Calpain regulates sensitivity to trastuzumab and survival in HER2-positive breast cancer

Abstract

Resistance to anti-HER2 (human epithelial growth factor receptor 2) trastuzumab therapy occurs commonly in HER2-positive breast cancer and involves overactivation of HER2 and/or AKT1. Using the model of trastuzumabsensitive or trastuzumab-resistant HER2-positive cells with wild-type PTEN, negative regulator of AKT1, we explore the involvement of cysteine protease calpain in mechanisms of trastuzumab resistance. Overexpression of calpain1 or activation of endogenous calpain during adhesion or trastuzumab treatment of trastuzumabsensitive cells induces cleavage of cytoplasmic domains of HER2/phospho-HER2; cleavage occurs in HER2-positive tumors. Expression of the catalytically inactive mutant of calpain1 reduces the cleavage to enhance the activity of HER2, inactivates PTEN to enhance the activation of AKT1, induces desensitization to trastuzumab and promotes survival of trastuzumab-sensitive cells. In the model of trastuzumab resistance, constitutive overactivation of HER2 and AKT1 correlates with reduced activation of calpain. Moreover, inhibitors of the catalytic site of calpain reduce the increase in constitutive activity of AKT1 and survival of trastuzumab-resistant cells selectively. Together, by regulating the activation of HER2 and PTEN/AKT1, calpain regulates trastuzumab sensitivity and survival, and the deregulation of the activation of calpain promotes trastuzumab resistance. Trastuzumab-resistant cells activate AKT1 in a mechanism dependent on the residual calpain activity, inhibition of which restores trastuzumab sensitivity and rescues resistance. These data identify calpain as a new therapeutic target in HER2-positive breast cancer.

A Major Role of p95/611-CTF, a Carboxy-Terminal Fragment of HER2, in the Down-modulation of the Estrogen Receptor in HER2-Positive Breast Cancers

“…Following this assumption and because the molecular weight of proteins varies with cell-specific posttranslational modifications, samples from breast tumors analyzed by Western blot were classified as p95HER2-positive if immunoreactivity was detected in the 90 to 115 kDa region. Additional fragments arise through proteolytic cleavage of the intracellular domain of HER2 by caspases (33) and calpains (34). However, the molecular size of these fragments is <50 kDa (33,34), and therefore, they have not been considered within the p95HER2 group of fragments.…”

“…Additional fragments arise through proteolytic cleavage of the intracellular domain of HER2 by caspases (33) and calpains (34). However, the molecular size of these fragments is <50 kDa (33,34), and therefore, they have not been considered within the p95HER2 group of fragments. In contrast to the original hypothesis, we have shown recently that, in addition to proteolytic processing, alternative initiation of translation from different methionine codons can generate HER2 CTFs (21).…”

Calpain 2 Regulates Akt-FoxO-p27Kip1 Protein Signaling Pathway in Mammary Carcinoma

“…Interestingly, a recent report showed that calpain inhibition could resensitize herceptin-resistant variants of these HER2 ϩ cells (36). Calpain knock-out in the chondrocyte lineage in mice has also been associated with decreased proliferation correlating with increased p27…”

Calpain in Breast Cancer: Role in Disease Progression and Treatment Response

“…data]. In vitro studies have shown that calpain-4 enhances survival following trastuzumab treatment; however, suppression of calpain-1 activity has also been linked with trastuzumab response in HER2-positive breast cancer cell lines [103,104]. How the calpain system may regulate the response to trastuzumab is unclear, but evidence indicates that calpain- mediated cleavage of IκBα is involved in HER2-induced NF-κB activation and, inversely, that HER2 overexpression blocks calpain activity by up-regulating calpastatin [48,105].…”