Trastuzumab-induced HER2 phosphorylation: exploring the mechanisms and implications

Targeting of ErbB family of receptor tyrosine kinases (RTKs) is frequently used to inhibit the oncogenic signaling in different malignancies. Lapatinib, a dual selective tyrosine kinase inhibitor (TKI) of EGFR and HER2, inhibits their tyrosine kinase activities and receptor tyrosine phosphorylation. Cetuximab, a chimeric monoclonal antibody (mAb) directed against the extracellular domain of EGFR, prevents EGF-mediated receptor kinase activation and tyrosine phosphorylation. However, trastuzumab, a humanized mAb directed against HER2, induces EGFR and HER2 receptor tyrosine phosphorylation and this agonistic effect is correlated with its inhibition of cancer cell proliferation. This review will focus on the current understanding of molecular mechanisms and implications of trastuzumab-induced tyrosine phosphorylation of HER2

Growth inhibitory targets of retinoids.

Growth inhibitory targets of retinoids

Histone sumoylation is a negative regulator in Saccharomyces cerevisiae and shows dynamic interplay with positive-acting histone modifications

Covalent histone post-translational modifications such as acetylation, methylation, phosphorylation, and ubiquitylation play pivotal roles in regulating many cellular processes, including transcription, response to DNA damage, and epigenetic control. Although positive-acting post-translational modifications have been studied in Saccharomyces cerevisiae, histone modifications that are associated with transcriptional repression have not been shown to occur in this yeast. Here, we provide evidence that histone sumoylation negatively regulates transcription in S. cerevisiae. We show that all four core histones are sumoylated and identify specific sites of sumoylation in histones H2A, H2B, and H4. We demonstrate that histone sumoylation sites are involved directly in transcriptional repression. Further, while histone sumoylation occurs at all loci tested throughout the genome, slightly higher levels occur proximal to telomeres. We observe a dynamic interplay between histone sumoylation and either acetylation or ubiquitylation, where sumoylation serves as a potential block to these activating modifications. These results indicate that sumoylation is the first negative histone modification to be identified in S. cerevisiae and further suggest that sumoylation may serve as a general dynamic mark to oppose transcription

Electron microscopy imaging of cardiomyocyte ultrastuctures.

<p>Two mice from trastuzumab-treated and two mice from vehicle-treated groups were evaluated by EM. Animals were either treated daily with trastuzumab (10 mg/kg) or with vehicle control. On day 7, mice were euthanized and the hearts were harvested. See materials and methods for details of the fixation, embedding, and staining procedures. (<b>a</b>) A representative section of the left ventricle from a control mouse (<b>a1</b>) showing the typical mitochondrial density and intimate contacts (green arrows), connected myofibers (red arrows) and normal thickness of myofibers (pairs of blue arrows), compared to a section from trastuzumab-treated mice (<b>a2</b>) showing sporadic mitochondrial (green arrows), damaged disconnected myofibers (red arrows) and thinner myofibers (pairs of blue arrows). (<b>b</b>) Bar graph, quantification of damaged myofibers in trastuzumab-treated animals compared to control mice. Data are presented as a percentage of damaged and discontinued myofibers out of the total numbers of myofibers in the segment. (<b>c</b>) Bar graph showing a quantification of the distance between mitochondrial in trastuzumab-treated animals compared to control animals. Data presented in µm representing an average distance between mitochondria in the image. Magnification, 1000X (<b>d</b>) Bar graph showing a measurement of myofibers thickness in trastuzumab-treated animals compared to control mice. Data presented in µm representing the average thickness of myofibers. Magnification, 1000X. (<b>e</b>) Bar graph showing quantification of the number of mitochondria in sections from trastuzumab-treated animals compared to control mice. Data presented as average number of mitochondrial per segment. (f) Bar graph showing the percentage of damaged mitochondria (membrane disintegration, thinning of cristae and significant cavelae formation). In this figure, similar segments from the two animals in each group were used for this quantification. Student’s t-test was used to compare the two groups and significance is determined as *P < 0.05 or ** P < 0.01 vs. the vehicle treated animals.</p

Trastuzumab altered the expression of genes that are essential for cardiac functions.

<p>(a) Heatmap representation of differentially expressed genes in the trastuzumab-treated animals compared to the control vehicle injected animals (blue = downregulation and red = upregulation); n=4 for each group. (b) Bar graph showing microarray results as Log₂ of fold change. (c) Bar graph showing the qPCR validation of randomly selected genes from the microarray data. Results are shown as log₂ of fold change. Analysis of variance was used to determine those probe sets significantly different between the two groups. The gene list was filtered with a fold-change cutoff of 2.</p

Trastuzumab induces oxidative stress and increases Caspase 3/7 activity in cardiomyocytes.

<p>(<b>a</b>) Quantification of ELISA measurement of NT in the hearts of animals treated with trastuzumab compared to the control vehicle injected animals. (<b>b</b>) Quantification of ELISA measurement of 4-HNE adducts in the hearts of animals treated with trastuzumab compared to the control vehicle injected animals. (<b>c</b>) Quantification of ELISA measurement of caspase 3 and 7 in the trastuzumab-treated animals compared to the control vehicle injected animals. For all the graphs in Figure 4, the results are expressed as fold changes relative to that of control vehicle-treated animals. Student’s t-test was used to compare the two groups and significance is determined as *P < 0.05 or **P< 0.01 vs. the vehicle treated animals. At least six animal were used for each group (n=6). </p

Trastuzumab impairs systolic function in mice.

<p>Mice received either trastuzumab (10mg/kg/day) (N = 10) or vehicle injections (N = 6). VEF (a),FS (b), heart rate (d), LVPW thickness (c), left ventricular systolic (f) and diastolic (e) diameter were evaluated at base line (day 0), and days 3 and 7 post injection. Data are presented as percentage of control animals (mean ± SEM). *P < 0.05 vs. the vehicle treated animals.</p