Detection of loss of heterozygosity in the p53 tumor suppressor gene using a PCR-based assay

Vitamin B6 Deficiency Promotes Loss of Heterozygosity (LOH) at the Drosophila warts (wts) Locus

The active form of vitamin B6, pyridoxal 5'-phosphate (PLP), is a cofactor for more than 200 enzymes involved in many metabolic pathways. Moreover, PLP has antioxidant properties and quenches the reactive oxygen species (ROS). Accordingly, PLP deficiency causes chromosome aberrations in Drosophila, yeast, and human cells. In this work, we investigated whether PLP depletion can also cause loss of heterozygosity (LOH) of the tumor suppressor warts (wts) in Drosophila. LOH is usually initiated by DNA breakage in heterozygous cells for a tumor suppressor mutation and can contribute to oncogenesis inducing the loss of the wild-type allele. LOH at the wts locus results in epithelial wts homozygous tumors easily detectable on adult fly cuticle. Here, we found that PLP depletion, induced by two PLP inhibitors, promotes LOH of wts locus producing significant frequencies of wts tumors (~7% vs. 2.3%). In addition, we identified the mitotic recombination as a possible mechanism through which PLP deficiency induces LOH. Moreover, LOH of wts locus, induced by PLP inhibitors, was rescued by PLP supplementation. These data further confirm the role of PLP in genome integrity maintenance and indicate that vitamin B6 deficiency may impact on cancer also by promoting LOH.

Pleomorphic carcinoma of the lung associated with loss of heterozygosity of p53 gene

We report a case with pleomorphic carcinoma of the lung in a 70-year-old man. Pleomorphic carcinoma is characterized by a heterogenous composition that includes epithelial and mesechymal malignancies. In the present case, the tumor was composed of a mixture of unequivocal squamous cell carcinoma and spindle cell components resembling sarcomatous overgrowth. The spindle component did not include a heterologous mesenchymal element characterized by overt differentiation for bone, cartilage, neuron or muscle tissue. To evaluate a state of differentiation of the spindle cell component, we immunohistochemically examined expression of the antigens including vimentin, cytokeratin, sarcomeric actin, alpha-smooth muscle actin, S-100 protein, CD34, Factor VIII, and CD68. The results showed sole expression of vimentin in the spindle cell component, suggesting an immature state of the mesenchymal lineage. Furthermore, the spindle cell component of this case was genetically characterized by loss of heterozygosity (LOH) at a codon 234 of exon 7 of the p53 gene. This mutation causes an amino-acid replacement (Tyr to Cys), which was previously proven to attenuate p53 function. The present case may suggest a relation between somatic alteration of the p53 gene and histogenesis of pleomorphic carcinoma.

Deletion of the p53 gene in a patient with aggressive burn scar carcinoma

BACKGROUND

Aggressive squamous cell carcinoma (SCC) is known to occur in scars that develop after a burn injury, especially in the underdeveloped areas of the world where care is lacking. Because most SCC are associated with abnormalities in tumor suppressor genes, particularly p53, we postulated that similar mechanisms may underlie the development of burn-associated SCC.

METHODS

We analyzed tissue DNA from a patient who died from an aggressive SCC in a burn scar for evidence of p53 gene abnormalities by polymerase chain reaction and immunohistochemical staining for p53 protein.

RESULTS

Using polymerase chain reaction, the p53 gene could not be detected in DNA from the patient's cancer. The p53 protein was also undetectable by immunohistochemical staining.

CONCLUSION

These studies indicate that there was a homozygous deletion of the p53 gene in this burn-related carcinoma. Further studies of other patients may lead to new understanding of this cancer, explain in part the usual aggressive behavior, and lead to new methods of prevention and treatment.