REGULATION OF EXPRESSION OF CLASS II MAJOR HISTOCOMPATIBILITY COMPLEX 
AND HUMAN IMMUNODEFICIENCY VIRUS GENES 
B. Matija Peterlin, M.D., Assistant Investigator 
Dr. Peterlin and his colleagues are studying the 
regulation of expression of genes that affect the im- 
mune system, namely those that code for class II 
major histocompatibility complex (MHC; class II, 
DR) antigens and human immunodeficiency virus 
(HIV) proteins. Different levels of expression of 
these proteins in humans lead to severe combined 
immunodeficiency and predispose to autoimmu- 
nity. Class II and HIV are further linked by genetics, 
since low expression of each can be complemented 
in trans, i.e., by rescuing the gene(s) missing or 
mutated in the class II bare lymphocyte syndrome 
(BLS II; the only hereditary deficiency in a regula- 
tory protein in humans) and by HIV-encoded trans- 
activators TAT and REV 
I. Regulation of Class II Gene Expression. 
Class II antigens are peptide carriers that present 
self and foreign peptides to T cells to initiate and 
help T helper cells to interact v^^ith B cells to propa- 
gate the immune response. Developmentally class 
II antigens must be expressed in the thymus to 
tolerize T cells to self proteins and to restrict T cells 
to nonself peptides. For these interactions to occur, 
the expression of class II genes must be carefully 
regulated. 
A. Cis-acting sequences. Dr. Peterlin has extensively 
characterized transcriptional enhancer and pro- 
moter elements in the DRA gene. DRA promoter is 
bipartite, consisting of upstream promoter ele- 
ments that are activated by interferon-7 and can 
confer B cell specificity and downstream promoter 
elements that position RNA polymerase II and lead 
to proper initiation of transcription. It is in these 
upstream promoter elements that DOB, DQA2, and 
DQB2 genes have mutations that result in aberrant 
expression (DOB) or nonexpression (DQA2, DQB2) 
of these genes. Furthermore, by using cluster point 
mutations in the DRA promoter. Dr. Peterlin found 
that identical cis-acting sequences are required for 
interferon-7 inducibility and B cell specificity. 
B. Trans-acting factors. Dr. Peterlin has character- 
ized proteins that interact with DRA transcriptional 
enhancer and promoter elements. In the transcrip- 
tional enhancer, OCT-1 and OCT-2 bind to the octa- 
mer box and C/EBP (core/enhancer binding pro- 
tein) to the core enhancer element. In the pro- 
moter, OCT-1 and OCT-2 bind to the octamer, NF-Y 
to the Y box, NF-Xc and X2 to the X box, and NF-Zc 
and Z2 to the Z box. The Z box is a duplication of 
the X box, since in competition experiments, X box 
oligonucleotides compete off Z box-binding pro- 
teins. Proteins that interact with X and Z boxes are 
not fundamentally different in cells representing 
distinct class II phenotypes. Thus tissue specificity 
might be due to proteins that interact with these 
DNA-binding proteins. Dr. Goran Andersson in Dr. 
Peterlin's laboratory has now isolated four cDNA 
clones that code for proteins that bind to X and Z 
boxes. They have been extensively characterized; 
two code for NF-Xc and one for NF-X2. 
C. BLS II and class Il-negative B cell lines. Dr. An- 
drew Caiman in Dr. Peterlin's laboratory developed 
class Il-negative mutant B cell lines RM2 and RM3. 
Recently, other class Il-negative B cell lines and 
BLS II cells were obtained. By transient fusions of 
these cells, three complementation groups leading 
to nonexpression of class II in B cells are found. 
None of these cells have gross defects in NF-Xc and 
NF-Zc. Although Dr. Peterlin has attempted to res- 
cue these cells by gene complementation, using ex- 
pression cDNA Ubraries, he has not yet rescued the 
defect in RM3. Genetic approaches and cDNA 
clones isolated by Dr. Andersson are being used to 
complement class Il-negative and BLS II cells. 
II. Regulation of HIV Gene Expression. 
HIV causes acquired immune deficiency syn- 
drome (AIDS) and requires the expression of the 
TAT and REV proteins for efficient viral replication 
and gene expression. Dr. Peterlin studies the mech- 
anism of action of TAT on its trans-active-responsive 
region (TAR). 
A. Trans-activation by TAT. The 1 5 kDa protein TAT 
is encoded by doubly spliced HIV RNA; TAT appears 
early in the viral life cycle and acts on 5' HIV RNA 
sequences. Interactions between TAT and TAR lead 
to increased levels of HIV RNA and even higher lev- 
els of HIV proteins. Dr. Peterlin determined that 
TAT does not increase the rates of initiation of HIV 
transcription but facilitates expression of full- 
length HIV RNA. In the absence of TAT, short tran- 
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