Dr. Ricciardi's laboratory (click here to see us) studies the mechanisms by which viral proteins of human DNA viruses regulate gene expression and produce disease and cancer. Current areas of research are:
I. The mechanism of E1A mediated tumorigenesis.
Ad12 transformed cells
are able to cause tumors in immune competent rodents. In Ad12 transformed
cells, the surface levels of the major histocompatibility class I antigens
become greatly diminished,
enabling them to escape immunosurveillance by cytotoxic T lymphocytes.
The E1A-12 protein mediates this effect by altering the binding of two
transcription factors
to the class I enhancer which, in turn, blocks transcription from the class
I promoter. Specifically, the activator NF-kB becomes hypophosphorylated
which
disables it from binding
to its cognate recognition site on the class I enhancer. In addition,
the repressor COUP-TF becomes strongly bound to a different recognition
site on the class I enhancer, causing histone deacetylation and chromatin
compaction. In this way, E1A-12 mediates total transcriptional shut-off
of the class I promoter. Exactly how E1A-12 mediates these effects
needs to be understood. In addition to class I shut-off, E1A-12 contains
a novel domain which appears to encode a new function that is also
necessary for tumorigenesis.
A cellular protein which binds to this novel domain has just been isolated
and its role in tumorigenesis needs to be explored.
II. Structure and
function of the E1A-5 transactivating protein:
Critical to understanding
gene expression is the manner by which transcriptional promoters are stimulated
by transactivating proteins. The E1A-5 protein of adenovirus
contains a 46 amino acid
transactivating domain that stimulates promoters by functioning as a bridge
between the basal transcription complex and upstream factor
binding sites. A
zinc finger within the transactivating domain binds to the TATA box binding
protein (TBP) and a newly discovered cellular factor, hSur-2 (a subunit
of human
mediator complex), while
residues flanking the zinc finger associate with other basal transcription
factors, referred to as TAFs. The way in which E1A-5 and
the cellular proteins
interact are being investigated using genetic, biochemical and structural
approaches.
approaches.
III. The processivity
Factor of HHV-8: Mechanism and antiviral targeting.
HHV-8 (KSHV) is a newly
discovered human herpesviruses which is the etiological agent of Kaposi’s
sarcoma (KS) and certain B-cell lymphomas. The processivity factor of HHV-8
(PF-8) enables the viral DNA polymerase (Pol-8) to remain on the template
and is critical for DNA synthesis. For example, Pol-8 alone incorporates
only three dNTPs whereas a 7,249 deoxynucleotide full-length test-template
is synthesized when PF-8 is present. Moreover, this KSHV complex
is specific in that other processivity factors and polymerases cannot substitute
for PF-8 or Pol-8. We are exploring the manner by which PF-8 tethers
Pol-8 to the template and yet enables the complex to move along the DNA.
A mechanistic screen has been designed for high-throughput robotic-testing
of hundreds-of-thousands of compounds for their abilities to block DNA
synthesis by Pol-8 and PF-8. Compounds that block DNA synthesis in vitro,
will be tested for their abilities to block KSHV infection.
