Aug
12
Mon
2013
Delegate Talk: AIB1 Mediated Modulation of CXCR4-SDF1 Signaling in Breast Cancer @ Acharya Hall
Aug 12 @ 3:23 pm – 3:34 pm
Delegate Talk:  AIB1 Mediated Modulation of CXCR4-SDF1 Signaling in Breast Cancer @ Acharya Hall | Vallikavu | Kerala | India

Binu K Aa, Jem Prabhakarb, Thara Sc and Lakshmi Sd,

aDepartment of Clinical Diagnostics Services and Translational Research, Malabar Cancer Centre, Thalassery, Kerala, India.
bDivision of Surgical Oncology, Division of Pathology
dDivision of Cancer Research, Regional Cancer Centre, Thiruvananthapuram, Kerala, India.


Introduction

AIB1, a member of the nuclear co activators, promotes the transcriptional activity of multiple nuclear receptors such as the ER and other transcription factors. Chemokines produced by stromal cells have potential to influence ERα-positive breast cancer progression to metastasis. CXCR4 is the physiological receptor for SDF1, together shown to stimulate the chemotactic and invasive behavior of breast cancer cells to serve as a homing mechanism to sites of metastasis. We propose that over expression of AIB1 in breast cancer cells leads to increased SDF1 and CXCR4 expression, which induces invasion and metastasis of cancer cells.

Materials and Methods
Breast tumor and normal breast tissues from patients in Regional Cancer Centre, Thiruvananthapuram were used for study. The modulatory effect of AIB1 was studied in MCF-7 cells with AIB1 siRNA transfection along with treatment of 17β-Estradiol (E2), 4-hydroxytamoxifen (4OHT), combinations of E2 and 4OHT. The gene expression pattern and protein localization were assessed by RT-PCR and immunofluorescence microscopy respectively. The metastatic and invasive properties were assessed by wound healing assay. Quantitative colocalization analyses were done to assess the association of proteins using Pearson’s correlation coefficient.

Result and Conclusion
The mRNA and protein level expression of AIB1, CXCR4 and SDF1 were higher in tumor samples than in normal samples. AIB1 was localized to the nuclei whereas CXCR4 and SDF1 immunoreactivity were observed in the cytoplasm and to a lesser extent in the nuclei of tumor epithelial cells. In tumor samples the gene level expressions of AIB1 showed significant positive correlations with SDF1(r = 0.213, p = 0.018). CXCR4 showed significant positive correlation with SDF1 in gene (r = 0.498, p = 0.000) and protein levels(r = 0.375, p = 0.002). Quantitative colocalization analyses showed a marked reduction in expression of CXCR4 and SDF1 in siAIB1MCF-7 cells than MCF-7 cells with different treatment groups. Wound healing assay shows reduced wound healing in siAIB1 treated MCF-7 cells.

In recent years, targeting specific cancer pathways and key molecules to arrest tumor growth and achieve tumor eradication have proven a challenge; due to acquired resistance and homing of cancer cells to various metastatic sites. The present study revealed that silencing AIB1 can prevent the over expression of SDF1 and CXCR4. Co activator levels determine the basal and estrogen-inducible expression of SDF1, a secreted protein that controls breast cancer cell proliferation and invasion through autocrine and paracrine mechanisms (Hall et al. 2003). The effects of CXCR4 overexpression has been correlated with SDF1 mediated activation of downstream signaling via ERK1/2 and p38 MAPK and with an enhancement of ER-mediated gene expression (Rhodes et al. 2011). It is possible that over expression of AIB1 as a stimulant involved in the expression of CXCR4 might up-regulate the expression of prometastatic and angiogenic genes. Thus based on these observations it can be concluded that SDF1/CXCR4 overexpression, with significant association with AIB1 expression, itself contribute to the development of mammary cancer and metastatic progression.

Aug
13
Tue
2013
Invited Talk: Pertubation of DNA topology in mycobacteria @ Acharya Hall
Aug 13 @ 11:50 am – 12:12 pm

NagarajaV. Nagaraja Ph.D.
Professor, Indian Institute of Science, Bengaluru, India


Perturbation of DNA topology in mycobacteria

To maintain the topological homeostasis of the genome in the cell, DNA topoisomerases catalyse DNA cleavage, strand passage and rejoining of the ends. Thus, although they are essential house- keeping enzymes, they are the most vulnerable targets; arrest of the reaction after the first trans-esterification step leads to breaks in DNA and cell death.  Some of the successful antibacterial or anticancer drugs target the step ie arrest the reaction or stabilize the topo -DNA covalent complex. I will describe our efforts in this direction – to target DNA gyrase and also topoisomerase1 from mycobacteria. The latter, although essential, has no inhibitors described so far. The new inhibitors being characterized are also used to probe topoisomerase control of gene expression.

In the biological warfare between the organisms, a diverse set of molecules encoded by invading genomes target the above mentioned most vulnerable step of topoisomerase  reaction, leading to the accumulation of double strand breaks. Bacteria, on their part appear to have developed defense strategies to protect the cells from genomic double strand breaks. I will describe a mechanism involving three distinct gyrase interacting proteins which inhibit the enzyme in vitro. However, in vivo all these topology modulators protect DNA gyrase from poisoning effect by sequestering the enzyme away from DNA.

Next, we have targeted a topology modulator protein, a nucleoid associated protein(NAP) from Mycobacterium tuberculosis to develop small molecule inhibitors by structure based design. Over expression of HU leads to alteration in the nucleoid architecture. The crystal structure of the N-terminal half of HU reveals a cleft that accommodates duplex DNA. Based on the structural feature, we have designed inhibitors which bind to the protein and affect its interaction with DNA, de-compact the nucleoid and inhibit cell growth. Chemical probing with the inhibitors reveal the importance of HU regulon in M.tuberculosis.