TP53 Codon 72 Polymorphisms and Lung Cancer Risk in the Bangladeshi Population.

OBJECTIVE: To assess associations between codon 72 polymorphisms (Pro or B and Arg or b alleles) of the TP53 gene and lung cancer risk among Bangladeshis. MATERIALS AND METHODS: The distribution of the BB, Bb, and bb genotypes and the frequencies of the B and b alleles were determined by PCR-RFLP method using DNA extracted from leucocytes of 50 confirmed lung cancer patients and 50 age-matched controls and the data were analysed. RESULTS: The ratio of BB, Bb, and bb genotypes were in Hardy-Weinberg equilibrium except for the male patients (χ2=4.6). The B allele is overrepresented among all patients (OR=2.0, p=0.02) and the female patients (OR=4.1, p≤0.01) compared to the controls. The BB/bb ratio was also higher among the patients (OR=3.0, p=0.03). The relative risk of cancer for having BB over bb genotype was 1.8 (p=0.04) but no effect was observed for the Bb genotype. The B allele was overrepresented among patients with adenocarcinomas (OR=2.4, p≤0.01) and squamous cell carcinomas (OR=2.7, p≤0.01) over the controls but the difference was not significant for those with small cell lung carcinomas (OR=1.1, p=0.66). The B allele was overrepresented among patients age 50 or younger (OR=2.7, p≤0.01), but not for older patients (OR=1.7, p=0.07), and among smokers compared to the controls (OR=1.8-10.0, p≤0.01-0.03). However, no correlation between increasing pack-years and lung cancer was observed. CONCLUSIONS: The Pro/Pro (BB) genotype and the B allele are risk factors for lung cancer among Bangladeshis, particularly for people under age 50, women and smokers.

Expression profile and mitochondrial colocalization of Tdp1 in peripheral human tissues.

Tyrosyl-DNA phosphodiesterase 1 (Tdp1) is a DNA repair enzyme that processes blocked 3' ends of DNA breaks. Functional loss of Tdp1 causes spinocerebellar ataxia with axonal neuropathy type 1 (SCAN1). Based on the prominent cytoplasmic expression of Tdp1 in the neurons presumably affected in SCAN1, we hypothesized that Tdp1 participates in the repair of mitochondrial DNA. As a step toward testing this hypothesis, we profiled Tdp1 expression in different human tissues by immunohistochemistry and immunofluorescence respectively and determined whether Tdp1 was expressed in the cytoplasm of tissues other than the neurons. We found that Tdp1 was ubiquitously expressed and present in the cytoplasm of many cell types. Within human skeletal muscle and multiple mouse tissues, Tdp1 partially colocalized with the mitochondria. In cultured human dermal fibroblasts, Tdp1 redistributed to the cytoplasm and partially colocalized with mitochondria following oxidative stress. These studies suggest that one role of cytoplasmic Tdp1 is the repair of mitochondrial DNA lesions arising from oxidative stress.

TDP1 and PARP1 deficiency are cytotoxic to rhabdomyosarcoma cells.

UNLABELLED: Rhabdomyosarcoma is the most common soft tissue sarcoma in children. Metastatic rhabdomyosarcoma in children has a 5-year event-free survival rate of <30%, and a recent clinical trial with irinotecan, a topoisomerase I inhibitor, failed to improve outcome. Therefore, it was surmised that failure of irinotecan may be the result of overexpression of the DNA repair enzyme tyrosyl-DNA phosphodiesterase (TDP1), which processes topoisomerase I-DNA complexes resulting from topoisomerase I inhibitor treatment. Using human tissue microarrays and gene expression arrays, a marked overexpression of TDP1 protein and mRNA in RMS tumors was observed. Critically, knockdown of TDP1 or inhibition of poly(ADP-ribose) polymerase-1 (PARP-1), an enzyme in the same complex as TDP1, sensitized rhabdomyosarcoma cell lines to analogues of irinotecan. Interestingly, BRCA1/2 mutations or altered expression was not detectable in rhabdomyosarcoma cells; however, TDP1 knockdown and PARP-1 inhibition alone were cytotoxic to a subset of rhabdomyosarcoma cells, suggesting that they harbor genetic lesions in DNA repair components that have synthetic lethal interactions with loss of TDP1 or PARP1 function. Furthermore, culturing embryonal rhabdomyosarcoma cells in serum/nutrient-restricted medium increased cellular cytotoxicity upon PARP-1 inhibition and was intrinsically cytotoxic to alveolar, though not embryonal rhabdomyosarcoma cells. The results of these studies suggest a compensatory role for TDP1 in rhabdomyosarcoma after topoisomerase-I based therapy and further demonstrate that TDP1 knockdown, PARP-1 inhibition, and dietary restriction have therapeutic validity. IMPLICATIONS: Selective targeting of TDP1 and/or PARP-1 in rhabdomyosarcoma induces cytotoxicity and sensitizes to DNA damaging agents.