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Enhancement of the p27 Kip1 ‐mediated antiproliferative effect of trastuzumab (Herceptin) on HER2‐overexpressing tumor cells
Author(s) -
Marches Radu,
Uhr Jonathan W.
Publication year - 2004
Publication title -
international journal of cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.475
H-Index - 234
eISSN - 1097-0215
pISSN - 0020-7136
DOI - 10.1002/ijc.20378
Subject(s) - downregulation and upregulation , cancer research , chemistry , skbr3 , cell growth , cell cycle , cyclin dependent kinase 2 , cell , cancer cell , endocrinology , biology , medicine , cancer , biochemistry , human breast , gene
The oncogenic activity of the overexpressed HER2 tyrosine kinase receptor requires its localization in the plasma membrane. The antitumor effect of anti‐HER2 antibodies (Abs) is mainly dependent on receptor downregulation and comprises p27 Kip1 ‐mediated G 1 cell cycle arrest. However, one major limitation of anti‐HER2 therapy is the reversibility of tumor growth inhibition after discontinuation of treatment caused by the mitogenic signaling associated with cell surface receptor re‐expression. We found that the level of p27 Kip1 upregulation, inhibition of Cdk2 activity and magnitude of G 1 arrest induced by the humanized Ab trastuzumab (Herceptin, HCT) on BT474 and SKBr3 HER2‐overexpressing breast cancer cells correlates with the level of cell surface receptor. Thus, continuous exposure of cells to HCT for 72 hr results in downregulation of the cell surface receptor and a concurrent increase in the level of p27 Kip1 protein. Discontinuation of Ab exposure after the first 8 hr results in failure to upregulate p27 Kip1 and arrest of cell cycle progression. We show that the lysosomotropic amine chloroquine (CQ) augments receptor internalization in HER2‐overexpressing cells either pretreated or continuously treated with HCT and leads to an increased and sustained inhibitory effect. The enhanced CQ‐dependent loss of functional HER2 from the cell surface resulted in sustained inactivation of the serine/threonine kinase Akt, upregulation of p27 Kip1 protein and inhibition of cyclin E/Cdk2 activity. Potentiation of the inhibitory effect of HCT by CQ was directly related to loss of HER2 from the plasma membrane since prevention of Ab‐mediated receptor endocytosis by engagement of the receptor with immobilized HCT abrogated the effect of CQ. © 2004 Wiley‐Liss, Inc.