Pnck overexpression in HER-2 gene-amplified breast cancer causes Trastuzumab resistance through a paradoxical PTEN-mediated process

Abstract

The gene for Pregnancy Up-regulated Non-ubiquitous Calmodulin Kinase (Pnck), a novel calmodulin kinase, is expressed in roughly one-third of human breast tumors, but not in adjoining normal tissues. Pnck alters EGFR stability and function, prompting this study to determine if Pnck expression has implications for HER-2 function and HER-2-directed therapy. The frequency of Pnck expression in HER-2-amplified breast cancer was examined by immunohistochemistry, and the impact of Pnck expression in the presence of HER-2 amplification on cancer cell proliferation, clonogenicity, cell-cycle progression, and Trastuzumab sensitivity was examined in vitro by transfection of cells with Pnck. Cell signaling was probed by Western blot analysis and shRNA-mediated PTEN knockdown. Over 30 % of HER-2 amplified tumors were found to express Pnck. Expression of Pnck in SkBr3 cells resulted in increased proliferation, clonal growth, cell-cycle progression, and Trastuzumab resistance. Pnck expression increases Hsp27 expression, Trastuzumab partial agonist activity on HER-2 Y1248 phosphorylation, and suppressed extracellular signal-regulated kinase (ERK1/2) activity. Knockdown of endogenous PTEN upregulated ERK1/2 activity, inhibited cellular proliferation, and partially sensitized Pnck/SKBr3 cells to Trastuzumab treatment. Increased proliferation of the Pnck/SKBr3 cells was observed following expression of protein phosphatase active and lipid phosphatase dead PTEN mutant but not the total phosphatase dead PTEN mutant. Co-overexpression of HER-2 and Pnck results in enhanced tumor cell proliferation and Trastuzumab resistance that is paradoxically dependent on PTEN protein phosphatase activity. This suggests that Pnck may be a marker of Trastuzumab resistance and possibly a therapeutic target.

Metabolic history impacts mammary tumor epithelial hierarchy and early drug response in mice

“…The enhanced expression of PTEN in Dox-treated HFDO tumors appears counter-intuitive to its tumor suppressor role and the recent report that decreased PTEN function is associated with increased resistance of breast cancer cells to doxorubicin (Steelman et al , 2008). Nevertheless, our finding is consistent with PTEN-dependence of trastuzumab resistance in HER-2 gene-amplified breast cancer cells (Deb et al , 2015). The lower levels of Notch2 transcripts in HFDO vs. CDO tumors are aligned with the reported tumor-suppressive role of NOTCH 2 in human breast cancers (Parr et al , 2004).…”

Transcriptional landscape of human cancers

“…Obviously, these pathways are associated with cancer progression and metastasis characteristics such as cell interaction, cell adhesion, and cell motility. Some of the LSA genes have been shown to be overexpressed in advanced cancers and be associated with unfavorable clinical outcomes such as SOX11 [73, 74], PTPRN [75], PNCK [76] and HMGA2 [77–79]. In addition, we identified 212 genes which are upregulated in high-grade compared to low-grade cancers in more than three cancer types (Supplementary Table 13).…”

Partial agonistic effect of cetuximab on epidermal growth factor receptor and Src kinase activation in triple‑negative breast cancer cell lines

“…The ligands of RTKs possess partial agonist properties, which cause homo-or heterodimer formation and, subsequently, receptor phosphorylation and activation (23). Some antibodies directed against RTKs to block the binding of growth factors may also act as partial agonists (24)(25)(26). One study evaluating the targeting strategies of RTKs emphasised that the binding of an antibody with partial agonist properties to the receptor may cause phosphorylation, which triggers the ubiquitination and degradation of the receptor, resulting in irreversible antagonism of the RTK (26), the inhibition of the malignant response and cell proliferation, which may lead to a significant anticancer response in cancer cells.…”