MicroRNAs miR-7 and miR-340 predict response to neoadjuvant chemotherapy in breast cancer.

PURPOSE: miRNAs have been linked to chemosensitivity of breast cancer cells in vitro. In patients, however, there is no clinically validated method for predicting chemotherapy response. The aim of this study was to assess whether (I) a specific pattern of miRNA expression in pretherapeutic biopsies can predict response to neoadjuvant chemotherapy, and (II) differential miRNA expression in residual tumor after completion of chemotherapy allows further prognostic stratification of non-responding patients. METHODS: Sixty-four patients with newly diagnosed large (≥3 cm) or locally advanced primary breast cancers who underwent neoadjuvant anthracycline/taxane-based chemotherapy were included. Relative expression of 10 miRNAs likely to be associated with chemotherapy response (miR-7,-21,-29a,-29b,-34a,-125b,-155,-200c,-340,-451) was determined by quantitative RT-PCR from pretherapeutic biopsies (n = 64) and residual invasive tumor after chemotherapy (n = 42). Pathologic complete response (pCR) defined by absence of invasive tumor served as reference standard. In addition, miRNA expression was compared with disease-free and overall survival. RESULTS: Nine (14%) of 64 patients achieved pCR. High expression of miR-7 and low expression of miR-340 in pretherapeutic biopsies predicted pCR with a negative predictive value of 96 and 97%, respectively (specificity 54 and 57%). The combined profile of miR-7high/miR-340low demonstrated improved specificity of 86% while maintaining a high negative predictive value (96%) to identify non-responders. Pretherapeutic expression of miR-200c and miR-155 showed prognostic information, and low expression was associated with increased overall survival (115 vs. 90 months, p ≤ 0.03). After chemotherapy, the overall survival of patients with residual invasive tumor was better for those demonstrating low miR-7 or high miR-125b (p = 0.01). CONCLUSIONS: Intratumoral expression of miR-7 and miR-340 prior to neoadjuvant chemotherapy could be used to predict pCR and a profile of miR-7low or miR-340high identified patients unlikely to achieve pCR who might benefit from alternative treatment options including earlier surgery. Our study identifies miRNAs as promising predictive biomarkers, which could aid in optimization of breast cancer management and treatment stratification.

Growth factor receptor-bound protein 2 promotes autophagic removal of amyloid-ß protein precursor intracellular domain overload in neuronal cells.

The ascertainment of elevated levels of amyloid-ß protein precursor intracellular domain (AICD) in Alzheimer's disease (AD) brains and the fact that it contributes to AD-like pathology has geared the search toward a new paradigm. While studying endogenous as well as overexpressed Grb2-AICD interaction in AD cell models, it was found that Grb2 co-localized to compartments along with AICD. We report now that these vesicles form in a clathrin and dynamin independent manner. Both types of vesicles mature into autophagosomes, merge with lysosomes, and relieve the cells of AICD overload. Inhibiting autophagosome formation results in vesicle accumulation. AICD-level is reduced in Grb2 excess condition in Cycloheximide Chase setup. Reduced caspase activity and apoptosis point toward the fact that the cytotoxic effect of AICD is alleviated by its sequestration in autolysosomes. Hence we state that the entrapping of AICD in Grb2 vesicles and its clearance via autophagosomes is a survival contrivance on the part of the cell. This study unravels, for the first time, the roles of Grb2 in autophagy and in handling toxic protein overload in an AD-like scenario.

The N-terminal SH3 domain of Grb2 is required for endosomal localization of AßPP.

Based on the observations that Grb2 overexpression altered the trafficking route of amyloid-ß protein precursor (AßPP) by inhibiting its release via exosomal vesicles, and subsequently increased its endogenous level, in the present study we aimed to elucidate the mechanism of traffic impairment and the role of different Grb2 domains in this process. We found that the N-SH3 domain of Grb2 was involved in the protein vesicular localization. The C-SH3 domain could also form very small puncta, but were not characteristic Grb2 containing vesicles. Vesicles containing the N-SH3-SH2 domain had a mixed population of early and late endosomes but C-SH3-SH2 domain containing vesicles were of early endosomal type. The N-SH3 domain therefore seems to be involved in the maturation of early endosomes to late endosomes. Almost all the features shown by overexpression of full-length type Grb2, for example, entrapment of endogenous AßPP in vesicles, affecting the turnover of AßPP in terms of decrease in exosomal release and increase in endogenous concentration of the protein, could be reproduced by the N-SH3-SH2 domain and, to a very limited extent, by the C-SH3-SH2 domain. The middle SH2 domain alone did not show any involvement in AßPP trafficking. By mutational analysis of both N and C terminal SH3 domains, attempts were made to elucidate the molecular basis of this functional anomaly.

Common protein biomarkers assessed by reverse phase protein arrays show considerable intratumoral heterogeneity in breast cancer tissues.

Proteins are used as prognostic and predictive biomarkers in breast cancer. However, the variability of protein expression within the same tumor is not well studied. The aim of this study was to assess intratumoral heterogeneity in protein expression levels by reverse-phase-protein-arrays (RPPA) (i) within primary breast cancers and (ii) between axillary lymph node metastases from the same patient. Protein was extracted from 106 paraffin-embedded samples from 15 large (≥3 cm) primary invasive breast cancers, including different zones within the primary tumor (peripheral, intermediate, central) as well as 2-5 axillary lymph node metastases in 8 cases. Expression of 35 proteins including 15 phosphorylated proteins representing the HER2, EGFR, and uPA/PAI-1 signaling pathways was assessed using reverse-phase-protein-arrays. All 35 proteins showed considerable intratumoral heterogeneity within primary breast cancers with a mean coefficient of variation (CV) of 31% (range 22-43%). There were no significant differences between phosphorylated (CV 32%) and non-phosphorylated proteins (CV 31%) and in the extent of intratumoral heterogeneity within a defined tumor zone (CV 28%, range 18-38%) or between different tumor zones (CV 24%, range 17-38%). Lymph node metastases from the same patient showed a similar heterogeneity in protein expression (CV 27%, range 18-34%). In comparison, the variation amongst different patients was higher in primary tumors (CV 51%, range 29-98%) and lymph node metastases (CV 65%, range 40-146%). Several proteins showed significant differential expression between different tumor stages, grades, histological subtypes and hormone receptor status. Commonly used protein biomarkers of breast cancer, including proteins from HER2, uPA/PAI-1 and EGFR signaling pathways showed higher than previously reported intratumoral heterogeneity of expression levels both within primary breast cancers and between lymph node metastases from the same patient. Assessment of proteins as diagnostic or prognostic markers may require tumor sampling in several distinct locations to avoid sampling bias.

Intratumoral heterogeneity of microRNA expression in breast cancer.

Profiling studies have identified specific microRNA (miRNA) signatures in malignant tumors including breast cancer. Our aim was to assess intratumoral heterogeneity in miRNA expression levels within primary breast cancers and between axillary lymph node metastases from the same patient. Specimens of 16 primary breast cancers were sampled in 8-10 distinct locations including the peripheral, intermediate, and central tumor zones, as well as two to five axillary lymph node metastases (n = 9). Total RNA was extracted from 132 paraffin-embedded samples, and the expression of miR-10b, miR-210, miR-31, and miR-335 was assessed as well as the reproducibility of RNA extraction and miRNA analysis by quantitative RT-PCR. Considerable intratumoral heterogeneity existed for all four miRNAs within primary breast cancers (CV 40%). No significant differences within (CV 34%) or between different tumor zones (CV 33%) were found. A similar variation in miRNA expression was observed between corresponding lymph node metastases (mean CV 40%). In comparison, the variation among different patients showed a CV of 80% for primary tumors and 103% for lymph node metastases. Both miRNA extraction procedures and quantitative RT-PCR showed high reproducibility (CV ≤ 2%). Thus, the intratumoral heterogeneity of miRNA expression in breast cancers can lead to significant sampling bias. Assessment of breast cancer miRNA profiles may require sampling at several different tumor locations and of several tumor-involved lymph nodes when deriving miRNA expression profiles of metastases.

Functional implications of the conformational switch in AICD peptide upon binding to Grb2-SH2 domain.

It has been hypothesized previously that synergistic effect of both amyloid precursor protein intracellular C-terminal domain (AICD) and Aß aggregation could contribute to Alzheimer's disease pathogenesis. Structural studies of AICD have found no stable globular fold over a broad range of pH. Present work is based on the premises that a conformational switch involving the flipping of C-terminal helix of AICD would be essential for effective binding with the Src homology 2 (SH2) domain of growth factor receptor binding protein-2 (Grb2) and subsequent initiation of Grb2-mediated endo-lysosomal pathway. High-resolution crystal structures of Grb2-SH2 domain bound to AICD peptides reveal a unique mode of binding where the peptides assume a noncanonical conformation that is unlike other structures of AICD peptides bound to protein-tyrosine-binding domains or that of its free state; rather, a flipping of the C-terminal helix of AICD is evident. The involvement of different AICD residues in Grb2-SH2 interaction is further elucidated through fluorescence-based assays. Our results reveal the significance of a specific interaction of the two molecules to optimize the rapid transport of AICD inside endosomal vesicles presumably to reduce the cytotoxic load.

AICD Overexpression in Neuro 2A Cells Regulates Expression of PTCH1 and TRPC5.

Amyloid precursor protein (APP), implicated in Alzheimer's disease, is a transmembrane protein of undetermined function. APP is cleaved by gamma-secretase that releases the APP intracellular domain (AICD) in the cytoplasm. In vitro and in vivo studies have implicated the role of AICD in cell signaling and transcriptional regulation of Gsk3ß, KAI1, BACE1, EGFR, and other proteins. In this study, by overexpressing AICD in mouse neuroblastoma cell lines, we have demonstrated the alteration in the expressions of two proteins, patched homolog 1 (PTCH1), a receptor for sonic hedgehog signaling, and transient receptor potential cation channel subfamily C member 5 (TRPC5), a component of receptor-activated nonselective calcium permeant cation channel. Our results indicate the possibility of regulation by AICD in developmental processes as well as in the maintenance of calcium homeostasis at the transcription level.

Grb2-mediated alteration in the trafficking of AbetaPP: insights from Grb2-AICD interaction.

The amyloid-beta protein precursor (AbetaPP) is processed by various proteases located along the endosomal lysosomal pathway and any alteration in its trafficking would be important in the pathogenesis of Alzheimer's disease (AD). Our current study is based on the clinical evidence that an AbetaPP intracellular domain (AICD) "adaptor" protein, growth factor receptor protein binding protein 2 (Grb2), gets concentrated in neuronal cell bodies in AD patients. Here we show that both endogenous and exogenously transfected Grb2 interact with AbetaPP in Neuro 2A cells. Endogenous Grb2 partially co-localizes to late endosomal compartments along with AbetaPP and AICD. Increase in the concentration of Grb2 confines it in enlarged late endosomes leading to more sequestration of AbetaPP and AICD within these compartments. This confinement of AbetaPP due to Grb2 overexpression affects its turnover by inhibiting its release via exosomal vesicles. As a consequence, the level of intracellular AbetaPP and AICD increases. The effect of Grb2 overexpression has been verified by knocking down Grb2 as well as by overexpressing Grb2 in Grb2 knocked down cells. Having established the Grb2-mediated trafficking of AICD and its impairment, the significance of its consequence has now become apparent in the downstream events of AD pathogenesis.

AICD and its adaptors - in search of new players.

In view of the emerging evidence that amyloid-beta load in the brain and neuronal deficits are possibly independent events and the increasing importance of downstream molecular cascades in Alzheimer's Disease (AD) pathogenesis, the role of Amyloid Intracellular C-terminal Domain (AICD) is evaluated. This C-terminal fragment of Amyloid-beta protein precursor (AbetaPP) is cytotoxic and is a major component of AD brain. Different portions of AICD bind to different 'adaptors' and are seen to take part in various cellular events including AbetaPP processing and trafficking, apoptosis, neuronal growth and regulation of gene transcription. Phosphorylation also plays an important role in terms of choice of binding partners. The review emphasizes the dynamics of the network created by AICD interactions and points to possible alternative routes of AD like neurodegeneration.