CD45分子在HIV-1病毒感染中的作用研究進展

李克雷，薛 婧，魏 強

(北京協和醫學院比較醫學中心，中國醫學科學院醫學實驗動物研究所，衛生部人類疾病比較醫學重點實驗室，國家中醫藥管理局人類疾病動物模型三級實驗室，新發再發傳染病動物模型研究北京市重點實驗室，北京 100021)

CD45分子在HIV-1病毒感染中的作用研究進展

李克雷，薛 婧，魏 強

(北京協和醫學院比較醫學中心，中國醫學科學院醫學實驗動物研究所，衛生部人類疾病比較醫學重點實驗室，國家中醫藥管理局人類疾病動物模型三級實驗室，新發再發傳染病動物模型研究北京市重點實驗室，北京 100021)

CD45分子是具有磷酸酶活性的跨膜蛋白，在免疫細胞中發揮重要作用。CD45分子對抗原受體信號轉導是必需的，并具有調節細胞凋亡的作用，其功能紊亂會導致自身免疫性疾病、免疫缺陷、惡性腫瘤等。CD45分子的結構及其功能與HIV感染之間的關系是艾滋病研究領域的重要內容之一，本文就CD45分子在HIV感染中的作用作一綜述。

CD45；HIV；免疫細胞

CD45分子是受體蛋白酪氨酸磷酸酶，主要表達于有核的造血細胞，主要功能涉及造血細胞的發育、活化、衰老和凋亡。CD45對T細胞的發育非常重要，如果CD45丟失，那么在胸腺中進行的雙陽性選擇會導致細胞的大量凋亡。此外，CD45作為跨膜分子，在細胞的信號轉導中發揮重要作用。鑒于CD45是細胞膜上信號轉導的關鍵分子，在淋巴細胞的發育成熟、功能調節及信號傳遞中具有重要意義。

1 CD45分子的結構

CD45分子為I型跨膜糖蛋白，其胞內區由D1、D2兩個結構域組成，D1結構域具有酪氨酸磷酸酶活性，D2結構域對D1結構域的活性起調節作用；其胞外區包括3個纖維連接蛋白區、1個半胱氨酸富集區和3個由mRNA的選擇性剪接得到的結構域，即A、B、C異構體。成熟的CD45分子量范圍為180—240 kDa，其最大的異構體為CD45RABC，最小的變構體為CD45RO，結構如圖1所示[1]。CD45RABC富含O-聚糖和N-聚糖，主要包括A、B、C 3個含O-聚糖的區域，近膜端區域含有N-聚糖；另一種剪接形式CD45RO僅含有N-聚糖的近膜端區域，不含有O-聚糖。

CD45分子上的O-聚糖主要包括兩個核心結構：core-1與core-2[2]，這兩個核心結構可被聚N-乙?；?、唾液酸和海藻糖修飾。與O-聚糖不同，N-聚糖前體合成時具有甘露糖結構，以便其在高爾基體內修飾，N-聚糖的這種結構增加了CD45的穩定性。糖基化形式在細胞表面的變化對細胞存活及功能具有重要影響。

圖1 CD45分子結構示意圖 [19]Fig.1 Schematic diagram of the molecular structure of CD45

2 CD45分子在免疫細胞中的作用

CD45分子是T細胞活化所必需的。研究表明TCR或CD3信號刺激不能使CD45表達缺失的T細胞增殖和產生細胞因子[3、4]，并且在CD45缺陷的小鼠模型中也證明CD45在免疫系統中發揮的重要作用[5、6]。

CD45分子主要是通過蛋白酪氨酸激酶(PTKs)的調節來實現對淋巴細胞的發育和活化的調控[7]。PTKs由Src家族(p56lck和p59fyn)、Syr家族(ZAP-70)和Jak家族組成，CD45對p56lck和p59fyn的調節在淋巴細胞活化和信號轉導中起重要作用。p56lck和p59fyn分子結構上存在兩個關鍵的調節性酪氨酸磷酸化位點，即一個活化位點和一個抑制位點。CD45通過使活化位點和抑制位點去磷酸化控制Src激酶的活性[8]。在靜息淋巴細胞中，CD45可以和磷酸基團競爭抑制位點并使活化位點去磷酸化，使Src激酶處于非活化狀態。當抗原和受體結合后，膜蛋白的位置發生改變，Src激酶向抗原受體方向位移，使Src激酶和CD45分離，活化位點磷酸化而使Src激酶活化，此時CD45發揮正向調節作用。在整合素介導的細胞粘附過程中，Src激酶和CD45同時向粘附位點位移，活化位點去磷酸化，此時CD45發揮負調節作用[9、10]。

在淋巴T細胞的分化過程中，CD45表達不同的異構體，同時細胞表面的糖基化也發生改變。T細胞表面的糖基化形式可用來區分T細胞亞群[11]，花生凝集素可與無唾液酸化的core-1O-聚糖結合，而不能與唾液酸化core-1O-聚糖結合，而兩者在不同細胞上存在，前者存在于活化T細胞，后者存在于初始T細胞。Core-2O-聚糖存在于不成熟的胸腺細胞，而不存在于成熟的胸腺細胞，也存在于活化的T細胞而非初始T細胞[12、13]。CD45糖基化對細胞的功能及存活可產生重要影響。CD45糖基化可調節T細胞的細胞因子產生[14]，凝集素jacalin可通過特異地與CD45 core-1O-聚糖末端的Galβ1-3GalNAc結合而活化T細胞，并誘導T細胞產生IL-2。Galectin-1也可通過與CD45的結合調節細胞因子的產生，減少Th1的細胞因子水平，增加Th2細胞因子的產生能力[15、16]；CD45糖基化對調節細胞凋亡的易感性，galectin-1結合CD45誘導T細胞凋亡，只有當T細胞共表達C2GnT和CD45的core-2O-聚糖時，galectin-1才能誘導凋亡[17、18]。Galectin-3也可誘導T細胞凋亡，而這一過程受到CD45分子O-聚糖和N-聚糖的調節，galectin-3能誘導CD45+Jurkat細胞調亡，但不能誘導CD45-J45.01細胞凋亡，galectin-3僅能誘導CD45RABC-J45.01細胞發生凋亡卻不能誘導CD45RO-J45.01細胞發生凋亡，表明CD45分子中的O-聚糖在調節galectin-3誘導Jurkat細胞調亡中發揮著重要的作用[19]。

3 CD45在HIV感染中的作用

T細胞是HIV感染的主要靶細胞。在HIV感染時，對T細胞表面分子的變化研究能夠進一步闡述HIV的感染機制。研究表明，表達CD45RO的CD4+T細胞更易于結合HIV-1，而CD45RO-細胞卻不能結合[20、21]，并且與HIV在CD4+CD45RABC+初始細胞內復制程度相比，HIV更容易在CD4+CD45RO+記憶細胞內復制[22]，當HIV感染CD4+CD45RO+細胞時，CD3/CD28刺激信號引起的細胞核因子反應更強烈，進一步說明HIV在CD45RO+細胞內更易復制[23]。學者還發現HIV感染時CD45在T細胞表面的密度減少，CD4+T細胞上CD45RA和CD45RO表達降低，CD45RA在CD8+T細胞上降低，CD45RO在CD8+T細胞的表達升高[24、25]，由于CD45基因的多樣性，使得表達不同CD45分子的細胞對病毒的易感性有很大差異。例如將編碼CD45的外顯子進行C77G突變后，CD45的mRNA會發生異常剪切，最終可增加細胞對HIV的易感性[26]；其他研究也顯示CD45的多態性與細胞對HIV的易感性有關，在非洲烏干達人中CD45的第4個外顯子有A54G突變，而這種的突變結構降低了HIV的感染頻率[27]，這些都證明CD45與HIV感染密切相關。

HIV感染T細胞后可使細胞發生凋亡，多種機制參與了這一過程，其中包括CD45分子介導的細胞凋亡。由于HIV-1感染T細胞可干擾CD45的酪氨酸磷酸酶活性和PLCγ的功能，對CD45活性的這種影響與疾病進程和細胞凋亡相關[28、29]。HIV的Tat、Vpr、Nef、gp120蛋白都可誘導細胞凋亡[30-33]，但在對gp120誘導凋亡的研究中發現，gp120通過活化誘導的凋亡涉及到了細胞的活化[30，34]，由于CD45分子在細胞活化過程中發揮重要作用，那么gp120誘導的凋亡可能與CD45有關。研究表明gp120誘導CD45-的T細胞凋亡率顯著降低，CD45對gp120誘導凋亡的是通過抑制PI3K/Akt途徑誘導FasL表達實現的，這表明CD45的胞外區在調節細胞凋亡過程中發揮作用[35]，由于CD45胞外區具有多種糖基化位點，推測CD45的糖基化也在調節gp120誘導的凋亡過程中發揮作用。研究顯示在HIV感染機體的過程中，一些未感染的T細胞的CD45的糖基化修飾發生變化，即無唾液酸化core-1O-聚糖和core-2O-聚糖表達增加，由于這種變化使得這些未感染細胞而通過旁觀者效應發生凋亡[36]。

由于HIV潛伏庫的存在，當前的AIDS治療方法并不能有效完全清楚體能的HIV病毒，而潛伏感染的CD4+T是HIV治療的主要障礙[37]。HIV主要潛伏在靜息的記憶T細胞中[38]，靜息記憶T細胞表面標志為CD4+CD45RO+，故對CD45分子的深入研究可能為清除HIV潛伏庫提供新的思路。研究表明，在豬尾獼猴體內，表達于CD4+T細胞表面的CD45RO 可用于檢測HIV-1 感染模型中潛伏庫細胞的數量[39]，并且也有學者采用抗CD45RO的免疫毒素來清除HIV潛伏庫細胞，在體外，該免疫毒素清除潛伏感染細胞效率可達到99%，且對CD45RA+初始T細胞和CD8+記憶T細胞無殺傷作用[40、41]，表明針對CD45RO的靶向藥物設計具有清除HIV潛伏庫的可行性。

4 展望

CD45是一個重要的跨膜分子，它以其蛋白酪氨酸磷酸酶活性使蛋白酪氨酸激酶的抑制位點的酪氨酸去磷酸化從而使其活化，進而在T細胞活化的信號傳遞中起重要作用。隨著對CD45研究的深入，發現CD45與多種疾病相關，人們試圖利用單克隆抗體或藥物阻斷CD45介導的信號轉導來阻斷淋巴細胞的活化，進而應用于誘導免疫耐受和逆轉移植排斥反應的研究。但CD45及其結合蛋白在淋巴細胞的發育、增殖和活化過程中的確切作用機制仍不甚清楚，特別是CD45分子在HIV感染過程中的作用以及對潛伏庫細胞形成的作用仍需進一步研究。

[1] Dupéré-Minier G, Desharnais P, Bernier J. Involvement of tyrosine phosphatase CD45 in apoptosis [J]. Apoptosis, 2009, 15(1): 1-13.

[2] Furukawa K, Funakoshi Y, Autero M, et al. Structural study of the O-linked sugar chains of human leukocyte tyrosine phosphatase CD45 [J]. Eur J Biochem, 1998, 251(1-2): 288-294.

[3] Pingel JT, Thomas ML. Evidence that the leukocyte-common antigen is required for antigen-induced T lymphocyte proliferation [J]. Cell, 1989, 58(6): 1055-1065.

[4] Koretzky GA, PicusJ, Schultz T, et al. Tyrosine phosphatase CD45 is required for T-cell antigen receptor and CD2-mediated activation of a protein tyrosine kinase and interleukin 2 production [J]. Proc Natl Acad Sci U S A, 1991, 88(6): 2037-2041.

[5] Kishihara K, Penninger J, Wallace VA, et al. Normal B lymphocyte development but impaired T cell maturation in CD45-exon6 protein tyrosine phosphatase-deficient mice.[J]. Cell, 1993, 74(74): 143-156.

[6] Byth KF, Conroy LA, Howlett S, et al. CD45-null transgenic mice reveal a positive regulatory role for CD45 in early thymocyte development, in the selection of CD4+CD8+ thymocytes, and B cell maturation [J]. J Experimenta Med, 2015, 68(1): 105-114.

[7] Penninger JM, Irie-Sasaki J, Sasaki T, et al. CD45: New jobs for an old acquaintance [J]. Nature Immunol, 2001, 2(5): 389-96.

[8] Roach T, Slater S, Koval M, et al. CD45 regulates Src family member kinase activity associated with macrophage integrin-mediated adhesion [J]. Curr Biol, 1997, 7(6): 408-417.

[9] Thomas ML, Brown EJ. Positive and negative regulation of Src-family membrane kinases by CD45 [J]. Immunol Today, 1999, 20(20): 406-411.

[10] Alexander DR. The CD45 tyrosine phosphatase: a positive and negative regulator of immune cell function [J]. Semin Immunol, 2000, 12(4): 349-359.

[11] ReisnerY, Linker-Israeli M, Sharon N. Separation of mouse thymocytes into two subpopulations by the use of peanut agglutinin [J]. Cell Immunol, 2005, 314(7086): 1033-1036.

[12] Galvan M, Murali-Krishna K, Ming LL, et al. Alterations in cell surface carbohydrates on T cells from infected mice can distinguish effector/memory CD8+ T cells from naive cells [J]. J Immunol, 1998, 161(2): 641-648.

[13] Grabie N, Delfs MW, Lim YC, et al. β-Galactoside α2,3-sialyltransferase-I gene expression during Th2 but not Th1 differentiation: implications for core2-glycan formation on cell surface proteins [J]. Eur J Immunol, 2002, 32(10): 2766-2772.

[14] Makoto B, Bruce YM, Motohiro N, et al. Glycosylation-dependent interaction of Jacalin with CD45 induces T lymphocyte activation and Th1/Th2 cytokine secretion [J]. J Leukocyte Biol, 2007, 81(4): 1002-1011.

[15] Cedenolaurent F, Opperman M, Barthel SR, et al. Galectin-1 triggers an immunoregulatory signature in T helper cells functionally defined by il-10 expression[J].J Immunol, 2012,188(7): 3127.

[16] Baum LG, Blackall DP, Sarah AM, et al. Amelioration of graft versus host disease by galectin-1 [J]. Clin Immunol, 2003, 109(3): 295-307.

[17] Nguyen JT, Evans DP, Galvan M, et al. CD45 modulates galectin-1-induced T cell death: regulation by expression of core 2 O-glycans [J]. J Immunol, 2001, 167(10): 5697-707.

[18] Galvan M, Tsuboi S, Fukuda M, et al. Expression of a specific glycosyltransferase enzyme regulates T cell death mediated by galectin-1 [J]. J Biol Chem, 2000, 275(22): 16730-16737.

[19] Jing X, Xiqiang G, Chunyan F, et al. Regulation of galectin-3-induced apoptosis of Jurkat cells by both O-glycans and N-glycans on CD45 [J]. FEBS Letters, 2013, 587(24): 3986-3994.

[20] Julià B, Jordi B, Arantxa G, et al. Preferential attachment of HIV particles to activated and CD45RO+CD4+T cells [J]. AIDS Res Human Retroviruses, 2002, 18(1): 27-38.

[21] WangWF, Guo J, Yu DY, et al. A dichotomy in cortical actin and chemotactic actin activity between human memory and naive T cells contributes to their differential susceptibility to HIV-1 infection [J]. J Biol Chem, 2012, 287(42): 35455-35469

[22] Spina CA, Prince HE, Richman DD. Preferential replication of HIV-1 in the CD45RO memory cell subset of primary CD4 lymphocytes in vitro [J]. J Clin Invest, 1997, 99(7): 1774-1785

[23] Robichaud G A, Benoit B, Jean-Francois F, et al. Nuclear factor of activated T cells is a driving force for preferential productive HIV-1 infection of CD45RO-expressing CD4+ T cells [J]. J Biol Chem, 2002, 277(26): 23733-13741.

[24] Mahalingam M, Pozniak A, Mcmanus T J, et al. Abnormalities of CD45 isoform expression in HIV infection [J]. Clin Immunol Immunopathol, 1996, 81(2): 210-214.

[25] Bruunsgaard H, Pedersen C, Scheibel E, et al. Increase in percentage of CD45RO+/CD8+ cells is associated with previous severe primary HIV infection [J]. J Acquired Immune Defic Syndr Human Retrovirol, 1995, 10(2): 107-114.

[26] Tchilian EZ, Wallace DL, Dawes R, et al. A point mutation in CD45 may be associated with an increased risk of HIV-1 infection [J]. AIDS, 2001, 15(15): 1892-1894

[27] Stanton T, Boxall S, Bennett A, et al. CD45 variant alleles: possibly increased frequency of a novel exon 4 CD45 polymorphism in HIV seropositive Ugandans [J]. Immunogenetics, 2004, 56(2): 107-110.

[28] Giovannetti A, Pierdominici M, Mazzetta F, et al. HIV type 1-induced inhibition of CD45 tyrosine phosphatase activity correlates with disease progression and apoptosis, but not with anti-CD3-induced T cell proliferation [J]. AIDS Res Human Retroviruses, 2000, 16(3): 211-219.

[29] Guntermann C, Amft N, Murphy BJ, et al. Impaired CD45-associated tyrosine phosphatase activity during HIV-1 infection: implications for CD3 and CD4 receptor signaling [J]. Biochemical Biophys Res Commun, 1998, 252(1): 69-77.

[30] Roggero R, Robert-Hebmann V, Harrington S, et al. Binding of human immunodeficiency virus type 1 gp120 to CXCR4 induces mitochondrial transmembrane depolarization and cytochrome c-mediated apoptosis independently of Fas signaling [J]. J Virol, 2001, 75(16): 7637-7650.

[31] Lenassi M, Cagney G, Liao M, et al. HIV Nef is secreted in exosomes and triggers apoptosis in bystander CD4+ T cells [J]. Traffic 2010, 11, 110-122.

[32] Nayoung K, Sami K, Sumeet G, et al. Association of Tat with promoters of PTEN and PP2A subunits is key to transcriptional activation of apoptotic pathways in HIV-infected CD4+ T cells [J]. Plos Pathogens, 2010, 6(9): e1001103-e1001103.

[33] Arokium H, Kamata M, Chen I. Virion-associated Vpr of human immunodeficiency virus type 1 triggers activation of apoptotic events and enhances Fas-induced apoptosis in human T cells [J]. J Virol, 2009, 83(21): 11283-11297.

[34] Westendorp MO, Frank R, Ochsenbauer C, et al. Sensitization of T cells to CD95-mediated apoptosis by HIV-1 Tat and gp120 [J]. Nature, 1995, 375(6531): 497-500.

[35] Anand AR, Ganju RK. HIV-1 gp120-mediated apoptosis of T cells is regulated by the membrane tyrosine phosphatase CD45[J]. J Biol Chem, 2006, 281(18): 12289-12299.

[36] Lantéri M, Giordanengo V, Hiraoka N, et al. Altered T cell surface glycosylation in HIV-1 infection results in increased susceptibility to galectin-1-induced cell death [J]. Glycobiology 2003, 13: 909-918.

[37] Dahabieh MS, Battivelli E, Verdin E. Understanding HIV latency: The road to an HIV cure [J]. Ann Rev Med, 2015, 66: 407-421.

[38] Angela C, Pejman M, Monica G, et al. Bioinformatics and HIV latency [J]. Curr HIV/AIDS Rep, 2015, 12(1): 97-106.

[39] Valentine M, Song K, Maresh GA, et al. Expression of the memory marker CD45RO on helper T cells in macaques [J]. PLoS One, 2013, 8(9): e73969.

[40] Mccoig C, Dyke GV, Chou CS, et al. An anti-CD45RO immunotoxin eliminates T cells latently infected with HIV-1 in vitro [J]. Proc Natl Acad Sci U S A, 1999, 96(20): 11482-11485.

[41] Saavedra-Lozano J, Cao Y, Callison J, et al. An anti-CD45RO immunotoxin kills HIV-latently infected cells from individuals on HAART with little effect on CD8 memory [J]. Proc Natl Acad Sci U S A, 2004, 101(8): 2494-2499.

Research progress on the role of CD45 in HIV-1 infection

LI Ke-lei，XUE Jing，WEI Qiang

(Comparative Medicine Center, Peking Union College (PUMC) & Institute of Laboratory Animal Science, Chinese Academy of Medical Sciences (CAMS); Key Laboratory of Human Diseases Comparative Medicine, Ministry of Health; Key Laboratory of Human Diseases Animal Models, State Administration of Traditional Chinese Medicine, Beijing Key Laboratory for Animal Models of Emerging and Re-emerging Infectious Diseases, Beijing 100021, China)

CD45 is a transmembrane molecule with phosphatase activity, and plays a major role in immune cells. CD45 is required for the antigen receptor signal transduction, and attributed as an apoptosis regulator. Impairment of this function may result in autoimmune, immunodeficiency, and malignant diseases. The role of CD45 in HIV-1 infection is one of important research topics. This paper summarizes the research progress on the role of CD45 in HIV-1 infection.

CD45；HIV-1；Immune cells

國家自然科學基金(青年科學基金項目，81301437)，科技部重大專項(2014ZX10001001-001-004，2014ZX10001001-002-006)。

李克雷(1986-)，男，博士生，從事實驗動物病毒學和免疫學工作。E-mail： leekelei@126.com。

魏強，教授，博士導師，研究方向：實驗動物病毒學。E-mail： weiqiang@cnilas.pumc.edu.cn。

綜述與專論

R-33

A

1671-7856(2017) 06-0082-04

10.3969.j.issn.1671-7856. 2017.06.017

2017-02-21