Department of Microbiology and Immunology, SUNY Upstate Medical University, Syracuse, New York, USA.
Department of Microbiology and Immunology, SUNY Upstate Medical University, Syracuse, New York, USA
J Virol. 2020 Jul 30;94(16). doi: 10.1128/JVI.00167-20.
Human cytomegalovirus (HCMV) is a major cause of morbidity and mortality among immunocompromised and immunonaive individuals. HCMV-induced signaling initiated during viral entry stimulates a rapid noncanonical activation of Akt to drive the differentiation of short-lived monocytes into long-lived macrophages, which is essential for viral dissemination and persistence. We found that HCMV glycoproteins gB and gH directly bind and activate cellular epidermal growth factor receptor (EGFR) and integrin β1, respectively, to reshape canonical Akt signaling within monocytes. The remodeling of the Akt signaling network was due to the recruitment of nontraditional Akt activators to either the gB- or gH-generated receptor signaling complexes. Phosphoinositide 3-kinase (PI3K) comprised of the p110β catalytic subunit was recruited to the gB/EGFR complex despite p110δ being the primary PI3K isoform found within monocytes. Concomitantly, SH2 domain-containing inositol 5-phosphatase 1 (SHIP1) was recruited to the gH/integrin β1 complex, which is critical to aberrant Akt activation, as SHIP1 diverts PI3K signaling toward a noncanonical pathway. Although integrin β1 was required for SHIP1 recruitment, gB-activated EGFR mediated SHIP1 activation, underscoring the importance of the interplay between gB- and gH-mediated signaling to the unique activation of Akt during HCMV infection. Indeed, SHIP1 activation mediated the increased expression of Mcl-1 and HSP27, two Akt-dependent antiapoptotic proteins specifically upregulated during HCMV infection but not during growth factor treatment. Overall, our data indicate that HCMV glycoproteins gB and gH work in concert to initiate an HCMV-specific signalosome responsible for the atypical activation of Akt required for infected monocyte survival and ultimately viral persistence. Human cytomegalovirus (HCMV) infection is endemic throughout the world regardless of socioeconomic conditions and geographic locations with a seroprevalence reaching up to 100% in some developing countries. Although asymptomatic in healthy individuals, HCMV can cause severe multiorgan disease in immunocompromised or immunonaive patients. HCMV disease is a direct consequence of monocyte-mediated systematic spread of the virus following infection. Because monocytes are short-lived cells, HCMV must subvert the natural short life-span of these blood cells by inducing a distinct activation of Akt, a serine/theonine protein kinase. In this work, we demonstrate that HCMV glycoproteins gB and gH work in tandem to reroute classical host cellular receptor signaling to aberrantly activate Akt and drive survival of infected monocytes. Deciphering how HCMV modulates the cellular pathway to induce monocyte survival is important to develop a new class of anti-HCMV drugs that could target and prevent spread of the virus by eliminating infected monocytes.
人类巨细胞病毒(HCMV)是免疫功能低下和免疫幼稚个体发病和死亡的主要原因。HCMV 诱导的病毒进入过程中的信号转导会迅速激活非典型 Akt,从而驱动寿命短暂的单核细胞分化为寿命较长的巨噬细胞,这对于病毒的传播和持续存在至关重要。我们发现 HCMV 糖蛋白 gB 和 gH 分别直接结合并激活细胞表皮生长因子受体(EGFR)和整合素β1,从而重塑单核细胞内经典的 Akt 信号转导。Akt 信号网络的重塑归因于非传统 Akt 激活物被招募到 gB 或 gH 产生的受体信号复合物中。尽管 p110δ 是单核细胞中主要的 PI3K 同工型,但包含 p110β 催化亚基的磷酯酰肌醇 3-激酶(PI3K)被招募到 gB/EGFR 复合物中。同时,SH2 结构域含有肌醇 5-磷酸酶 1(SHIP1)被招募到 gH/整合素β1 复合物中,这对于异常 Akt 激活至关重要,因为 SHIP1 将 PI3K 信号转向非典型途径。尽管整合素β1 是 SHIP1 募集所必需的,但 gB 激活的 EGFR 介导了 SHIP1 的激活,这强调了 gB-和 gH-介导的信号转导之间相互作用对于 HCMV 感染期间 Akt 的独特激活的重要性。事实上,SHIP1 的激活介导了 Mcl-1 和 HSP27 的表达增加,这两种 Akt 依赖性抗凋亡蛋白在 HCMV 感染期间特异性地上调,但在生长因子处理期间不上调。总的来说,我们的数据表明,HCMV 糖蛋白 gB 和 gH 协同作用,启动一个负责感染的单核细胞存活和最终病毒持续所需的 Akt 非典型激活的 HCMV 特异性信号体。无论社会经济条件和地理位置如何,人类巨细胞病毒(HCMV)感染在世界各地都很普遍,在一些发展中国家的血清流行率高达 100%。虽然在健康个体中无症状,但 HCMV 可导致免疫功能低下或免疫幼稚患者发生严重的多器官疾病。HCMV 疾病是病毒感染后单核细胞介导的系统性传播的直接后果。由于单核细胞是寿命短暂的细胞,因此 HCMV 必须通过诱导 Akt 的独特激活来颠覆这些血细胞的自然短暂寿命,Akt 是一种丝氨酸/苏氨酸蛋白激酶。在这项工作中,我们证明 HCMV 糖蛋白 gB 和 gH 协同作用,改变经典的宿主细胞受体信号转导,异常激活 Akt,并驱动感染单核细胞的存活。阐明 HCMV 如何调节细胞途径以诱导单核细胞存活对于开发新的一类抗 HCMV 药物很重要,这些药物可以通过消除感染的单核细胞来靶向和阻止病毒的传播。