LANA

The latency-associated nuclear antigen (LANA-1) or latent nuclear antigen (LNA, LNA-1) is a Kaposi's sarcoma-associated herpesvirus (KSHV) latent protein initially found by Moore and colleagues as a speckled nuclear antigen present in primary effusion lymphoma cells that reacts with antibodies from patients with KS. It is the most immunodominant KSHV protein identified by Western-blotting as 222–234 kDa double bands migrate slower than the predicted molecular weight. LANA has been suspected of playing a crucial role in modulating viral and cellular gene expression. It is commonly used as an antigen in blood tests to detect antibodies in persons that have been exposed to KSHV.

KSHV or Human herpesvirus 8 (HHV-8) has been identified as the etiological agent of Kaposi’s sarcoma (KS) and certain AIDS-associated lymphomas. As KSHV establishes latent infection in tumorous foci, it invariably expresses high levels of the viral LANA protein, which is necessary and sufficient to maintain the KSHV episome.

Encoded by ORF73, LANA-1 is one of few HHV-8 encoded proteins that is highly expressed in all latently infected tumour cells; specifically, it is a phosphoprotein with an acidic internal repeat domain flanked by a carboxy-terminal domain and an amino-terminal domain. LANA-1 acts as a transcriptional regulator, and it has been implicated directly in oncogenesis because of its ability to bind to the tumour-suppressing protein p53 and to the retinoblastoma protein pRb. This leads to the inactivation of p53-dependent promoters and induction of E2F-dependent genes.

Studies have also shown that LANA-1 can transactivate the promoter of the reverse transcriptase subunit of the human telomerase holoenzyme, thus overextending a critical step in cellular transformation. Paradoxically, LANA-1 has been shown to be involved in transcriptional repression and can, moreover, interact with the mSin3/HDAC1 co-repressor complex.

It has been also shown to interact with and inhibit the ATF4/CREB2 transcription factor that interacts with the basic transcription machinery and to bind with two human chromosome-associated cellular proteins, MeCP2 and DEK.

LANA-1 is associated with cellular chromatin and stays on the chromosomes during cell division. It maintains the viral genomes during cell division by tethering the viral episomes to the chromosomes. It binds directly to replication origin recognition complexes (ORCs) that are primarily associated with the terminal repeat (TR) region of the HHV-8 genome.

References

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2. (July 1996). "Seroconversion to antibodies against Kaposi's sarcoma-associated herpesvirus-related latent nuclear antigens before the development of Kaposi's sarcoma". The New England Journal of Medicine.
3. (November 1997). "Identification of the gene encoding the major latency-associated nuclear antigen of the Kaposi's sarcoma-associated herpesvirus". The Journal of Clinical Investigation.
4. (1997). "Identification of a major latent nuclear antigen, LNA-1, in the human herpesvirus 8 genome". Journal of Human Virology.
5. (August 1997). "The 222- to 234-kilodalton latent nuclear protein (LNA) of Kaposi's sarcoma-associated herpesvirus (human herpesvirus 8) is encoded by orf73 and is a component of the latency-associated nuclear antigen". Journal of Virology.
6. (August 1996). "KSHV antibodies among Americans, Italians and Ugandans with and without Kaposi's sarcoma". Nature Medicine.
7. (August 1996). "The seroepidemiology of human herpesvirus 8 (Kaposi's sarcoma-associated herpesvirus): distribution of infection in KS risk groups and evidence for sexual transmission". Nature Medicine.
8. (1999). "p53 inhibition by the LANA protein of KSHV protects against cell death". Nature.
9. (March 2002). "The KSHV latency-associated nuclear antigen: a multifunctional protein". Frontiers in Bioscience.
10. (April 2004). "Regulation and autoregulation of the promoter for the latency-associated nuclear antigen of Kaposi's sarcoma-associated herpesvirus". The Journal of Biological Chemistry.
11. (July 2002). "Latency-associated nuclear antigen (LANA) cooperatively binds to two sites within the terminal repeat, and both sites contribute to the ability of LANA to suppress transcription and to facilitate DNA replication". The Journal of Biological Chemistry.
12. (October 2000). "Human herpesvirus 8 LANA interacts with proteins of the mSin3 corepressor complex and negatively regulates Epstein-Barr virus gene expression in dually infected PEL cells". Journal of Virology.
13. (September 2000). "Carboxy terminus of human herpesvirus 8 latency-associated nuclear antigen mediates dimerization, transcriptional repression, and targeting to nuclear bodies". Journal of Virology.
14. (November 2000). "Latency-associated nuclear antigen of Kaposi's sarcoma-associated herpesvirus (human herpesvirus-8) binds ATF4/CREB2 and inhibits its transcriptional activation activity". The Journal of General Virology.
15. (June 1998). "Restricted expression of Epstein-Barr virus (EBV)-encoded, growth transformation-associated antigens in an EBV- and human herpesvirus type 8-carrying body cavity lymphoma line". The Journal of General Virology.
16. (April 1999). "Efficient persistence of extrachromosomal KSHV DNA mediated by latency-associated nuclear antigen". Science.
17. (April 2006). "Kaposi's sarcoma-associated herpesvirus-encoded latency-associated nuclear antigen modulates K1 expression through its cis-acting elements within the terminal repeats". Journal of Virology.