Expression of DNA Double Stranded Break Repair Proteins in Melanoma
JA Brown, WL Cheung. University of Arkansas for Medical Sciences, Little Rock, AR
Background: UV (ultraviolet) radiation has been linked to increased risk of skin cancer including melanoma. However, the mechanism of UV radiation in carcinogenesis is still unclear. A viable hypothesis is the accumulation of damaged DNA by way of UV radiation, leading to DNA double stranded breaks (DSB). When the DSB load has reached an irreparable sum, the cells activate the pathway of cell death or apoptosis. Previously, we determined that DNA DSBs, as detected by histone H2AX phosphorylation, are increased in human melanoma tissue. Hence, we aim to determine if the downstream effector of DNA DSB, namely the DNA repair proteins, are recruited/overexpressed in melanoma cells as well. Examination of the proteins; MDC1 (mediator of DNA damage checkpoint protein), RAD50, 53BP1 (p53 binding protein 1) and NBS1 (Nijmegen breakage syndrome protein 1), responsible for the initial steps of DSB DNA damage repair should provide insight to the questions proposed.
Design: For this preliminary study, 15 cases of each of the following lesions have been retrieved from our archives: invasive melanoma, melanoma in-situ, dysplastic melanocytic nevi and congenital nevi. Commercially available antibodies specific for MDC1, RAD50, 53BP1, and NBS1 will be employed. Routine immunohistochemical stainings are performed. The results will be interpreted by relying both on the quantitative and qualitative value of positive staining patterns in the nucleus.
Results: Although we are still in the process of analyzing the results, we have already noticed that some the the DNA damage repair proteins such as NBS1 are overexpressed in many of the melanoma while others are decreased.
Conclusions: This is the first known systematic study to determine whether the DNA damage repair pathway is activated in human melanoma cells. Previous studies from our group and others have recognized that histone H2AX phosphorylation, which is associated with DNA DSB, is enhanced in melanoma cells. Increases in DNA DSB suggest that the breaks are either not being repair properly or that the breaks are being repaired but the histone signaling is defective. In the context of these results, pursuit and determination of whether the initial steps in the DNA damage repair pathway are defective is underway. Our preliminary results suggest that at least one of the DNA damage repair proteins is not localizing to the nucleus; therefore, supporting the idea that the increase in DNA DSB may be due to a defective DNA DSB repair protein. A larger study is currently being performed to further validate this result.
Wednesday, March 24, 2010 1:00 PM
Poster Session VI # 83, Wednesday Afternoon