A3 TARGETING PROLINE METABOLISM TO OVERCOME TREATMENT RESISTANCE IN ESOPHAGEAL CANCER

Background

Patients with esophageal malignancy have a 5-year survival rate of only 14% in Canada. This high mortality rate is due to three factors: late diagnosis, difficulty to surgically remove the tumor due to its localization and treatment resistance. Treatment resistance has been ascribed to the presence of cancer stem cells (CSCs) inside the tumor. However, no treatment specifically directed against CSCs is available to patients. Therefore, targeting CSCs is a promising strategy to improve survival of patients with esophageal squamous cell carcinoma (ESCC), the most common type of esophageal cancer worldwide.

Aims

Herein, we developed an unbiased approach to identify new players in chemotherapy and radiotherapy resistance in ESCC.

Methods

We established radioresistant (RR), chemoresistant (CR) and radiochemoresistant (RCR) human ESCC cell lines using weekly radiation and/or continuous treatment with increasing doses of chemotherapeutic agent 5-FU. We validated that the process of resistance acquisition correlates with enrichment in CSCs as revealed by higher ALDH1 expression, and increased proportion of ALDH1^high cells and CD24^high/CD44^high cells in flow cytometry. We then used a proteomic approach to identify new players in treatment resistance.

Results

Interestingly, pathway analysis demonstrated enrichment in energy metabolism as well as amino acid metabolism. Seahorse assays showed a more quiescent metabolism in all three types of resistant cells compared to the control cell line. More precisely, resistant cell lines have a lower respiration rate than control cell line, while glycolysis remains unchanged. Surprisingly, our results show a metabolic rewiring very different from the well-known Warburg effect. To further characterise these metabolic changes, we performed an unbiased metabolomic pilot study and confirmed a decrease in amino acid levels such as proline, in resistant cell lines. Preliminary data show that when cultured in DMEM with proline addition, CD44^high/CD24^high cell proportion is decreased in control and RR cell lines suggesting that proline is a key regulator of CSC population in ESCC.

Conclusions

To conclude, our results suggest an important role of metabolism in ESCC treatment resistance. This study is a first step towards the identification of new targets to fight treatment resistance in ESCC patients.

Funding Agencies

CAG, CIHRCanada research chair TIER 2

A7 FOXL1+ TELOCYTES IN MOUSE COLON ORCHESTRATE ECM BIODYNAMICS AND WOUND REPAIR RESOLUTION

Background

The extracellular matrix (ECM) is a complex assembly of proteins that provide mechanical and biochemical stimuli to the epithelial and mesenchymal cells of the GI mucosa. Deficiencies in ECM assembly, protein production or excessive accumulation can lead to multiples pathologies including fibrosis and cancer. FoxL1+-Telocytes (TCFoxL1+) are subepithelial cells that form a network underneath the epithelium, contributing to the microenvironment that supports epithelial and immune cell homeostasis. We have previously shown that BMPR1A signaling deletion in TCFoxL1+ influences the microenvironment via stromagenesis, immune infiltration and colonic dysplasia in mouse model of GI diseases. However, the precise molecular and mechanical events that contributes to the onset of this state have yet to be elucidated.

Aims

Characterize the modulations in ECM biodynamics induced by BmpR1a-deficient TC FoxL1+ ( BmpR1a△FoxL1+) in mouse colon submucosa.

Methods

Matrisomics was performed to determine the inventory of ECM proteins expressed solely in the GI stromal compartment following tissue deconstruction of control and BmpR1a△FoxL1+ mice colons. Histological and biochemical methods were used to further characterize the collagen network and matrisome-associated modulations. Fluorescence In Situ Hybridization (FISH) was performed to study the bacterial presence in the mucosa.

Results

The set of identified proteins shows an enrichment for proteins involved in collagen network regulation, wound repair homeostasis and immune regulation such as Col1a2, Col3a1, Col6a4 and Coll14a1, as well as SerpinH1, MFAP4, ANXA1 and S100A9. Collagen network is affected with increased deposition and reorganization of fiber alignment. Unfolded collagen content was also increased in dysplastic areas of BmpR1a△FoxL1+ mouse colon with a concomitant increase in the collagen-chaperone SerpinH1. Validations of other targets indicate that BmpR1a△FoxL1+ mice deals with some type of tissue micro-injury and inflammation that is unresolved, creating a unfavorable microenvironment for tissue homeostasis.

Conclusions

Taken together, these results suggest that Bmp-signaling deficient TCFoxL1+ significantly contribute to the collagen network biodynamics through increased collagen deposition, fiber alignment reorganization and regulation of the collagen triple-helix assembly. Other matrisome modulations suggest a state of unresolved wound healing due to tissue injury, that could be the etiology of GI pathology and lead to more severe conditions upon various environmental triggers.

Funding Agencies

CIHR

A40 MATRISOMIC ANALYSIS OF PRE-NEOPLASTIC GASTRIC SUBEPITHELIAL MICROENVIRONMENT FROM SIGNALING-IMPAIRED TELOCYTES MOUSE MODEL

NOT PUBLISHED AT AUTHOR’S REQUEST

Funding Agencies: CIHRScholarship Universite de Sherbrooke FMSS Abdenour-Nabid, MD

A25 THE “UPSIDE-DOWN OR OUTSIDE-IN”: UNDERSTANDING HOW FOXL1+ TELOCYTES GOVERN THE EPITHELIAL-MESENCHYMAL CROSSTALK IMPACTING CELL BEHAVIOR BY USING PROTEOMICS STRATEGIES

Background

The mechanical information contained in the basement membrane (BM) is translated into intracellular signals via a process called mechanotransduction. The integrin-mediated cellular adhesions are found at the center of this outside-in mechanism connecting specific extracellular matrix (ECM) proteins with intracellular adaptors proteins that relay the signal via F-actin cytoskeleton turnover, Rho GTPase activity and eventually down to the nucleus. Dysregulation in any step of this tightly controlled process is a major contributor of disease development. Mesenchymal Foxl1+-telocytes (TCs) are known as a communication hub between stromal and epithelial cells from their proximity to the BM and from their potential roles in epithelial mechanical support and cell signaling. We have shown that BMPR1A signaling deletion in TCs (TCΔBmpr1a) induces stem cell niche defects, stromagenesis and colonic dysplasia in mouse model of GI diseases. Thus far, no study explored TCs relevance in microenvironment biomechanics and its subsequent impact in epithelial mechanotransduction.

Aims

Understand how TCΔBmpr1a can modulate mechanotransduction to induce early dysplastic changes in mouse colon.

Methods

Matrisomics was performed to determine the inventory of ECM proteins expressed solely in the GI stromal compartment following tissue deconstruction of control and TCΔBmpr1a mice colons. Collagen fibers analysis, histological and biochemical methods were used to further characterize the matrix biodynamics. Proteomics of the associated epithelial compartment was also done to expose mechanosensors and signaling cascades affecting cell behaviour.

Results

Matrisomics indicate modulations in fiber assembly proteins (collagens (CL), Decorin, Biglycan), ECM remodelling enzymes (LOXL1, TGM2), growth factors (LTBP1, WNT2B) and cell adhesion mediators (Periostin). This is associated with a reorganization in CL fiber alignment, cellular delocalization of TGM2 and increased unfolded CL content. TCΔBmpr1a leads to shortcomings in matrix assembly, hence variations in the ECM architecture and a novel epithelial mechanotransduction potential. Deregulations in matrix-to-cell communication were shown by proteomic analysis of the epithelial-enriched compartment of colonic dysplastic areas, with modulations of mechanosensors such as focal adhesion components (integrins, paxillin), F-actin cytoskeleton (gelsolin, RhoA) and nuclear lamina (Prelamin A/C, nesprin).

Conclusions

Taken together, these results suggest that TCΔBmpr1a can reprogram epithelial cells by impacting on matrix biodynamics and epithelial mechanotransduction. Modulation in this fine regulated sequence of communication from TCs to the epithelial nucleus via ECM could lead to the etiology of GI pathologies.

Funding Agencies

CIHR

Compartmentalization of regulatory proteins in the cell nucleus

The cell nucleus is increasingly recognized as a spatially organized structure. In this review, the nature and controversies associated with nuclear compartmentalization are discussed. The relationship between nuclear structure and organization of proteins involved in the regulation of RNA polymerase II-transcribed genes is then discussed. Finally, very recent data on the mobility of these proteins within the cell nucleus is considered and their implications for regulation through compartmentalization of proteins and genomic DNA are discussed.

Direct visualization of a protein nuclear architecture

Whether the cell nucleus is organized by an underlying architecture analagous to the cytoskeleton has been a highly contentious issue since the original isolation of a nuclease and salt-resistant nuclear matrix. Despite electron microscopy studies that show that a nuclear architecture can be visualized after fractionation, the necessity to elute chromatin to visualize this structure has hindered general acceptance of a karyoskeleton. Using an analytical electron microscopy method capable of quantitative elemental analysis, electron spectroscopic imaging, we show that the majority of the fine structure within interchromatin regions of the cell nucleus in fixed whole cells is not nucleoprotein. Rather, this fine structure is compositionally similar to known protein-based cellular structures of the cytoplasm. This study is the first demonstration of a protein network in unfractionated and uninfected cells and provides a method for the ultrastructural characterization of the interaction of this protein architecture with chromatin and ribonucleoprotein elements of the cell nucleus.

Mutagenic analysis of human immunodeficiency virus type 1 Vpr: role of a predicted N-terminal alpha-helical structure in Vpr nuclear localization and virion incorporation

The Vpr gene product of human immunodeficiency virus type 1 is a virion-associated protein that is important for efficient viral replication in nondividing cells such as macrophages. At the cellular level, Vpr is primarily localized in the nucleus when expressed in the absence of other viral proteins. Incorporation of Vpr into viral particles requires a determinant within the p6 domain of the Gag precursor polyprotein Pr55gag. In the present study, we have used site-directed mutagenesis to identify a domain(s) of Vpr involved in virion incorporation and nuclear localization. Truncations of the carboxyl (C)-terminal domain, rich in basic residues, resulted in a less stable Vpr protein and in the impairment of both virion incorporation and nuclear localization. However, introduction of individual substitution mutations in this region did not impair Vpr nuclear localization and virion incorporation, suggesting that this region is necessary for the stability and/or optimal protein conformation relevant to these Vpr functions. In contrast, the substitution mutations within the amino (N)-terminal region of Vpr that is predicted to adopt an alpha-helical structure (extending from amino acids 16 to 34) impaired both virion incorporation and nuclear localization, suggesting that this structure may play a pivotal role in modulating both of these biological properties. These results are in agreement with a recent study showing that the introduction of proline residues in this predicted alpha-helical region abolished Vpr virion incorporation, presumably by disrupting this secondary structure (S. Mahalingam, S. A. Khan, R. Murali, M. A. Jabbar, C. E. Monken, R. G. Collman, and A. Srinivasan, Proc. Natl. Acad. Sci. USA 92:3794-3798, 1995). Interestingly, our results show that two Vpr mutants harboring single amino acid substitutions (L to F at position 23 [L23F] and A30F) on the hydrophobic face of the predicted helix coded for relatively stable proteins that retained their ability to translocate to the nucleus but exhibited dramatic reduction in Vpr incorporation, suggesting that this hydrophobic face might mediate protein-protein interactions required for Vpr virion incorporation but not nuclear localization. Furthermore, a single mutation (E25K) located on the hydrophilic face of this predicted alpha-helical structure affected not only virion incorporation but also nuclear localization of Vpr. The differential impairment of Vpr nuclear localization and virion incorporation by mutations in the predicted N-terminal alpha-helical region suggests that this region of Vpr plays a role in both of these biological functions of Vpr.

Degradation of CD4 induced by human immunodeficiency virus type 1 Vpu protein: a predicted alpha-helix structure in the proximal cytoplasmic region of CD4 contributes to Vpu sensitivity

The HIV-1-encoded Vpu protein induces a rapid and specific degradation of CD4 molecules in the endoplasmic reticulum (ER). In this study, Vpu-induced degradation of CD4 in the ER was investigated by quantitative immunoprecipitation of CD4 following cotransfection of COS-7 cells with CD4 and Vpu expressors in the presence of brefeldin A, a drug that blocks protein transport from the ER to the Golgi complex. In order to precisely define the sequence(s) or structural element(s) in the CD4 cytoplasmic domain necessary for Vpu-induced degradation, a panel of deletion and substitution mutants in the cytoplasmic domain of CD4 was generated and analyzed. In agreement with previous reports, our deletion analysis indicates that a region encompassing amino acids 411 to 419 (KRLLSEKKT) in the cytoplasmic domain of CD4 was required to confer Vpu sensitivity. However, six specific substitution mutations within this region did not confer CD4 resistance to Vpu, suggesting that neither the amino acid sequence nor the charge of the amino acids in this region was critical to Vpu-induced CD4 degradation. A dileucine motif that is important for internalization of CD4 and Nef-induced CD4 down-regulation was also not required for Vpu-induced CD4 degradation. Interestingly, two substitution mutants (CD4EMKL and CD4MK407,11PP) located in a more proximal cytoplasmic region of CD4 abolished Vpu-induced CD4 degradation. Computer-assisted analysis of the substitution and deletion mutants conferring CD4 resistance to Vpu-induced degradation indicated that these mutations disrupted a putative alpha-helix formed in the proximal cytoplasmic region of CD4. Taken together, these studies strongly suggest that a structural element in the proximal cytoplasmic region of CD4 contributes to Vpu sensitivity.

Mutational analysis of the HIV-1 Vpu protein

The human immunodeficiency virus type-1 (HIV-1) encoded Vpu protein facilitates the release of budding virions from the surface of infected cells and delays the rate of syncytium formation of the virus. Furthermore, Vpu induces rapid degradation of nascent CD4 molecules that are retained in the endoplasmic reticulum by the formation of gp160-CD4 complexes. Currently, little is known of the precise mechanism(s) by which Vpu function. Whether or not these different events are related remain unclear. In this report, we describe our recent structure/function studies on vpu suggesting that the protein may have independent biological activities during the HIV-1 infection.

The effect of vpu on HIV-1-induced syncytia formation

To investigate the role of vpu in the cytopathicity of human immunodeficiency type 1 (HIV-1), the MT4 CD4+ T-cell line was infected with viruses that were isogenic except for their ability to produce the vpu protein. The experiments described here demonstrate that expression of vpu reduces HIV-1 cytopathic effects by decreasing the rate of syncytia formation. By reducing the concentration of gp 120 at the cell surface, vpu limits cell killing by syncytia formation.

alpha-1-Antitrypsin phenotypes in French Canadian newborns

Cord blood sera from 390 French Canadian babies born consecutively in a Montreal hospital were phenotyped for alpha 1-antitrypsin. As in other populations, Pi M was the most frequent allele. The second most frequent was Pi S (0.0923). This Pi S allele frequency is significantly different from that of other Canadians, but similar to that of Normans and Bretons.

Difference in the distribution of e antigen among different ethnic groups in a population of blood donors

Sensitive techniques were used to detect e antigen and the corresponding antibody (anti-e) among 368 voluntary blood donors positive for hepatitis B surface antigen in the Montreal area and 310 people living in close contact with them. Neither e nor anti-e was found in the absence of markers of hepatitis B virus (HBV). Among the blood donors e antigen was detected in 23 and anti-e in 313, and 32 were negative for both markers. Of the 368 blood donors 330 were of French origin and 38 from other ethnic groups. The 23 e-positive subjects were unequally distributed among the ethnic groups: only 14 (4.2%) were recruited among the French group while 9 (23.7%) were recruited among other ethnic groups (P less than 0.001). This differences among ethnic groups might be related to the vertical or horizontal mode of dissemination of HBV infection.