根據過去的研究成果發現，紫外光 (ultraviolet, UV) 是造成皮膚癌的重要危險因子 (risk factor)。照射 UV主要會造成 cyclobutane–pyrimidine dimmers (CPDs) 以及6–4 photoproducts (6–4PPs) 等DNA損害。在台灣，皮膚癌名列十大癌症發生率第九，而與皮膚癌相關功能性蛋白的研究，仍然有許多值得探討的地方，尤其是DNA修補機制 (DNA repair system) 方面，故本研究探討人類人類皮膚表皮細胞株(HaCaT) 以及皮膚基底層癌細胞株 (BCC) 中DNA修補機制與皮膚細胞癌化的相關性。我們利用人類皮膚表皮細胞株 (HaCaT) 以及皮膚基底層癌細胞株 (BCC) ，分析給予UVB後對細胞之生長曲線 (Growth curve) 之影響 ；並以即時定量反轉錄聚合?連鎖反應 (q-PCR) 、微陣列分析 (Microarray) 、西方墨點法 (Western blot) 等，對於HaCaT細胞株與BCC細胞株給予UVB之後，分析在DNA修補機制 (DNA repair system) 的基因表現 (Gene expression) 及蛋白質表現 (Protein expression) 的差異
從UVB 對HaCaT細胞株與BCC細胞株生長影響的實驗結果發現，HaCaT細胞株與BCC細胞株在給予100 mJ/cm2 UVB劑量時，其細胞生長曲線 (Growth curve) 有明顯差異，我們可以得知BCC
細胞株對於UVB的傷害有較高的易感受性。 我們也從不同的DNA修補機制中，篩選了9個DNA修補基因，包括OGG1、MGMT、MPG、TDG、UNG、XPA、XPC、RAD51、XRCC4等。由基因表現及蛋白質表現分析發現，主要與UVB相關之DNA修補機制- base excision repair (BER) ，雖然在BCC細胞株中表現量高於HaCaT細胞株，但在UVB誘導下，HaCaT細胞株中BER的誘導程度遠高於BCC細胞株。我們的實驗結果證明以BER為主的DNA修補機制可能在UVB誘導皮膚癌化的過程 (carcinogenesis) 中，扮演一個重要的角色。
另外，我們的實驗結果也發現，HaCaT細胞株與BCC細胞株若預先照射UVB，可以增加細胞對游離輻射的易感受性，且實驗結果與細胞癌化程度呈現正相關。我們的實驗結果證明，癌細胞若預先照射UVB，只需要約十分之一目前臨床所使用的輻射劑量 (約60 Gy) ，便可以有效抑制癌細胞的生長。 此實驗結果，對未來皮膚癌的臨床治療策略上，可能可以提供一個全新的思考方向。
Exposition of solar ultraviolet (UV) radiation has been identified as one of the major risk factors for skin cancer development in Americans. UV radiation induces two of the most abundant mutagenic and cytotoxic DNA lesions such as cyclobutane–pyrimidine dimmers (CPDs) and 6-4 photoproducts (6-4PPs) and their Dewar valence isomers. However, cells have developed a number of repair mechanisms to counteract the DNA damage caused by UV. Although skin cancer is a common in Taiwan, the pathogenesis is still incompletely studied. In this proposal, we would like to study the role of DNA repair mechanisms in skin tumorgenesis pathway by exposing UV radiation.
Our preliminary results showed that differential susceptibility to UV radiation exposure between a spontaneously immortalized human keratinocyte HaCaT cell line and a human skin basal cell carcinoma (BCC) cell line. We investigated numerous candidate genes in different DNA repair mechanisms affected by UV radiation. Including of OGG1, MGMT, MPG, TDG, UNG, XPA, XPC, RAD51, XRCC4 from different DNA repair mechanisms .Our data indicated that treatment with UVB in HaCaT cells base excision repair (BER) is higher than BCC cells. Similarly results were also observed in mRNA, measured by Real-time polymerase chain reaction (Real-time PCR) method.
Our data suggest that BER may be involved in the development of skin carcinogenesis. Furthermore, UV-B phototherapy maybe is a helpful strategy to skin cancer patients as a pretreatment for radiation therapy. This study is valuable for the understanding the role of functional protein plays in the progression of skin cancer and for the development of new therapeutic modality in the future.
