猴病毒四十型T/t-common蛋白質特異性地誘導HER2/neu大量表現的癌細胞走向細胞凋亡

Abstract

HER2/neu屬於表皮生長因子接受器家族(epidermal growth factor receptor family；EGF receptor family)的一員。HER2/neu基因在許多人類癌症中時常有放大(amplification)或過度表現(overexpression)的現象，目前已知HER2/neu可以傳遞數個不同的信號路徑，這些路徑導致HER2/neu具有強大的致癌能力，因此，HER2/neu被認為是治療癌症的標的之一。 我們實驗室之前的研究證實了，SV40 T/t-common可以抑制HER2/neu啟動子的活性，並且可以抑制HER2/neu-overexpressing的卵巢癌細胞SK-OV-3中HER2/neu的表現量及其轉形活性。 在本論文中，我們進一步發現，T/t-common可以專一性的造成HER2/neu-overexpressing的癌細胞走向細胞凋亡，但是卻不會影響HER2/neu low-expressing的癌細胞或非轉形細胞。而T/t-common造成HER2/neu-overexpressing的癌細胞走向細胞凋亡，可能是透過抑制HER2/neu的表現，影響了細胞內MEK-ERK訊息傳遞，造成Bcl-2及Bcl-XL表現量下降，而導致細胞走向細胞凋亡。另外，我們也發現，T/t-common可以專一性的抑制HER2/neu-overexpressing的癌細胞在柔軟瓊脂產生聚落的能力，T/t-common亦具有抑制新生血管形成的潛力。以上結果顯示，T/t-common具有用於治療HER2/neu-overexpressing癌症的潛力。同時在本論文中，增加細胞中p300的表現量，仍然無法回復被T/t-common所抑制的HER2/neu啟動子的活性，因此，T/t-common並不是透過抑制p300而抑制了HER2/neu啟動子的活性。

HER2/neu gene (also known as erbB-2) is a proto-oncogene which belongs to the epidermal growth factor receptor family. It is overexpressed in many human cancers, including breast, lung, ovary, pancreas, gastric, and oral cancers. Overexpression of HER2/neu is associated with poor clinical outcome, including short survival time and short time to relapse. HER2/neu-overexpressing cancer cells usually have higher potential to proliferate, metastasize, induce angiogenesis, and resist chemotherapeutic agents. Inhibition of HER2/neu can lead to suppression of the tumorigenicity of HER2/neu-overexpressing cancer cells. Therefore HER2/neu gene is a suitable target for cancer treatment. Previously we reported that simian virus 40 (SV40) T/t-common polypeptide, which contains the N-terminal common domain of SV40 large T and small t antigens, can repress HER2/neu expression and consequently suppress the tumorigenic potential of the HER2/neu-overexpressing ovarian carcinoma cells. Here we report that T/t-common could specifically induce apoptosis in HER2/neu-overexpressing human cancer cell lines but not in non-transformed cell lines and HER2/neu low-expressing human cancer cell lines. T/t-common’s ability to induce apoptosis in HER2/neu-overexpressing cancer cells was derived from its ability to inhibit HER2/neu, because re-expression of a large amount of HER2/neu could block apoptosis induced by T/t-common. T/t-common expression in HER2/neu-overexpressing SK-OV-3 cancer cells led to down-regulation of Bcl-2 and Bcl-XL, and overexpression of Bcl-2 could inhibit T/t-common’s ability to induce apoptosis in these cells. Therefore, T/t-common’s apoptosis-inducing activity is related to its ability to inhibit Bcl-2 expression in HER2/neu-overexpressing cancer cells. Consistent with T/t-common’s apoptosis-inducing activity, we found that T/t-common could specifically inhibit the soft-agarose colony-forming ability of the HER2/neu-overexpressing human cancer cell lines but not that of the HER2/neu low-expressing human cancer cell lines. Finally, we demonstrated that T/t-common could specifically sensitize HER2/neu-overexpressing human cancer cell lines, but not HER2/neu low-expressing human cancer cell lines, to chemotherapeutic agent etoposide. Together, these data suggest that T/t-common alone or in combination with chemotherapy may provide a new approach for treatment of cancers that overexpress HER2/neu.