand the role of p27^KIP1 in G1/S arrest and cell growth inhibition by erlotinib, we determined its effect on the expression of p27^KIP1 at transcriptional and posttranscriptional levels. Studies using real-time RT-PCR analysis and p27 promoter-driven luciferase reporter showed that erlotinib treatment resulted in the promotion of p27 gene transcription. In addition, erlotinib treatment led to an increase in p27^KIP half-life by inhibiting p27^KIP1 phosphorylation at Thr 187 and by down-regulating Skp2 expression. Furthermore, immunofluorescence staining and cell fractionation showed that erlotinib treatment led to p27^KIP1 translocation to the nucleus. Knockdown of p27^KIP1 expression with p27^KIP1 siRNA significantly abrogated erlotinib-induced G1 phase arrest and cell growth inhibition, suggesting that induction of p27^KIP1 is required for G1 arrest and cell growth inhibition by erlotinib. Importantly, we found that G1 arrest and p27^KIP1 up-regulation by erlotinib occurred in the tested sensitive cell lines, but to lesser extent in the resistant cell lines. Taken together, these results suggest erlotinib inhibits human NSCLC cell growth predominantly by inducing p27^KIP1 expression and by suppressing cell-cycle events involved in the G1/S transition.

Key words: NGF/EGF, Mechanisms of cell killing/apoptosis

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