Molecular characterization of suppression of hepatitis B virus transcription by hepatitis C virus core protein

Coiled-coil motif as a structural basis for the interaction of HTLV type 1 Tax with cellular cofactors

Human T lymphotropic virus type 1 (HTLV-1) Tax is a multifunctional protein centrally involved in transcriptional regulation, cell cycle control, and viral transformation. The regulatory functions of Tax are thought to be mediated through protein-protein interaction with cellular cofactors. Previously we have identified several novel binding partners for Tax, including human mitotic checkpoint protein MAD1 (TXBP181), G-protein pathway suppressor GPS2 (TXBP31), and IkappaB kinase regulatory subunit IKK-gamma. Here we described two additional Tax partners, TXBP151 and TXBP121. A closer examination of the sequences of eight independent cellular Tax-binding proteins identified by us and others revealed that all of them share a single characteristic, a highly structured coiled-coil domain. We also noted that Tax and the Tax-binding coiled-coil proteins can homodimerize. Additionally, the same domain in Tax is responsible for interaction with different coiled-coil proteins. Taken together, our findings point to a particular coiled-coil structure as one of the Tax-recognition motifs. The interaction of Tax with a particular subgroup of cellular coiled-coil proteins represents one mechanism by which Tax dysregulates cell growth and proliferation.

Isolation and complete nucleotide sequence of a Chinese Sindbis-like virus

Infection with alphaviruses is common in the Chinese population. Here we report the isolation of a Sindbis-like virus from a pool of Anopheles mosquitoes collected in Xinjiang, China during an arbovirus survey. This virus, designated XJ-160, rapidly produced cytopathic effects on mosquito and hamster cells. In addition, it was lethal to neonatal mice if inoculated intracerebrally. Serologically, XJ-160 reacted with and was neutralized by an anti-Sindbis antibody. Anti-XJ-160 antibodies were found in several cohorts of Chinese subjects. The complete 11626-base nucleotide sequence of XJ-160 was determined. XJ-160 has diverged significantly from the prototype Sindbis virus, with an 18% difference in nucleotide sequence and an 8.6% difference in amino acids; there are 11 deletions and 2 insertions, involving 99 nucleotides in total. XJ-160 is most closely linked to Kyzylagach virus isolated in Azerbaijan. Both belong to the African/European genetic lineage of Sindbis virus, albeit more distantly related to other members.

Hepatitis C virus core protein-induced loss of LZIP function correlates with cellular transformation

Hepatitis C virus (HCV) is the major etiological agent of blood-borne non-A non-B hepatitis and a leading cause of liver cirrhosis and hepatocellular carcinoma worldwide. HCV core protein is a multifunctional protein with regulatory functions in cellular transcription and virus-induced transformation and pathogenesis. Here we report on the identification of a bZIP nuclear transcription protein as an HCV core cofactor for transformation. This bZIP factor, designated LZIP, activates CRE-dependent transcription and regulates cell proliferation. Loss of LZIP function in NIH 3T3 cells triggers morphological transformation and anchorage-independent growth. We show that HCV core protein aberrantly sequesters LZIP in the cytoplasm, inactivates LZIP function and potentiates cellular transformation. Our findings suggest that LZIP might serve a novel cellular tumor suppressor function that is targeted by the HCV core.