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P1.02 - Poster Session 1 - Novel Cancer Genes and Pathways (ID 144)
- Event: WCLC 2013
- Type: Poster Session
- Track: Biology
- Presentations: 1
- Coordinates: 10/28/2013, 09:30 - 16:30, Exhibit Hall, Ground Level
P1.02-008 - hSSB1: an essential regulator of genomic integrity in lung cancer (ID 2045)
09:30 - 16:30 | Author(s): E. Bolderson
Lung cancer remains a leading cause for cancer mortality worldwide. A key feature of lung cancer development is genomic instability resulting from an accumulation of DNA lesions. In normal settings, these DNA lesions, such as double strand breaks and oxidised DNA, are rapidly repaired to prevent cytotoxicity and loss of genetic information. However, the molecular basis for the loss of genome integrity during cancer development remains to be determined. Herein, we have examined the involvement of hSSB1 in maintenance of genome stability and its potential role in lung cancer progression. hSSB1 is a critical component of the repair of DNA double strand breaks. As part of this study, we examined if hSSB1 is also involved in the repair of oxidative stress-induced DNA modifications. The most common nucleotide modification, 8-oxo-7,8-dihydro-guanine (8-oxoG), is repaired by the enzyme OGG1. Failure to repair these modifications results in mismatch mutations which are common in cancer. Therefore, understanding the molecular basis for genomic instability is key to the development of future therapeutics with clinical relevance.
To determine if hSSB1 expression is associated with lung cancer progression, a tissue microarray (TMA) with cores from 550 patients was stained with an anti-hSSB1 antibody. Kaplan-Meier survival curves were generated with the clinical data and patient prognosis was correlated with hSSB1 expression levels. To determine an in vitro association with lung cancer, A549 lung cancer cells were treated with hSSB1 specific siRNA. Cell survival was determined by microscopy and MTT assay. To examine the role of hSSB1 in repair of oxidised DNA, U2OS cells were treated with 500 µM H~2~O~2~. Cells treated with H~2~O~2~ were fixed, stained with antibodies for hSSB1 and 8-oxoG and examined by deconvolution microscopy. Lysates were collected from H~2~O~2~ treated U2OS cells and subjected to immunoprecipitation and Western blot analysis. Genomic DNA isolated from scrambled or hSSB1 siRNA U2OS cells treated with H~2~O~2~ were immobilised on nylon membrane and stained with antibodies for 8-oxoG.
Significantly, TMA staining of lung cancer tissues indicated universal overexpression of hSSB1. Survival curves generated from the patient data indicated a poorer prognosis for patients with increased hSSB1 expression versus lower expressing tumours. Interestingly, in vitro inhibition of hSSB1 using siRNA significantly reduced cell survival. These data highlight the potential prognostic value of hSSB1 expression. As oxidative stress is prevalent in lung cancers, we also tested whether hSSB1 is capable of repairing 8-oxoG DNA lesions. Following oxidative DNA damage, hSSB1 localises rapidly to chromatin. hSSB1 also directly interacts with OGG1 to facilitate OGG1 recruitment to chromatin and repair of DNA damage. Importantly, cells lacking hSSB1 display ineffective repair of 8-oxoGs.
Our data highlight a potential role for hSSB1 in lung cancer progression and a novel role in maintenance of genome integrity. As tumours have increased genomic instability, elevated hSSB1 expression in lung cancer may enable tumours to cope with genomic instability. Taken together, these data present hSSB1 both as a prognostic marker and a novel therapeutic target.