Cyclin K Inhibits HIV-1 Gene Expression and Replication by Interfering with Cyclin-dependent Kinase 9 (CDK9)-Cyclin T1 Interaction in Nef-dependent Manner

Abstract

Human immunodeficiency virus type-1 (HIV-1) perpetuates its survival in the host by utilizing multiple strategies such as irreversible integration of its DNA into the host cell genome to establish the provirus (1), diversification of its genome to escape or tolerate adaptive immune responses (2), and use of the accessory genes (nef, vif, vpu, and vpr) to modulate host cell immune responses further (3-5). These viral accessory genes are frequently seen as dispensable in many in vitro cell culture systems but seem to be indispensable, in the context of natural infections in vivo. Among these accessory genes, pleiotropic functions of Nef have been studied extensively. It is a 27-30-kDa, N-terminally myristoylated protein having a well characterized CD4 down-regulatory activity (6). Nef does not possess any enzymatic activity, but it modulates diverse signaling pathways and the gene expression of host cell proteins (7,8). Furthermore, Nef influences the activation state of the host cell by bringing together different host cell proteins, protein kinases, and components of the endocytic machinery and making the cells permissible to the virus (9, 10). All these functions of Nef are manifested by a number of events such as activation of signaling molecules, modulation of apoptosis, activation of transcription factors, mitigation of transcriptional repressors, and an increase in the infectivity of virions (11). Although these functions of Nef have been well studied, controversy exists on its role in viral infectivity and replication as both negative (12, 13) and positive (14, 15) roles have been attributed in the literature. Although a number of reports show that Nef increases viral replication by activating T-cells, the molecular basis of Nef-induced viral gene expression and replication remains to be clearly elucidated. Nef was also shown to physically interact with Tat and augment viral gene expression (16), although availability of Tat is critical for the elongation step of long terminal repeat (LTR) 2 -driven transcription by RNA polymerase II. Several cellular factors have been identified for their roles in this process, including positive transcription elongation factor b (P-TEFb) complex. Different P-TEFb complexes isolated from mammalian cells contain a common catalytic subunit, cyclin-dependent kinase 9 (CDK9), and one of the regulatory cyclins, CycT1, CycT2a, CycT2b,. However, CycT1-containing P-TEFb complex is the key complex responsible for HIV-1 transcription elongation (19). Tat is expressed early in the replicative cycle of HIV and is essential for viral gene expression from the LTR promoter. It recognizes the 5Ј-bulge in the transactivation response stem loop RNA, which is located at the 5Ј-end of all viral transcripts. Tat binds to CycT1, and together they form the combinatorial surface that interacts with the transactivation response RNA with high affinity and specificity. The obligate partner of CycT1, CDK9, then hyperphosphorylates the C-terminal domain (CTD) of RNA polymerase II, resulting in incre...

Crosstalk in competing endogenous RNA networks reveals new circular RNAs involved in the pathogenesis of early HIV infection

“…miR-27b has been reported to regulate HIV-1 replication and the expression of cyclin T1 in resting CD4 T cells, cyclin T1 is a regulatory subunit of a positive RNA polymerase II transcription elongation factor also known as P-TEFb and is also needed for Tat transactivation of HIV-1 gene expression [ 63 ]. CCNK, also named Cyclin K, was found to displace cyclin T1 from the P-TEFb complex by utilizing HIV-1 Nef protein, resulting in the inhibition of HIV-1 gene expression and replication [ 64 ]. This study revealed 18 circRNAs may function as miRNA sponges of miR-27b to regulate HIV-1 replication via regulating the expression of CCNK.…”

Kinases: Understanding Their Role in HIV Infection

“…Using yeast two-hybrid, immunoprecipitation and colocalization Khan et al identified interaction of CCNK with HIV Nef. Implication of CCCK inhibitory role in HIV infection was shower in overexpression of CCNK and siRNA knockout of CCNK in Jurkat cells where reduced HIV production and enhance viral released respectively [37].…”

Interaction of Cyclin-Dependent Kinase 12/CrkRS with Cyclin K1 Is Required for the Phosphorylation of the C-Terminal Domain of RNA Polymerase II

“…For example, interaction of CDK9 p42 /cyclin T1 with the viral Tat protein facilitates the transactivation of the long terminal repeat of human immunodeficiency virus type 1 (HIV-1) and HIV-2 and is essential for productive viral replication (22). Recently, cyclin K was found to inhibit HIV-1 gene expression and replication through its interaction with HIV-1 Nef (32). CDK9/cyclin T2 complexes interact with PKN␣ and Rho-activated Ser/Thr kinase and are involved in regulating terminal differentiation in muscle cells through activation of Myo-D (12,58).…”