第一型干擾素調節因子在感染性胰臟壞死病毒感染期間參與 磷脂醯絲胺酸受器的活化與促進凋亡細胞清除

Abstract

目前有許多研究顯示病毒的感染會誘發細胞進行凋亡，而有效的清除凋亡細胞對維持正常組織的恆定性(homeostasis)與免疫反應(immune response)的調節相當重要。在凋亡細胞的表面存在一種叫做磷脂醯絲胺酸(phosphatidylserine, PS)標幟物供巨噬細胞或鄰近細胞上的受器(receptor)辨識，以進行對凋亡細胞的吞食(engulfment)，而辨識PS的受器就稱為磷脂醯絲胺酸受器(phosphatidylserine receptor, PSR)。理論上當細胞進行凋亡時,鄰近細胞的PSR表現量應會上升以清除這些凋亡的細胞。至於究竟是什麼因子促使PSR的表現至今仍未明瞭。有研究指出雙股RNA病毒(double strand RNA virus, dsRNA virus)感染會引發第一型干擾素調節因子 (Interferon regulatory factor-1, IRF-1)的大量表現，而此種干擾素調節因子本身是一種轉錄因子(transcription factor)，推測其大量表現可能與其會調控其他抗病毒基因的表現有關，PSR極可能為其中一種抗病毒的基因。 本實驗室之前在魚類細胞的研究發現,大眼鮭胚胎細胞(CHSE-214)在經雙股RNA病毒-傳染性胰臟壞死病毒(infectious pancreatic necrosis virus, IPNV)感染後,會有細胞凋亡的現象發生。然而,凋亡的細胞是否會促進PSR的表現增加,以及IPNV的感染是否會誘發 IRF-1的表現來參與PSR基因的表現調控，這些都是尚待釐清的問題。本實驗目的在於瞭解IPNV在感染鮭魚細胞期間的PSR基因表現情形,以及免疫調控因子IRF-1是否有參與PSR基因的調控而助於凋亡細胞的清除與抑制發炎反應的進行。我們在受感染的細胞中觀察到凋亡的現象,同時PSR以及IRF-1的表現也因為病毒的感染而增加。分析PSR啟動子(promoter)上轉錄因子(transcription factor)的結合位發現,其上確實含有IRF-1的結合位。在加入IRF-1反義核酸(morpholino)抑制IRF-1的表現後發現PSR表現有延遲(delay)的情形發生以及病毒的表現量有增加的趨勢。由此推測鮭魚細胞在IPNV感染後所誘發的PSR表現是極可能是透過IRF-1結合在PSR啟動子上來產生。因此,IPNV感染細胞後會誘發兩條路徑:一條是會走凋亡的路徑,而另一條是藉由雙股RNA所誘發的干擾素(Interferon, IFN)路徑,而後者路徑中的IRF-1會去調控參與凋亡細胞清除的PSR的表現,藉此達到抗病毒的效果。由本實驗的結果發現,PSR的表現是透過IRF-1的調控並同時也會影響病毒的表現量,故PSR在IPNV感染期間確實扮演了清除凋亡細胞的角色而具有抗病毒的效果。

Many researches show that virus infection can induce cell to process apoptosis and it is quite important to do apoptotic cell clearance effectively that can maintain normal tissue homeostasis and regulation of immune response. There is a marker called phosphatidylserine (PS) that can be recognized by a receptor on the macrophage or neighboring cell. The receptor that can recognize PS is called phosphatidylserine receptor (PSR). Theoretically, the PSR expression of neighboring cell beside the apoptotic cell increases to clean the apoptotic cells. However, at present, virus infected how to induce PSR to express still unknown yet. Some researches examined that dsRNA virus infection dramatically can upregulate interferon regulatory factor-1 (IRF-1) as a transcription factor. It presumes that the massive expression of IRF-1 is involved in the regulation of anti-viral genes’ expression which the PSR is one of them. Studies of fish cells in our lab last decade found that double-stranded RNA virus IPNV infection can cause apoptosis in CHSE-214 cells. However, IPNV-induced cell death how to correlate to upregulate the PSR and IRF-1 is still unclear. The purpose of our study is to realize the expression pattern of PSR in salmonid cells during IPNV infection and whether immune regulating factor can participate in PSR gene expression to help the clearance of apoptotic cells and the progressing of anti-inflammation response. We can observe apoptosis in infective cells and both PSR and IRF-1 are increasing with virus infection in the same time. To analyze the transcription factor of PSR promoter constitution, we can find that it contains IRF-1 binding sites. After treating cells with IRF-1 morpholino, the IRF-1 expression is suppressed and the expression pattern of PSR shows delay and the expressing quantity of virus shows increasing trend. Therein, it can assume that the PSR expression in salmonid cells during IPNV infection is through IRF-1 binding on the PSR promoter to activate. Therefore, IPNV infection can induce two pathways; one is apoptosis pathway, and another is to induce interferon pathway by its dsRNA. The IRF-1 of the latter can regulate PSR expression which involving in apoptotic cell clearance to approach anti-viral effects. The results of this study show that PSR expression is through the IRF regulation and it also determines the viral expression quantity. Overall, the PSR actually plays a role for the clearance of apoptotic cells that makes it have a capacity for antiviral effects.